[PATCH 00/10] net: support thread-specific pidfds for send and connect

[PATCH 00/10] net: support thread-specific pidfds for send and connect

[Christian Brauner]

SO_PASSPIDFD/SCM_PIDFD and SO_PEERPIDFD allow to retrieve a pidfd for
the thread-group leader. The coredump server using the coredump socket
cannot get a handle on the task that took the signal and is writing the
coredump easily. Workloads interested in per-thread authentification
have similar problems.

Add SO_PASSPIDFD_THREAD and SO_PEERPIDFD_THREAD. We record the sending
and the connecting thread in addition to the thread-group leader.

SO_PASSPIDFD_THREAD functions like SO_PASSPIDFD but instead of an
SCM_PIDFD message for the thread-group leader, SCM_PIDFD sends a pidfd
for the specific thread. SO_PASSPIDFD_THREAD is mutually exclusive with
SO_PASSPIDFD. The last one set takes precedence and disables the other
one. Both SO_PASSCRED and SO_PASSPIDFD receivers see one writer per
process as before.

SO_PEERPIDFD_THREAD allows to retrieve a pidfd for the specific thread
that called connect(), listen(), or socketpair().

pidfs_coredump() now also stamps the dumping thread's struct pid so a
pidfd for that thread reports the coredump like the pidfd of the
thread-group leader does.

Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
---
Christian Brauner (10):
      pid: add helpers to operate on a struct pid array
      af_unix: record the pid of the sending thread
      net: add SO_PASSPIDFD_THREAD to get a thread-specific SCM_PIDFD
      selftests/net: SO_PASSPIDFD_THREAD
      net: turn sk_peer_pid into an array indexed by pid type
      af_unix: record the pid of the connecting thread
      net: add SO_PEERPIDFD_THREAD to get a thread-specific pidfd
      selftests/net: SO_PEERPIDFD_THREAD
      pidfs: record the coredump on the dumping thread's pid too
      selftests/coredump: check the dumping thread's pidfd

 arch/alpha/include/uapi/asm/socket.h               |   4 +
 arch/mips/include/uapi/asm/socket.h                |   4 +
 arch/parisc/include/uapi/asm/socket.h              |   4 +
 arch/sparc/include/uapi/asm/socket.h               |   4 +
 fs/coredump.c                                      |  22 +-
 fs/pidfs.c                                         |  27 +-
 include/linux/coredump.h                           |   4 +-
 include/linux/pid.h                                |  53 +++
 include/linux/pid_types.h                          |   8 +
 include/linux/pidfs.h                              |   5 +
 include/linux/sched/signal.h                       |  18 +
 include/net/scm.h                                  |   7 +-
 include/net/sock.h                                 |  14 +-
 include/uapi/asm-generic/socket.h                  |   4 +
 net/bluetooth/af_bluetooth.c                       |   6 +-
 net/bluetooth/hci_sock.c                           |   8 +-
 net/bluetooth/l2cap_sock.c                         |   2 +-
 net/core/scm.c                                     |  36 +-
 net/core/sock.c                                    | 120 ++++---
 net/unix/af_unix.c                                 |  67 ++--
 net/unix/af_unix.h                                 |   3 +-
 .../selftests/coredump/coredump_socket_test.c      | 175 ++++++++++
 tools/testing/selftests/coredump/coredump_test.h   |   2 +
 .../selftests/coredump/coredump_test_helpers.c     |  49 +++
 tools/testing/selftests/net/af_unix/Makefile       |   2 +
 tools/testing/selftests/net/af_unix/scm_pidfd.c    | 366 +++++++++++++++++++++
 26 files changed, 905 insertions(+), 109 deletions(-)
---
base-commit: cee9395acd8043be0644b25c34bfa86623f2b935
change-id: 20260825-work-unix-passpidfd-086a1ec09e8a

[PATCH 01/10] pid: add helpers to operate on a struct pid array

[Christian Brauner]

We're about to extend af_unix sockets and coredump code with the ability
to hand out thread-specific pidfds. Add a few simple helpers that allow
to operate on multiple struct pids up to PIDTYPE_MAX with automatic
bounds checking.

Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
---
 fs/pidfs.c                   | 16 +++++++++++++
 include/linux/pid.h          | 53 ++++++++++++++++++++++++++++++++++++++++++++
 include/linux/pid_types.h    |  8 +++++++
 include/linux/pidfs.h        |  5 +++++
 include/linux/sched/signal.h | 18 +++++++++++++++
 5 files changed, 100 insertions(+)

diff --git a/fs/pidfs.c b/fs/pidfs.c
index a6a643f15d08..586af2e5811c 100644
--- a/fs/pidfs.c
+++ b/fs/pidfs.c
@@ -1070,6 +1070,22 @@ int pidfs_register_pid_gfp(struct pid *pid, gfp_t gfp)
 	return 0;
 }
 
+/* Register the pids up to pid type @last of @pids in pidfs. */
+int __pidfs_register_pids(struct pid *const *pids, enum pid_type last)
+{
+	if (WARN_ON_ONCE(last >= PIDTYPE_MAX))
+		return -EINVAL;
+
+	for (enum pid_type type = PIDTYPE_PID; type <= last; type++) {
+		int ret = pidfs_register_pid(pids[type]);
+
+		if (unlikely(ret))
+			return ret;
+	}
+
+	return 0;
+}
+
 static struct dentry *pidfs_stash_dentry(struct dentry **stashed,
 					 struct dentry *dentry)
 {
diff --git a/include/linux/pid.h b/include/linux/pid.h
index ddaef0bbc8ba..87635d0cc1f7 100644
--- a/include/linux/pid.h
+++ b/include/linux/pid.h
@@ -2,6 +2,9 @@
 #ifndef _LINUX_PID_H
 #define _LINUX_PID_H
 
+#include <linux/array_size.h>
+#include <linux/build_bug.h>
+#include <linux/minmax.h>
 #include <linux/pid_types.h>
 #include <linux/rculist.h>
 #include <linux/rcupdate.h>
@@ -92,6 +95,56 @@ static inline struct pid *get_pid(struct pid *pid)
 }
 
 extern void put_pid(struct pid *pid);
+
+/*
+ * Helpers for arrays of struct pid indexed by pid type declared with
+ * DECLARE_PIDS(). The array covers PIDTYPE_PID up to the pid type it
+ * was declared with and the helpers take that bound from the array.
+ */
+static inline void __get_pids(struct pid **dst, struct pid *const *src,
+			      enum pid_type last)
+{
+	for (enum pid_type type = PIDTYPE_PID; type <= last; type++)
+		dst[type] = get_pid(src[type]);
+}
+
+static inline void __put_pids(struct pid **pids, enum pid_type last)
+{
+	for (enum pid_type type = PIDTYPE_PID; type <= last; type++) {
+		put_pid(pids[type]);
+		pids[type] = NULL;
+	}
+}
+
+static inline void __swap_pids(struct pid **a, struct pid **b,
+			       enum pid_type last)
+{
+	for (enum pid_type type = PIDTYPE_PID; type <= last; type++)
+		swap(a[type], b[type]);
+}
+
+static inline bool __pids_equal(struct pid *const *a, struct pid *const *b,
+				enum pid_type last)
+{
+	for (enum pid_type type = PIDTYPE_PID; type <= last; type++)
+		if (a[type] != b[type])
+			return false;
+	return true;
+}
+
+/* The last pid type an array declared with DECLARE_PIDS() covers. */
+#define pids_last(pids)							\
+	((enum pid_type)(ARRAY_SIZE(pids) - 1 +				\
+			 BUILD_BUG_ON_ZERO(ARRAY_SIZE(pids) > PIDTYPE_MAX)))
+
+#define __pids_last2(a, b)						\
+	(pids_last(a) + BUILD_BUG_ON_ZERO(ARRAY_SIZE(a) != ARRAY_SIZE(b)))
+
+#define get_pids(dst, src)	__get_pids(dst, src, __pids_last2(dst, src))
+#define put_pids(pids)		__put_pids(pids, pids_last(pids))
+#define swap_pids(a, b)		__swap_pids(a, b, __pids_last2(a, b))
+#define pids_equal(a, b)	__pids_equal(a, b, __pids_last2(a, b))
+
 extern struct task_struct *pid_task(struct pid *pid, enum pid_type);
 static inline bool pid_has_task(struct pid *pid, enum pid_type type)
 {
diff --git a/include/linux/pid_types.h b/include/linux/pid_types.h
index c2aee1d91dcf..3302690a2a28 100644
--- a/include/linux/pid_types.h
+++ b/include/linux/pid_types.h
@@ -2,6 +2,8 @@
 #ifndef _LINUX_PID_TYPES_H
 #define _LINUX_PID_TYPES_H
 
+#include <linux/build_bug.h>
+
 enum pid_type {
 	PIDTYPE_PID,
 	PIDTYPE_TGID,
@@ -10,6 +12,12 @@ enum pid_type {
 	PIDTYPE_MAX,
 };
 
+struct pid;
+
+/* An array of struct pid indexed by pid type, PIDTYPE_PID up to @last. */
+#define DECLARE_PIDS(name, last)					\
+	struct pid *name[(last) + 1 + BUILD_BUG_ON_ZERO((last) >= PIDTYPE_MAX)]
+
 struct pid_namespace;
 extern struct pid_namespace init_pid_ns;
 
diff --git a/include/linux/pidfs.h b/include/linux/pidfs.h
index 0abf7da9ab23..3c1e82f1a369 100644
--- a/include/linux/pidfs.h
+++ b/include/linux/pidfs.h
@@ -3,6 +3,7 @@
 #define _LINUX_PID_FS_H
 
 #include <linux/gfp_types.h>
+#include <linux/pid.h>
 
 struct coredump_params;
 
@@ -32,5 +33,9 @@ static inline int pidfs_register_pid(struct pid *pid)
 }
 
 void pidfs_free_pid(struct pid *pid);
+int __pidfs_register_pids(struct pid *const *pids, enum pid_type last);
+
+/* Register the pids of an array declared with DECLARE_PIDS(). */
+#define pidfs_register_pids(pids)	__pidfs_register_pids(pids, pids_last(pids))
 
 #endif /* _LINUX_PID_FS_H */
diff --git a/include/linux/sched/signal.h b/include/linux/sched/signal.h
index 584ae88b435e..9444b47789a0 100644
--- a/include/linux/sched/signal.h
+++ b/include/linux/sched/signal.h
@@ -677,6 +677,24 @@ struct pid *task_pid_type(struct task_struct *task, enum pid_type type)
 	return pid;
 }
 
+/* Fill @pids with the pid types of @task up to @last, without references. */
+static inline void __task_pids(struct pid **pids, enum pid_type last,
+			       struct task_struct *task)
+{
+	for (enum pid_type type = PIDTYPE_PID; type <= last; type++)
+		pids[type] = task_pid_type(task, type);
+}
+
+static inline void __get_task_pids(struct pid **pids, enum pid_type last,
+				   struct task_struct *task)
+{
+	for (enum pid_type type = PIDTYPE_PID; type <= last; type++)
+		pids[type] = get_pid(task_pid_type(task, type));
+}
+
+#define task_pids(pids, task)		__task_pids(pids, pids_last(pids), task)
+#define get_task_pids(pids, task)	__get_task_pids(pids, pids_last(pids), task)
+
 static inline struct pid *task_tgid(struct task_struct *task)
 {
 	return task->signal->pids[PIDTYPE_TGID];

-- 
2.53.0

[PATCH 02/10] af_unix: record the pid of the sending thread

[Christian Brauner]

Currently only the struct pid of the thread-group leader is recorded.
The identity of the actual thread that sent the message or is connected
to a given socket cannot be retrieved.

Add the plumbing to make it possible to retrieve a pidfd for the sender.
Nothing uses the thread-specific struct pid yet. No functional changes.

Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
---
 include/net/scm.h  |  7 +++----
 net/core/scm.c     | 21 +++++++++++++++++----
 net/unix/af_unix.c | 23 +++++++++++++----------
 net/unix/af_unix.h |  3 ++-
 4 files changed, 35 insertions(+), 19 deletions(-)

diff --git a/include/net/scm.h b/include/net/scm.h
index 86ae6bc109ec..aa7d15c5fc27 100644
--- a/include/net/scm.h
+++ b/include/net/scm.h
@@ -42,7 +42,7 @@ struct scm_fp_list {
 };
 
 struct scm_cookie {
-	struct pid		*pid;		/* Skb credentials */
+	DECLARE_PIDS(pid, PIDTYPE_TGID);	/* Skb credentials by pid type */
 	struct scm_fp_list	*fp;		/* Passed files		*/
 	struct scm_creds	creds;		/* Skb credentials	*/
 #ifdef CONFIG_SECURITY_NETWORK
@@ -69,7 +69,7 @@ static __inline__ void unix_get_peersec_dgram(struct socket *sock, struct scm_co
 static __inline__ void scm_set_cred(struct scm_cookie *scm,
 				    struct pid *pid, kuid_t uid, kgid_t gid)
 {
-	scm->pid = get_pid(pid);
+	scm->pid[PIDTYPE_TGID] = get_pid(pid);
 	scm->creds.pid = pid_vnr(pid);
 	scm->creds.uid = uid;
 	scm->creds.gid = gid;
@@ -77,8 +77,7 @@ static __inline__ void scm_set_cred(struct scm_cookie *scm,
 
 static __inline__ void scm_destroy_cred(struct scm_cookie *scm)
 {
-	put_pid(scm->pid);
-	scm->pid = NULL;
+	put_pids(scm->pid);
 }
 
 static __inline__ void scm_destroy(struct scm_cookie *scm)
diff --git a/net/core/scm.c b/net/core/scm.c
index f0d44ecdb11f..9b9e119c353a 100644
--- a/net/core/scm.c
+++ b/net/core/scm.c
@@ -149,6 +149,7 @@ EXPORT_SYMBOL(__scm_destroy);
 
 static inline int scm_replace_pid(struct scm_cookie *scm, struct pid *pid)
 {
+	struct pid *thread_pid;
 	int err;
 
 	/* drop all previous references */
@@ -158,7 +159,18 @@ static inline int scm_replace_pid(struct scm_cookie *scm, struct pid *pid)
 	if (unlikely(err))
 		return err;
 
-	scm->pid = pid;
+	/* A sender naming its own thread-group sends from the current thread. */
+	if (pid == task_tgid(current))
+		thread_pid = task_pid(current);
+	else
+		thread_pid = pid;
+
+	err = pidfs_register_pid(thread_pid);
+	if (unlikely(err))
+		return err;
+
+	scm->pid[PIDTYPE_TGID] = pid;
+	scm->pid[PIDTYPE_PID] = get_pid(thread_pid);
 	scm->creds.pid = pid_vnr(pid);
 	return 0;
 }
@@ -207,7 +219,8 @@ int __scm_send(struct socket *sock, struct msghdr *msg, struct scm_cookie *p)
 			if (err)
 				goto error;
 
-			if (!p->pid || pid_vnr(p->pid) != creds.pid) {
+			if (!p->pid[PIDTYPE_TGID] ||
+			    pid_vnr(p->pid[PIDTYPE_TGID]) != creds.pid) {
 				struct pid *pid;
 				err = -ESRCH;
 				pid = find_get_pid(creds.pid);
@@ -504,10 +517,10 @@ static void scm_pidfd_recv(struct msghdr *msg, struct scm_cookie *scm)
 		return;
 	}
 
-	if (!scm->pid)
+	if (!scm->pid[PIDTYPE_TGID])
 		return;
 
-	pidfd = pidfd_prepare(scm->pid, PIDFD_STALE, &pidfd_file);
+	pidfd = pidfd_prepare(scm->pid[PIDTYPE_TGID], PIDFD_STALE, &pidfd_file);
 
 	if (put_cmsg(msg, SOL_SOCKET, SCM_PIDFD, sizeof(int), &pidfd)) {
 		if (pidfd_file) {
diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 13f9926bf205..011af84e3626 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -1973,7 +1973,7 @@ static void unix_destruct_scm(struct sk_buff *skb)
 {
 	struct scm_cookie scm = {};
 
-	swap(scm.pid, UNIXCB(skb).pid);
+	swap_pids(scm.pid, UNIXCB(skb).pid);
 
 	if (UNIXCB(skb).fp)
 		unix_detach_fds(&scm, skb);
@@ -1991,7 +1991,7 @@ static int unix_scm_to_skb(struct scm_cookie *scm, struct sk_buff *skb, bool sen
 {
 	int err = 0;
 
-	UNIXCB(skb).pid = get_pid(scm->pid);
+	get_pids(UNIXCB(skb).pid, scm->pid);
 	UNIXCB(skb).uid = scm->creds.uid;
 	UNIXCB(skb).gid = scm->creds.gid;
 	UNIXCB(skb).fp = NULL;
@@ -2005,7 +2005,10 @@ static int unix_scm_to_skb(struct scm_cookie *scm, struct sk_buff *skb, bool sen
 
 static void unix_skb_to_scm(struct sk_buff *skb, struct scm_cookie *scm)
 {
-	scm_set_cred(scm, UNIXCB(skb).pid, UNIXCB(skb).uid, UNIXCB(skb).gid);
+	get_pids(scm->pid, UNIXCB(skb).pid);
+	scm->creds.pid = pid_vnr(scm->pid[PIDTYPE_TGID]);
+	scm->creds.uid = UNIXCB(skb).uid;
+	scm->creds.gid = UNIXCB(skb).gid;
 	unix_set_secdata(scm, skb);
 }
 
@@ -2025,20 +2028,20 @@ static void unix_skb_to_scm(struct sk_buff *skb, struct scm_cookie *scm)
 static int unix_maybe_add_creds(struct sk_buff *skb, const struct sock *sk,
 				const struct sock *other)
 {
-	if (UNIXCB(skb).pid)
+	if (UNIXCB(skb).pid[PIDTYPE_TGID])
 		return 0;
 
 	if (unix_may_passcred(sk) || unix_may_passcred(other) ||
 	    !other->sk_socket) {
-		struct pid *pid;
 		int err;
 
-		pid = task_tgid(current);
-		err = pidfs_register_pid(pid);
-		if (unlikely(err))
+		get_task_pids(UNIXCB(skb).pid, current);
+		err = pidfs_register_pids(UNIXCB(skb).pid);
+		if (unlikely(err)) {
+			put_pids(UNIXCB(skb).pid);
 			return err;
+		}
 
-		UNIXCB(skb).pid = get_pid(pid);
 		current_uid_gid(&UNIXCB(skb).uid, &UNIXCB(skb).gid);
 	}
 
@@ -2048,7 +2051,7 @@ static int unix_maybe_add_creds(struct sk_buff *skb, const struct sock *sk,
 static bool unix_skb_scm_eq(struct sk_buff *skb,
 			    struct scm_cookie *scm)
 {
-	return UNIXCB(skb).pid == scm->pid &&
+	return UNIXCB(skb).pid[PIDTYPE_TGID] == scm->pid[PIDTYPE_TGID] &&
 	       uid_eq(UNIXCB(skb).uid, scm->creds.uid) &&
 	       gid_eq(UNIXCB(skb).gid, scm->creds.gid) &&
 	       unix_secdata_eq(scm, skb);
diff --git a/net/unix/af_unix.h b/net/unix/af_unix.h
index 8119dbeef3a3..402742895acc 100644
--- a/net/unix/af_unix.h
+++ b/net/unix/af_unix.h
@@ -2,6 +2,7 @@
 #ifndef __AF_UNIX_H
 #define __AF_UNIX_H
 
+#include <linux/pid_types.h>
 #include <linux/uidgid.h>
 
 #define UNIX_HASH_MOD	(256 - 1)
@@ -11,7 +12,7 @@
 struct sock *unix_peer_get(struct sock *sk);
 
 struct unix_skb_parms {
-	struct pid		*pid;		/* skb credentials	*/
+	DECLARE_PIDS(pid, PIDTYPE_TGID);	/* skb credentials by pid type */
 	kuid_t			uid;
 	kgid_t			gid;
 	struct scm_fp_list	*fp;		/* Passed files		*/

-- 
2.53.0

[PATCH 03/10] net: add SO_PASSPIDFD_THREAD to get a thread-specific SCM_PIDFD

[Christian Brauner]

Currently, SCM_PIDFD carries a pidfd for the thread-group leader. A
broker or the coredump server cannot learn the identity of the specific
thread that sent a given message. Now that both struct pids are recorded
a receiver can ask for the specific identity it needs.

So add SO_PASSPIDFD_THREAD as a sibling of SO_PASSPIDFD. Either option
makes recvmsg() deliver an SCM_PIDFD. SO_PASSPIDFD sends a pidfd for the
thread-group leader and SO_PASSPIDFD_THREAD sends a pidfd for the
specific thread.

The two options are mutually exclusive. Enabling one switches the other
off, so getsockopt() always reports which of the two is active.

On SOCK_STREAM sockets recvmsg() only stops merging data at a thread
boundary when the receiver asked for a thread pidfd. For SO_PASSCRED and
SO_PASSPIDFD receivers all threads of one process remain a single
writer.

Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
---
 arch/alpha/include/uapi/asm/socket.h  |  2 ++
 arch/mips/include/uapi/asm/socket.h   |  2 ++
 arch/parisc/include/uapi/asm/socket.h |  2 ++
 arch/sparc/include/uapi/asm/socket.h  |  2 ++
 include/net/sock.h                    | 10 +++++++++-
 include/uapi/asm-generic/socket.h     |  2 ++
 net/core/scm.c                        | 19 +++++++++++++------
 net/core/sock.c                       | 26 ++++++++++++++++++++++++--
 net/unix/af_unix.c                    | 11 ++++++++---
 9 files changed, 64 insertions(+), 12 deletions(-)

diff --git a/arch/alpha/include/uapi/asm/socket.h b/arch/alpha/include/uapi/asm/socket.h
index 946a5fad2691..bb3d534826bb 100644
--- a/arch/alpha/include/uapi/asm/socket.h
+++ b/arch/alpha/include/uapi/asm/socket.h
@@ -157,6 +157,8 @@
 
 #define SO_RIGHTS_NOTRUNC      85
 
+#define SO_PASSPIDFD_THREAD    86
+
 #if !defined(__KERNEL__)
 
 #if __BITS_PER_LONG == 64
diff --git a/arch/mips/include/uapi/asm/socket.h b/arch/mips/include/uapi/asm/socket.h
index f1641dde135f..269badcaa086 100644
--- a/arch/mips/include/uapi/asm/socket.h
+++ b/arch/mips/include/uapi/asm/socket.h
@@ -168,6 +168,8 @@
 
 #define SO_RIGHTS_NOTRUNC      85
 
+#define SO_PASSPIDFD_THREAD    86
+
 #if !defined(__KERNEL__)
 
 #if __BITS_PER_LONG == 64
diff --git a/arch/parisc/include/uapi/asm/socket.h b/arch/parisc/include/uapi/asm/socket.h
index f3a3815c7dc2..313aee10a52c 100644
--- a/arch/parisc/include/uapi/asm/socket.h
+++ b/arch/parisc/include/uapi/asm/socket.h
@@ -149,6 +149,8 @@
 
 #define SO_RIGHTS_NOTRUNC	0x4053
 
+#define SO_PASSPIDFD_THREAD	0x4054
+
 #if !defined(__KERNEL__)
 
 #if __BITS_PER_LONG == 64
diff --git a/arch/sparc/include/uapi/asm/socket.h b/arch/sparc/include/uapi/asm/socket.h
index 7907f3b1f0ee..bd3e69bcce7a 100644
--- a/arch/sparc/include/uapi/asm/socket.h
+++ b/arch/sparc/include/uapi/asm/socket.h
@@ -150,6 +150,8 @@
 
 #define SO_RIGHTS_NOTRUNC        0x005e
 
+#define SO_PASSPIDFD_THREAD      0x005f
+
 #if !defined(__KERNEL__)
 
 
diff --git a/include/net/sock.h b/include/net/sock.h
index 51185222aac2..fc09c92e8a83 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -356,6 +356,7 @@ struct sk_filter;
   *	@sk_scm_security: flagged by SO_PASSSEC to recv SCM_SECURITY
   *	@sk_scm_pidfd: flagged by SO_PASSPIDFD to recv SCM_PIDFD
   *	@sk_scm_rights: flagged by SO_PASSRIGHTS to recv SCM_RIGHTS
+  *	@sk_scm_pidfd_thread: flagged by SO_PASSPIDFD_THREAD to recv a thread SCM_PIDFD
   *	@sk_scm_unused: unused flags for scm_recv()
   *	@ns_tracker: tracker for netns reference
   *	@sk_user_frags: xarray of pages the user is holding a reference on.
@@ -562,7 +563,8 @@ struct sock {
 				sk_scm_security : 1,
 				sk_scm_pidfd : 1,
 				sk_scm_rights : 1,
-				sk_scm_unused : 4;
+				sk_scm_pidfd_thread : 1,
+				sk_scm_unused : 3;
 		};
 	};
 	u8			sk_clockid;
@@ -2986,6 +2988,12 @@ static inline bool sk_is_stream_unix(const struct sock *sk)
 	return sk_is_unix(sk) && sk->sk_type == SOCK_STREAM;
 }
 
+/* SO_PASSPIDFD or SO_PASSPIDFD_THREAD asked for an SCM_PIDFD. */
+static inline bool sk_scm_pidfd_wanted(const struct sock *sk)
+{
+	return sk->sk_scm_pidfd || sk->sk_scm_pidfd_thread;
+}
+
 static inline bool sk_is_vsock(const struct sock *sk)
 {
 	return sk->sk_family == AF_VSOCK;
diff --git a/include/uapi/asm-generic/socket.h b/include/uapi/asm-generic/socket.h
index 84ea7b92936e..d1e5c6de146d 100644
--- a/include/uapi/asm-generic/socket.h
+++ b/include/uapi/asm-generic/socket.h
@@ -152,6 +152,8 @@
 
 #define SO_RIGHTS_NOTRUNC	85
 
+#define SO_PASSPIDFD_THREAD	86
+
 #if !defined(__KERNEL__)
 
 #if __BITS_PER_LONG == 64 || (defined(__x86_64__) && defined(__ILP32__))
diff --git a/net/core/scm.c b/net/core/scm.c
index 9b9e119c353a..d69768414af4 100644
--- a/net/core/scm.c
+++ b/net/core/scm.c
@@ -499,9 +499,13 @@ static bool scm_has_secdata(struct sock *sk)
 }
 #endif
 
-static void scm_pidfd_recv(struct msghdr *msg, struct scm_cookie *scm)
+static void scm_pidfd_recv(struct sock *sk, struct msghdr *msg,
+			   struct scm_cookie *scm)
 {
+	enum pid_type type = sk->sk_scm_pidfd_thread ? PIDTYPE_PID : PIDTYPE_TGID;
+	struct pid *pid = scm->pid[type];
 	struct file *pidfd_file = NULL;
+	unsigned int flags = PIDFD_STALE;
 	int len, pidfd;
 
 	/* put_cmsg() doesn't return an error if CMSG is truncated,
@@ -517,10 +521,13 @@ static void scm_pidfd_recv(struct msghdr *msg, struct scm_cookie *scm)
 		return;
 	}
 
-	if (!scm->pid[PIDTYPE_TGID])
+	if (!pid)
 		return;
 
-	pidfd = pidfd_prepare(scm->pid[PIDTYPE_TGID], PIDFD_STALE, &pidfd_file);
+	if (type == PIDTYPE_PID)
+		flags |= PIDFD_THREAD;
+
+	pidfd = pidfd_prepare(pid, flags, &pidfd_file);
 
 	if (put_cmsg(msg, SOL_SOCKET, SCM_PIDFD, sizeof(int), &pidfd)) {
 		if (pidfd_file) {
@@ -539,7 +546,7 @@ static bool __scm_recv_common(struct sock *sk, struct msghdr *msg,
 			      struct scm_cookie *scm, int flags)
 {
 	if (!msg->msg_control) {
-		if (sk->sk_scm_credentials || sk->sk_scm_pidfd ||
+		if (sk->sk_scm_credentials || sk_scm_pidfd_wanted(sk) ||
 		    scm->fp || scm_has_secdata(sk))
 			msg->msg_flags |= MSG_CTRUNC;
 
@@ -586,8 +593,8 @@ void scm_recv_unix(struct socket *sock, struct msghdr *msg,
 		scm_detach_fds(msg, scm, READ_ONCE(u->scm_rights_notrunc));
 	}
 
-	if (sock->sk->sk_scm_pidfd)
-		scm_pidfd_recv(msg, scm);
+	if (sk_scm_pidfd_wanted(sock->sk))
+		scm_pidfd_recv(sock->sk, msg, scm);
 
 	scm_destroy_cred(scm);
 }
diff --git a/net/core/sock.c b/net/core/sock.c
index 1ad41904db25..f9615b0de10e 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -1571,10 +1571,25 @@ int sk_setsockopt(struct sock *sk, int level, int optname,
 		break;
 
 	case SO_PASSPIDFD:
-		if (sk_is_unix(sk))
+		if (sk_is_unix(sk)) {
+			/* Mutually exclusive with SO_PASSPIDFD_THREAD. */
 			sk->sk_scm_pidfd = valbool;
-		else
+			if (valbool)
+				sk->sk_scm_pidfd_thread = 0;
+		} else {
+			ret = -EOPNOTSUPP;
+		}
+		break;
+
+	case SO_PASSPIDFD_THREAD:
+		if (sk_is_unix(sk)) {
+			/* Mutually exclusive with SO_PASSPIDFD. */
+			sk->sk_scm_pidfd_thread = valbool;
+			if (valbool)
+				sk->sk_scm_pidfd = 0;
+		} else {
 			ret = -EOPNOTSUPP;
+		}
 		break;
 
 	case SO_PASSRIGHTS:
@@ -1892,6 +1907,13 @@ int sk_getsockopt(struct sock *sk, int level, int optname,
 		v.val = sk->sk_scm_pidfd;
 		break;
 
+	case SO_PASSPIDFD_THREAD:
+		if (!sk_is_unix(sk))
+			return -EOPNOTSUPP;
+
+		v.val = sk->sk_scm_pidfd_thread;
+		break;
+
 	case SO_PASSRIGHTS:
 		if (!sk_is_unix(sk))
 			return -EOPNOTSUPP;
diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 011af84e3626..468a9c479b87 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -803,7 +803,7 @@ static void copy_peercred(struct sock *sk, struct sock *peersk)
 
 static bool unix_may_passcred(const struct sock *sk)
 {
-	return sk->sk_scm_credentials || sk->sk_scm_pidfd;
+	return sk->sk_scm_credentials || sk_scm_pidfd_wanted(sk);
 }
 
 static int unix_listen(struct socket *sock, int backlog)
@@ -2048,9 +2048,14 @@ static int unix_maybe_add_creds(struct sk_buff *skb, const struct sock *sk,
 	return 0;
 }
 
-static bool unix_skb_scm_eq(struct sk_buff *skb,
+static bool unix_skb_scm_eq(const struct sock *sk, struct sk_buff *skb,
 			    struct scm_cookie *scm)
 {
+	/* Only a thread pidfd receiver can tell threads of one process apart. */
+	if (sk->sk_scm_pidfd_thread &&
+	    UNIXCB(skb).pid[PIDTYPE_PID] != scm->pid[PIDTYPE_PID])
+		return false;
+
 	return UNIXCB(skb).pid[PIDTYPE_TGID] == scm->pid[PIDTYPE_TGID] &&
 	       uid_eq(UNIXCB(skb).uid, scm->creds.uid) &&
 	       gid_eq(UNIXCB(skb).gid, scm->creds.gid) &&
@@ -3029,7 +3034,7 @@ static int unix_stream_read_generic(struct unix_stream_read_state *state,
 
 		if (check_creds) {
 			/* Never glue messages from different writers */
-			if (!unix_skb_scm_eq(skb, &scm))
+			if (!unix_skb_scm_eq(sk, skb, &scm))
 				break;
 		} else if (unix_may_passcred(sk)) {
 			/* Copy credentials */

-- 
2.53.0

[PATCH 04/10] selftests/net: SO_PASSPIDFD_THREAD

[Christian Brauner]

Extend the af_unix scm_pidfd selftest with SO_PASSPIDFD_THREAD tests.

Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
---
 tools/testing/selftests/net/af_unix/Makefile    |   2 +
 tools/testing/selftests/net/af_unix/scm_pidfd.c | 269 ++++++++++++++++++++++++
 2 files changed, 271 insertions(+)

diff --git a/tools/testing/selftests/net/af_unix/Makefile b/tools/testing/selftests/net/af_unix/Makefile
index a66f10fb0c23..45b841758f1b 100644
--- a/tools/testing/selftests/net/af_unix/Makefile
+++ b/tools/testing/selftests/net/af_unix/Makefile
@@ -23,6 +23,8 @@ TEST_GEN_FILES := scm_rights_denial_lsm.bpf.o
 include ../../lib.mk
 include ../bpf.mk
 
+$(OUTPUT)/scm_pidfd: CFLAGS += -pthread
+
 $(OUTPUT)/scm_rights_denial_lsm: $(BPFOBJ)
 $(OUTPUT)/scm_rights_denial_lsm: CFLAGS += -I$(SCRATCH_DIR)/include
 $(OUTPUT)/scm_rights_denial_lsm: LDLIBS += -lelf -lz
diff --git a/tools/testing/selftests/net/af_unix/scm_pidfd.c b/tools/testing/selftests/net/af_unix/scm_pidfd.c
index 2c18b92a2603..019c48e1cdcd 100644
--- a/tools/testing/selftests/net/af_unix/scm_pidfd.c
+++ b/tools/testing/selftests/net/af_unix/scm_pidfd.c
@@ -10,6 +10,7 @@
 #include <unistd.h>
 #include <string.h>
 #include <errno.h>
+#include <pthread.h>
 #include <sys/un.h>
 #include <sys/signal.h>
 #include <sys/types.h>
@@ -27,6 +28,10 @@
 #define SCM_PIDFD 0x04
 #endif
 
+#ifndef SO_PASSPIDFD_THREAD
+#define SO_PASSPIDFD_THREAD 86
+#endif
+
 #define CHILD_EXIT_CODE_OK 123
 
 static void child_die()
@@ -553,4 +558,268 @@ TEST_F(scm_pidfd, test)
 	close(pfd);
 }
 
+struct thread_ids {
+	pid_t pid;
+	pid_t tid;
+};
+
+static void *send_ids_thread(void *arg)
+{
+	int fd = *(int *)arg;
+	struct thread_ids ids = {
+		.pid = getpid(),
+		.tid = gettid(),
+	};
+	char sync;
+
+	if (send(fd, &ids, sizeof(ids), 0) != sizeof(ids))
+		return (void *)1;
+
+	/* stay alive until the receiver has looked at our pidfd */
+	if (read(fd, &sync, 1) != 1)
+		return (void *)1;
+
+	return NULL;
+}
+
+static void *send_ids_creds_thread(void *arg)
+{
+	int fd = *(int *)arg;
+	struct thread_ids ids = {
+		.pid = getpid(),
+		.tid = gettid(),
+	};
+	struct ucred ucred = {
+		.pid = getpid(),
+		.uid = getuid(),
+		.gid = getgid(),
+	};
+	char control[CMSG_SPACE(sizeof(ucred))] = { 0 };
+	struct iovec iov;
+	struct msghdr msg = { 0 };
+	struct cmsghdr *cmsg;
+	char sync;
+
+	iov.iov_base = &ids;
+	iov.iov_len = sizeof(ids);
+
+	msg.msg_iov = &iov;
+	msg.msg_iovlen = 1;
+	msg.msg_control = control;
+	msg.msg_controllen = sizeof(control);
+
+	cmsg = CMSG_FIRSTHDR(&msg);
+	cmsg->cmsg_level = SOL_SOCKET;
+	cmsg->cmsg_type = SCM_CREDENTIALS;
+	cmsg->cmsg_len = CMSG_LEN(sizeof(ucred));
+	memcpy(CMSG_DATA(cmsg), &ucred, sizeof(ucred));
+
+	if (sendmsg(fd, &msg, 0) != sizeof(ids))
+		return (void *)1;
+
+	if (read(fd, &sync, 1) != 1)
+		return (void *)1;
+
+	return NULL;
+}
+
+static void thread_client(int fd, int syncfd, void *(*sender)(void *))
+{
+	pthread_t thread;
+	void *ret;
+	char sync;
+
+	/* wait until the receiver enabled SO_PASSPIDFD */
+	if (read(syncfd, &sync, 1) != 1)
+		child_die();
+
+	if (pthread_create(&thread, NULL, sender, &fd))
+		child_die();
+
+	if (pthread_join(thread, &ret) || ret)
+		child_die();
+
+	exit(0);
+}
+
+static int recv_pidfd(int fd, struct thread_ids *ids)
+{
+	char control[CMSG_SPACE(sizeof(int))] = { 0 };
+	struct iovec iov;
+	struct msghdr msg = { 0 };
+	struct cmsghdr *cmsg;
+	int pidfd = -1;
+
+	iov.iov_base = ids;
+	iov.iov_len = sizeof(*ids);
+
+	msg.msg_iov = &iov;
+	msg.msg_iovlen = 1;
+	msg.msg_control = control;
+	msg.msg_controllen = sizeof(control);
+
+	if (recvmsg(fd, &msg, 0) != sizeof(*ids)) {
+		log_err("recvmsg");
+		return -1;
+	}
+
+	if (msg.msg_flags & (MSG_TRUNC | MSG_CTRUNC)) {
+		log_err("recvmsg: truncated");
+		return -1;
+	}
+
+	for (cmsg = CMSG_FIRSTHDR(&msg); cmsg != NULL;
+	     cmsg = CMSG_NXTHDR(&msg, cmsg)) {
+		if (cmsg->cmsg_level == SOL_SOCKET &&
+		    cmsg->cmsg_type == SCM_PIDFD)
+			memcpy(&pidfd, CMSG_DATA(cmsg), sizeof(pidfd));
+	}
+
+	return pidfd;
+}
+
+static int thread_pidfd_flow(void *(*sender)(void *), int optname,
+			     struct thread_ids *ids, struct pidfd_info *info)
+{
+	int sk[2];
+	int syncpipe[2];
+	int pidfd;
+	int child_status = 0;
+	pid_t child;
+
+	if (socketpair(AF_UNIX, SOCK_STREAM, 0, sk))
+		return -1;
+
+	if (pipe(syncpipe))
+		return -1;
+
+	child = fork();
+	if (child < 0)
+		return -1;
+
+	if (child == 0) {
+		close(sk[0]);
+		close(syncpipe[1]);
+		thread_client(sk[1], syncpipe[0], sender);
+	}
+	close(sk[1]);
+	close(syncpipe[0]);
+
+	int on = 1;
+
+	if (setsockopt(sk[0], SOL_SOCKET, optname, &on, sizeof(on))) {
+		log_err("Failed to set pidfd passing option");
+		return -1;
+	}
+
+	if (write(syncpipe[1], "1", 1) != 1)
+		return -1;
+	close(syncpipe[1]);
+
+	pidfd = recv_pidfd(sk[0], ids);
+	if (pidfd < 0)
+		return -1;
+
+	info->mask = PIDFD_INFO_PID;
+	if (ioctl(pidfd, PIDFD_GET_INFO, info)) {
+		log_err("ioctl(PIDFD_GET_INFO)");
+		close(pidfd);
+		return -1;
+	}
+	close(pidfd);
+
+	/* release the sending thread */
+	if (write(sk[0], "x", 1) != 1)
+		return -1;
+	close(sk[0]);
+
+	waitpid(child, &child_status, 0);
+	if (!WIFEXITED(child_status) || WEXITSTATUS(child_status))
+		return -1;
+
+	return 0;
+}
+
+static int sockopt_set(int fd, int optname, int val)
+{
+	return setsockopt(fd, SOL_SOCKET, optname, &val, sizeof(val));
+}
+
+static int sockopt_get(int fd, int optname)
+{
+	socklen_t len = sizeof(int);
+	int val = -1;
+
+	if (getsockopt(fd, SOL_SOCKET, optname, &val, &len))
+		return -1;
+
+	return val;
+}
+
+TEST(scm_pidfd_setsockopt_values)
+{
+	int sk[2];
+
+	ASSERT_EQ(0, socketpair(AF_UNIX, SOCK_STREAM, 0, sk));
+
+	ASSERT_EQ(0, sockopt_set(sk[0], SO_PASSPIDFD_THREAD, 1));
+	ASSERT_EQ(1, sockopt_get(sk[0], SO_PASSPIDFD_THREAD));
+	ASSERT_EQ(0, sockopt_get(sk[0], SO_PASSPIDFD));
+
+	/* The option set last wins. */
+	ASSERT_EQ(0, sockopt_set(sk[0], SO_PASSPIDFD, 1));
+	ASSERT_EQ(1, sockopt_get(sk[0], SO_PASSPIDFD));
+	ASSERT_EQ(0, sockopt_get(sk[0], SO_PASSPIDFD_THREAD));
+
+	ASSERT_EQ(0, sockopt_set(sk[0], SO_PASSPIDFD_THREAD, 1));
+	ASSERT_EQ(1, sockopt_get(sk[0], SO_PASSPIDFD_THREAD));
+	ASSERT_EQ(0, sockopt_get(sk[0], SO_PASSPIDFD));
+
+	/* Disabling one option leaves the other alone. */
+	ASSERT_EQ(0, sockopt_set(sk[0], SO_PASSPIDFD, 0));
+	ASSERT_EQ(1, sockopt_get(sk[0], SO_PASSPIDFD_THREAD));
+	ASSERT_EQ(0, sockopt_set(sk[0], SO_PASSPIDFD_THREAD, 0));
+	ASSERT_EQ(0, sockopt_get(sk[0], SO_PASSPIDFD));
+	ASSERT_EQ(0, sockopt_get(sk[0], SO_PASSPIDFD_THREAD));
+
+	close(sk[0]);
+	close(sk[1]);
+}
+
+TEST(scm_pidfd_thread)
+{
+	struct thread_ids ids;
+	struct pidfd_info info;
+
+	ASSERT_EQ(0, thread_pidfd_flow(send_ids_thread, SO_PASSPIDFD_THREAD,
+				       &ids, &info));
+	ASSERT_NE(ids.pid, ids.tid);
+	EXPECT_EQ(ids.tid, info.pid);
+	EXPECT_EQ(ids.pid, info.tgid);
+}
+
+TEST(scm_pidfd_thread_group)
+{
+	struct thread_ids ids;
+	struct pidfd_info info;
+
+	ASSERT_EQ(0, thread_pidfd_flow(send_ids_thread, SO_PASSPIDFD,
+				       &ids, &info));
+	ASSERT_NE(ids.pid, ids.tid);
+	EXPECT_EQ(ids.pid, info.pid);
+	EXPECT_EQ(ids.pid, info.tgid);
+}
+
+TEST(scm_pidfd_thread_creds)
+{
+	struct thread_ids ids;
+	struct pidfd_info info;
+
+	ASSERT_EQ(0, thread_pidfd_flow(send_ids_creds_thread, SO_PASSPIDFD_THREAD,
+				       &ids, &info));
+	ASSERT_NE(ids.pid, ids.tid);
+	EXPECT_EQ(ids.tid, info.pid);
+	EXPECT_EQ(ids.pid, info.tgid);
+}
+
 TEST_HARNESS_MAIN

-- 
2.53.0

[PATCH 05/10] net: turn sk_peer_pid into an array indexed by pid type

[Christian Brauner]

Currently only the struct pid of the thread-group leader is recorded
for a socket's peer. To make room for the struct pid of the thread that
called connect(), listen() or socketpair() turn sk_peer_pid into an
array indexed by pid type. All users, including bluetooth and the
coredump socket, keep using the PIDTYPE_TGID slot.

Nothing fills the PIDTYPE_PID slot yet. No functional changes.

Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
---
 fs/coredump.c                |  2 +-
 include/net/sock.h           |  4 ++--
 net/bluetooth/af_bluetooth.c |  6 +++---
 net/bluetooth/hci_sock.c     |  8 ++++----
 net/bluetooth/l2cap_sock.c   |  2 +-
 net/core/sock.c              |  9 +++++----
 net/unix/af_unix.c           | 14 +++++++-------
 7 files changed, 23 insertions(+), 22 deletions(-)

diff --git a/fs/coredump.c b/fs/coredump.c
index ac3cd74808c6..71a0093ada1b 100644
--- a/fs/coredump.c
+++ b/fs/coredump.c
@@ -722,7 +722,7 @@ static bool coredump_sock_connect(struct core_name *cn, struct coredump_params *
 	}
 
 	/* ... and validate that @sk_peer_pid matches @cprm.pid. */
-	if (WARN_ON_ONCE(unix_peer(socket->sk)->sk_peer_pid != cprm->pid))
+	if (WARN_ON_ONCE(unix_peer(socket->sk)->sk_peer_pid[PIDTYPE_TGID] != cprm->pid))
 		return false;
 
 	cprm->limit = RLIM_INFINITY;
diff --git a/include/net/sock.h b/include/net/sock.h
index fc09c92e8a83..67b743bab220 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -301,7 +301,7 @@ struct sk_filter;
   *	@sk_type: socket type (%SOCK_STREAM, etc)
   *	@sk_protocol: which protocol this socket belongs in this network family
   *	@sk_peer_lock: lock protecting @sk_peer_pid and @sk_peer_cred
-  *	@sk_peer_pid: &struct pid for this socket's peer
+  *	@sk_peer_pid: &struct pid for this socket's peer, by pid type
   *	@sk_peer_cred: %SO_PEERCRED setting
   *	@sk_rcvlowat: %SO_RCVLOWAT setting
   *	@sk_rcvtimeo: %SO_RCVTIMEO setting
@@ -546,7 +546,7 @@ struct sock {
 	u64			sk_ino;
 	spinlock_t		sk_peer_lock;
 	int			sk_bind_phc;
-	struct pid		*sk_peer_pid;
+	DECLARE_PIDS(sk_peer_pid, PIDTYPE_TGID);
 	const struct cred	*sk_peer_cred;
 
 	ktime_t			sk_stamp;
diff --git a/net/bluetooth/af_bluetooth.c b/net/bluetooth/af_bluetooth.c
index 411d66f24393..7758e9ea3848 100644
--- a/net/bluetooth/af_bluetooth.c
+++ b/net/bluetooth/af_bluetooth.c
@@ -161,7 +161,7 @@ struct sock *bt_sock_alloc(struct net *net, struct socket *sock,
 	/* Init peer information so it can be properly monitored */
 	if (!kern) {
 		spin_lock(&sk->sk_peer_lock);
-		sk->sk_peer_pid  = get_pid(task_tgid(current));
+		sk->sk_peer_pid[PIDTYPE_TGID]  = get_pid(task_tgid(current));
 		sk->sk_peer_cred = get_current_cred();
 		spin_unlock(&sk->sk_peer_lock);
 	}
@@ -235,9 +235,9 @@ void bt_accept_enqueue(struct sock *parent, struct sock *sk, bool bh)
 	 * socket is allocated by the kernel.
 	 */
 	spin_lock(&sk->sk_peer_lock);
-	old_pid = sk->sk_peer_pid;
+	old_pid = sk->sk_peer_pid[PIDTYPE_TGID];
 	old_cred = sk->sk_peer_cred;
-	sk->sk_peer_pid = get_pid(parent->sk_peer_pid);
+	sk->sk_peer_pid[PIDTYPE_TGID] = get_pid(parent->sk_peer_pid[PIDTYPE_TGID]);
 	sk->sk_peer_cred = get_cred(parent->sk_peer_cred);
 	spin_unlock(&sk->sk_peer_lock);
 
diff --git a/net/bluetooth/hci_sock.c b/net/bluetooth/hci_sock.c
index 070ca388f9ac..91e4738eabdb 100644
--- a/net/bluetooth/hci_sock.c
+++ b/net/bluetooth/hci_sock.c
@@ -273,21 +273,21 @@ static void hci_sock_copy_creds(struct sock *sk, struct sk_buff *skb)
 	creds = &bt_cb(skb)->creds;
 
 	/* Check if peer credentials is set */
-	if (!sk->sk_peer_pid) {
+	if (!sk->sk_peer_pid[PIDTYPE_TGID]) {
 		/* Check if parent peer credentials is set */
-		if (bt_sk(sk)->parent && bt_sk(sk)->parent->sk_peer_pid)
+		if (bt_sk(sk)->parent && bt_sk(sk)->parent->sk_peer_pid[PIDTYPE_TGID])
 			sk = bt_sk(sk)->parent;
 		else
 			return;
 	}
 
 	/* Check if scm_creds already set */
-	if (creds->pid == pid_vnr(sk->sk_peer_pid))
+	if (creds->pid == pid_vnr(sk->sk_peer_pid[PIDTYPE_TGID]))
 		return;
 
 	memset(creds, 0, sizeof(*creds));
 
-	creds->pid = pid_vnr(sk->sk_peer_pid);
+	creds->pid = pid_vnr(sk->sk_peer_pid[PIDTYPE_TGID]);
 	if (sk->sk_peer_cred) {
 		creds->uid = sk->sk_peer_cred->uid;
 		creds->gid = sk->sk_peer_cred->gid;
diff --git a/net/bluetooth/l2cap_sock.c b/net/bluetooth/l2cap_sock.c
index 1194c37e466f..872d8fb31b6f 100644
--- a/net/bluetooth/l2cap_sock.c
+++ b/net/bluetooth/l2cap_sock.c
@@ -1890,7 +1890,7 @@ static struct pid *l2cap_sock_get_peer_pid_cb(struct l2cap_chan *chan)
 {
 	struct sock *sk = chan->data;
 
-	return sk->sk_peer_pid;
+	return sk->sk_peer_pid[PIDTYPE_TGID];
 }
 
 static void l2cap_sock_suspend_cb(struct l2cap_chan *chan)
diff --git a/net/core/sock.c b/net/core/sock.c
index f9615b0de10e..6ada7e7eb7d7 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -1928,7 +1928,8 @@ int sk_getsockopt(struct sock *sk, int level, int optname,
 			len = sizeof(peercred);
 
 		spin_lock(&sk->sk_peer_lock);
-		cred_to_ucred(sk->sk_peer_pid, sk->sk_peer_cred, &peercred);
+		cred_to_ucred(sk->sk_peer_pid[PIDTYPE_TGID], sk->sk_peer_cred,
+			      &peercred);
 		spin_unlock(&sk->sk_peer_lock);
 
 		if (copy_to_sockptr(optval, &peercred, len))
@@ -1947,7 +1948,7 @@ int sk_getsockopt(struct sock *sk, int level, int optname,
 			len = sizeof(pidfd);
 
 		spin_lock(&sk->sk_peer_lock);
-		peer_pid = get_pid(sk->sk_peer_pid);
+		peer_pid = get_pid(sk->sk_peer_pid[PIDTYPE_TGID]);
 		spin_unlock(&sk->sk_peer_lock);
 
 		if (!peer_pid)
@@ -2401,7 +2402,7 @@ static void __sk_destruct(struct rcu_head *head)
 
 	/* We do not need to acquire sk->sk_peer_lock, we are the last user. */
 	put_cred(sk->sk_peer_cred);
-	put_pid(sk->sk_peer_pid);
+	put_pids(sk->sk_peer_pid);
 
 	if (likely(sk->sk_net_refcnt)) {
 		put_net_track(net, &sk->ns_tracker);
@@ -3797,7 +3798,7 @@ void sock_init_data_uid(struct socket *sock, struct sock *sk, kuid_t uid)
 	sk->sk_frag.offset	=	0;
 	sk->sk_peek_off		=	-1;
 
-	sk->sk_peer_pid 	=	NULL;
+	memset(sk->sk_peer_pid, 0, sizeof(sk->sk_peer_pid));
 	sk->sk_peer_cred	=	NULL;
 	spin_lock_init(&sk->sk_peer_lock);
 
diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 468a9c479b87..335abd23c9bf 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -737,7 +737,7 @@ static void unix_release_sock(struct sock *sk, int embrion)
 }
 
 struct unix_peercred {
-	struct pid *peer_pid;
+	DECLARE_PIDS(peer_pid, PIDTYPE_TGID);
 	const struct cred *peer_cred;
 };
 
@@ -749,7 +749,7 @@ static inline int prepare_peercred(struct unix_peercred *peercred)
 	pid = task_tgid(current);
 	err = pidfs_register_pid(pid);
 	if (likely(!err)) {
-		peercred->peer_pid = get_pid(pid);
+		peercred->peer_pid[PIDTYPE_TGID] = get_pid(pid);
 		peercred->peer_cred = get_current_cred();
 	}
 	return err;
@@ -762,7 +762,7 @@ static void drop_peercred(struct unix_peercred *peercred)
 
 	might_sleep();
 
-	swap(peercred->peer_pid, pid);
+	swap(peercred->peer_pid[PIDTYPE_TGID], pid);
 	swap(peercred->peer_cred, cred);
 
 	put_pid(pid);
@@ -772,7 +772,7 @@ static void drop_peercred(struct unix_peercred *peercred)
 static inline void init_peercred(struct sock *sk,
 				 const struct unix_peercred *peercred)
 {
-	sk->sk_peer_pid = peercred->peer_pid;
+	sk->sk_peer_pid[PIDTYPE_TGID] = peercred->peer_pid[PIDTYPE_TGID];
 	sk->sk_peer_cred = peercred->peer_cred;
 }
 
@@ -782,12 +782,12 @@ static void update_peercred(struct sock *sk, struct unix_peercred *peercred)
 	struct pid *old_pid;
 
 	spin_lock(&sk->sk_peer_lock);
-	old_pid = sk->sk_peer_pid;
+	old_pid = sk->sk_peer_pid[PIDTYPE_TGID];
 	old_cred = sk->sk_peer_cred;
 	init_peercred(sk, peercred);
 	spin_unlock(&sk->sk_peer_lock);
 
-	peercred->peer_pid = old_pid;
+	peercred->peer_pid[PIDTYPE_TGID] = old_pid;
 	peercred->peer_cred = old_cred;
 }
 
@@ -796,7 +796,7 @@ static void copy_peercred(struct sock *sk, struct sock *peersk)
 	lockdep_assert_held(&unix_sk(peersk)->lock);
 
 	spin_lock(&sk->sk_peer_lock);
-	sk->sk_peer_pid = get_pid(peersk->sk_peer_pid);
+	sk->sk_peer_pid[PIDTYPE_TGID] = get_pid(peersk->sk_peer_pid[PIDTYPE_TGID]);
 	sk->sk_peer_cred = get_cred(peersk->sk_peer_cred);
 	spin_unlock(&sk->sk_peer_lock);
 }

-- 
2.53.0

[PATCH 06/10] af_unix: record the pid of the connecting thread

[Christian Brauner]

Currently only the struct pid of the thread-group leader is recorded.
The identity of the actual thread that connected to a given socket
cannot be retrieved.

Add the plumbing to make it possible to retrieve a pidfd for the
connecting thread. Nothing uses the thread-specific struct pid yet. No
functional changes.

Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
---
 net/unix/af_unix.c | 30 +++++++++++++-----------------
 1 file changed, 13 insertions(+), 17 deletions(-)

diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 335abd23c9bf..d01ee76c8026 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -743,51 +743,47 @@ struct unix_peercred {
 
 static inline int prepare_peercred(struct unix_peercred *peercred)
 {
-	struct pid *pid;
 	int err;
 
-	pid = task_tgid(current);
-	err = pidfs_register_pid(pid);
-	if (likely(!err)) {
-		peercred->peer_pid[PIDTYPE_TGID] = get_pid(pid);
-		peercred->peer_cred = get_current_cred();
+	get_task_pids(peercred->peer_pid, current);
+	err = pidfs_register_pids(peercred->peer_pid);
+	if (unlikely(err)) {
+		put_pids(peercred->peer_pid);
+		return err;
 	}
-	return err;
+
+	peercred->peer_cred = get_current_cred();
+	return 0;
 }
 
 static void drop_peercred(struct unix_peercred *peercred)
 {
 	const struct cred *cred = NULL;
-	struct pid *pid = NULL;
 
 	might_sleep();
 
-	swap(peercred->peer_pid[PIDTYPE_TGID], pid);
+	put_pids(peercred->peer_pid);
 	swap(peercred->peer_cred, cred);
-
-	put_pid(pid);
 	put_cred(cred);
 }
 
 static inline void init_peercred(struct sock *sk,
 				 const struct unix_peercred *peercred)
 {
-	sk->sk_peer_pid[PIDTYPE_TGID] = peercred->peer_pid[PIDTYPE_TGID];
+	memcpy(sk->sk_peer_pid, peercred->peer_pid, sizeof(sk->sk_peer_pid));
 	sk->sk_peer_cred = peercred->peer_cred;
 }
 
 static void update_peercred(struct sock *sk, struct unix_peercred *peercred)
 {
 	const struct cred *old_cred;
-	struct pid *old_pid;
 
 	spin_lock(&sk->sk_peer_lock);
-	old_pid = sk->sk_peer_pid[PIDTYPE_TGID];
+	swap_pids(sk->sk_peer_pid, peercred->peer_pid);
 	old_cred = sk->sk_peer_cred;
-	init_peercred(sk, peercred);
+	sk->sk_peer_cred = peercred->peer_cred;
 	spin_unlock(&sk->sk_peer_lock);
 
-	peercred->peer_pid[PIDTYPE_TGID] = old_pid;
 	peercred->peer_cred = old_cred;
 }
 
@@ -796,7 +792,7 @@ static void copy_peercred(struct sock *sk, struct sock *peersk)
 	lockdep_assert_held(&unix_sk(peersk)->lock);
 
 	spin_lock(&sk->sk_peer_lock);
-	sk->sk_peer_pid[PIDTYPE_TGID] = get_pid(peersk->sk_peer_pid[PIDTYPE_TGID]);
+	get_pids(sk->sk_peer_pid, peersk->sk_peer_pid);
 	sk->sk_peer_cred = get_cred(peersk->sk_peer_cred);
 	spin_unlock(&sk->sk_peer_lock);
 }

-- 
2.53.0

[PATCH 07/10] net: add SO_PEERPIDFD_THREAD to get a thread-specific pidfd

[Christian Brauner]

SO_PEERPIDFD hands out a pidfd for the thread-group that called
connect() or socketpair(). Enable workloads such as the coredump server
or a broker to get a pidfd of the specific thread that connected to the
socket.

Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
---
 arch/alpha/include/uapi/asm/socket.h  |  2 +
 arch/mips/include/uapi/asm/socket.h   |  2 +
 arch/parisc/include/uapi/asm/socket.h |  2 +
 arch/sparc/include/uapi/asm/socket.h  |  2 +
 include/uapi/asm-generic/socket.h     |  2 +
 net/core/sock.c                       | 87 ++++++++++++++++++++---------------
 net/unix/af_unix.c                    |  1 +
 7 files changed, 61 insertions(+), 37 deletions(-)

diff --git a/arch/alpha/include/uapi/asm/socket.h b/arch/alpha/include/uapi/asm/socket.h
index bb3d534826bb..5d3524c26b2b 100644
--- a/arch/alpha/include/uapi/asm/socket.h
+++ b/arch/alpha/include/uapi/asm/socket.h
@@ -159,6 +159,8 @@
 
 #define SO_PASSPIDFD_THREAD    86
 
+#define SO_PEERPIDFD_THREAD    87
+
 #if !defined(__KERNEL__)
 
 #if __BITS_PER_LONG == 64
diff --git a/arch/mips/include/uapi/asm/socket.h b/arch/mips/include/uapi/asm/socket.h
index 269badcaa086..245a43f52fb1 100644
--- a/arch/mips/include/uapi/asm/socket.h
+++ b/arch/mips/include/uapi/asm/socket.h
@@ -170,6 +170,8 @@
 
 #define SO_PASSPIDFD_THREAD    86
 
+#define SO_PEERPIDFD_THREAD    87
+
 #if !defined(__KERNEL__)
 
 #if __BITS_PER_LONG == 64
diff --git a/arch/parisc/include/uapi/asm/socket.h b/arch/parisc/include/uapi/asm/socket.h
index 313aee10a52c..f23710e1c671 100644
--- a/arch/parisc/include/uapi/asm/socket.h
+++ b/arch/parisc/include/uapi/asm/socket.h
@@ -151,6 +151,8 @@
 
 #define SO_PASSPIDFD_THREAD	0x4054
 
+#define SO_PEERPIDFD_THREAD	0x4055
+
 #if !defined(__KERNEL__)
 
 #if __BITS_PER_LONG == 64
diff --git a/arch/sparc/include/uapi/asm/socket.h b/arch/sparc/include/uapi/asm/socket.h
index bd3e69bcce7a..b35b25bdefc2 100644
--- a/arch/sparc/include/uapi/asm/socket.h
+++ b/arch/sparc/include/uapi/asm/socket.h
@@ -152,6 +152,8 @@
 
 #define SO_PASSPIDFD_THREAD      0x005f
 
+#define SO_PEERPIDFD_THREAD      0x0060
+
 #if !defined(__KERNEL__)
 
 
diff --git a/include/uapi/asm-generic/socket.h b/include/uapi/asm-generic/socket.h
index d1e5c6de146d..56fed7ab27ab 100644
--- a/include/uapi/asm-generic/socket.h
+++ b/include/uapi/asm-generic/socket.h
@@ -154,6 +154,8 @@
 
 #define SO_PASSPIDFD_THREAD	86
 
+#define SO_PEERPIDFD_THREAD	87
+
 #if !defined(__KERNEL__)
 
 #if __BITS_PER_LONG == 64 || (defined(__x86_64__) && defined(__ILP32__))
diff --git a/net/core/sock.c b/net/core/sock.c
index 6ada7e7eb7d7..cb2ffd329bc6 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -1743,6 +1743,50 @@ static int groups_to_user(sockptr_t dst, const struct group_info *src)
 	return 0;
 }
 
+/* Hand out a pidfd for @type of the socket's peer via SO_PEERPIDFD*. */
+static int sk_getsockopt_peerpidfd(struct sock *sk, enum pid_type type,
+				   sockptr_t optval, sockptr_t optlen, int len)
+{
+	struct file *pidfd_file = NULL;
+	unsigned int flags = 0;
+	struct pid *peer_pid;
+	int pidfd;
+
+	if (len > sizeof(pidfd))
+		len = sizeof(pidfd);
+
+	spin_lock(&sk->sk_peer_lock);
+	peer_pid = get_pid(sk->sk_peer_pid[type]);
+	spin_unlock(&sk->sk_peer_lock);
+
+	if (!peer_pid)
+		return -ENODATA;
+
+	/* The use of PIDFD_STALE requires stashing of struct pid on pidfs
+	 * with pidfs_register_pid() and only AF_UNIX were prepared for this.
+	 */
+	if (sk->sk_family == AF_UNIX)
+		flags |= PIDFD_STALE;
+	if (type == PIDTYPE_PID)
+		flags |= PIDFD_THREAD;
+
+	pidfd = pidfd_prepare(peer_pid, flags, &pidfd_file);
+	put_pid(peer_pid);
+	if (pidfd < 0)
+		return pidfd;
+
+	if (copy_to_sockptr(optval, &pidfd, len) ||
+	    copy_to_sockptr(optlen, &len, sizeof(int))) {
+		put_unused_fd(pidfd);
+		fput(pidfd_file);
+
+		return -EFAULT;
+	}
+
+	fd_install(pidfd, pidfd_file);
+	return 0;
+}
+
 int sk_getsockopt(struct sock *sk, int level, int optname,
 		  sockptr_t optval, sockptr_t optlen)
 {
@@ -1938,45 +1982,14 @@ int sk_getsockopt(struct sock *sk, int level, int optname,
 	}
 
 	case SO_PEERPIDFD:
-	{
-		struct pid *peer_pid;
-		struct file *pidfd_file = NULL;
-		unsigned int flags = 0;
-		int pidfd;
-
-		if (len > sizeof(pidfd))
-			len = sizeof(pidfd);
-
-		spin_lock(&sk->sk_peer_lock);
-		peer_pid = get_pid(sk->sk_peer_pid[PIDTYPE_TGID]);
-		spin_unlock(&sk->sk_peer_lock);
-
-		if (!peer_pid)
-			return -ENODATA;
-
-		/* The use of PIDFD_STALE requires stashing of struct pid
-		 * on pidfs with pidfs_register_pid() and only AF_UNIX
-		 * were prepared for this.
-		 */
-		if (sk->sk_family == AF_UNIX)
-			flags = PIDFD_STALE;
+		return sk_getsockopt_peerpidfd(sk, PIDTYPE_TGID, optval, optlen, len);
 
-		pidfd = pidfd_prepare(peer_pid, flags, &pidfd_file);
-		put_pid(peer_pid);
-		if (pidfd < 0)
-			return pidfd;
-
-		if (copy_to_sockptr(optval, &pidfd, len) ||
-		    copy_to_sockptr(optlen, &len, sizeof(int))) {
-			put_unused_fd(pidfd);
-			fput(pidfd_file);
-
-			return -EFAULT;
-		}
+	case SO_PEERPIDFD_THREAD:
+		/* Only AF_UNIX records the peer's connecting thread. */
+		if (!sk_is_unix(sk))
+			return -EOPNOTSUPP;
 
-		fd_install(pidfd, pidfd_file);
-		return 0;
-	}
+		return sk_getsockopt_peerpidfd(sk, PIDTYPE_PID, optval, optlen, len);
 
 	case SO_PEERGROUPS:
 	{
diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index d01ee76c8026..563d9827c5cc 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -1056,6 +1056,7 @@ static bool unix_bpf_bypass_getsockopt(int level, int optname)
 	if (level == SOL_SOCKET) {
 		switch (optname) {
 		case SO_PEERPIDFD:
+		case SO_PEERPIDFD_THREAD:
 			return true;
 		default:
 			return false;

-- 
2.53.0

[PATCH 08/10] selftests/net: SO_PEERPIDFD_THREAD

[Christian Brauner]

Add tests for SO_PEERPIDFD_THREAD.

Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
---
 tools/testing/selftests/net/af_unix/scm_pidfd.c | 97 +++++++++++++++++++++++++
 1 file changed, 97 insertions(+)

diff --git a/tools/testing/selftests/net/af_unix/scm_pidfd.c b/tools/testing/selftests/net/af_unix/scm_pidfd.c
index 019c48e1cdcd..bbbd5e7b4fa7 100644
--- a/tools/testing/selftests/net/af_unix/scm_pidfd.c
+++ b/tools/testing/selftests/net/af_unix/scm_pidfd.c
@@ -32,6 +32,10 @@
 #define SO_PASSPIDFD_THREAD 86
 #endif
 
+#ifndef SO_PEERPIDFD_THREAD
+#define SO_PEERPIDFD_THREAD 87
+#endif
+
 #define CHILD_EXIT_CODE_OK 123
 
 static void child_die()
@@ -822,4 +826,97 @@ TEST(scm_pidfd_thread_creds)
 	EXPECT_EQ(ids.pid, info.tgid);
 }
 
+static void *peer_connect_thread(void *arg)
+{
+	struct sock_addr *sa = arg;
+	struct thread_ids ids = {
+		.pid = getpid(),
+		.tid = gettid(),
+	};
+	int fd;
+	char sync;
+
+	fd = socket(AF_UNIX, SOCK_STREAM, 0);
+	if (fd < 0)
+		return (void *)1;
+
+	if (connect(fd, (struct sockaddr *)&sa->listen_addr, sa->addrlen))
+		return (void *)1;
+
+	if (send(fd, &ids, sizeof(ids), 0) != sizeof(ids))
+		return (void *)1;
+
+	/* stay alive until the server has looked at our pidfd */
+	if (read(fd, &sync, 1) != 1)
+		return (void *)1;
+
+	close(fd);
+	return NULL;
+}
+
+static int peer_pidfd_info(int fd, int optname, struct pidfd_info *info)
+{
+	int pidfd;
+	socklen_t len = sizeof(pidfd);
+
+	if (getsockopt(fd, SOL_SOCKET, optname, &pidfd, &len)) {
+		log_err("getsockopt(SO_PEERPIDFD*)");
+		return -1;
+	}
+
+	info->mask = PIDFD_INFO_PID;
+	if (ioctl(pidfd, PIDFD_GET_INFO, info)) {
+		log_err("ioctl(PIDFD_GET_INFO)");
+		close(pidfd);
+		return -1;
+	}
+
+	close(pidfd);
+	return 0;
+}
+
+/* SO_PEERPIDFD_THREAD returns a pidfd for the peer's connecting thread. */
+TEST(so_peerpidfd_thread)
+{
+	struct sock_addr sa;
+	struct thread_ids ids;
+	struct pidfd_info info;
+	pthread_t thread;
+	void *tret;
+	int server, cfd;
+
+	server = socket(AF_UNIX, SOCK_STREAM, 0);
+	ASSERT_LE(0, server);
+
+	fill_sockaddr(&sa, true);
+	ASSERT_EQ(0, bind(server, (struct sockaddr *)&sa.listen_addr, sa.addrlen));
+	ASSERT_EQ(0, listen(server, 1));
+
+	ASSERT_EQ(0, pthread_create(&thread, NULL, peer_connect_thread, &sa));
+
+	cfd = accept(server, NULL, NULL);
+	ASSERT_LE(0, cfd);
+
+	ASSERT_EQ(sizeof(ids), recv(cfd, &ids, sizeof(ids), MSG_WAITALL));
+	ASSERT_NE(ids.pid, ids.tid);
+
+	/* SO_PEERPIDFD refers to the peer's thread-group. */
+	ASSERT_EQ(0, peer_pidfd_info(cfd, SO_PEERPIDFD, &info));
+	EXPECT_EQ(ids.pid, info.pid);
+	EXPECT_EQ(ids.pid, info.tgid);
+
+	/* SO_PEERPIDFD_THREAD refers to the connecting thread. */
+	ASSERT_EQ(0, peer_pidfd_info(cfd, SO_PEERPIDFD_THREAD, &info));
+	EXPECT_EQ(ids.tid, info.pid);
+	EXPECT_EQ(ids.pid, info.tgid);
+
+	/* release the connecting thread */
+	ASSERT_EQ(1, write(cfd, "x", 1));
+	ASSERT_EQ(0, pthread_join(thread, &tret));
+	ASSERT_EQ(NULL, tret);
+
+	close(cfd);
+	close(server);
+}
+
 TEST_HARNESS_MAIN

-- 
2.53.0

[PATCH 09/10] pidfs: record the coredump on the dumping thread's pid too

[Christian Brauner]

If a thread-group coredumps only the thread-group leader pidfd will
return coredump information. A pidfd for the thread that took the fatal
signal cannot be used to retrieve it.

Record both the thread-group leader and the specific thread that took
the signal and register both in pidfs. Mark both the thread-group leader
and the specific thread with the coredump information so retrieval works
for both pidfds.

Now that both SO_PEERPIDFD and SO_PEERPIDFD_THREAD are available it's
easy to get the coredump information for the specific thread.

Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
---
 fs/coredump.c            | 22 +++++++++++++---------
 fs/pidfs.c               | 11 +++++++++--
 include/linux/coredump.h |  4 +++-
 3 files changed, 25 insertions(+), 12 deletions(-)

diff --git a/fs/coredump.c b/fs/coredump.c
index 71a0093ada1b..b5ff4b3e1831 100644
--- a/fs/coredump.c
+++ b/fs/coredump.c
@@ -454,7 +454,7 @@ static bool coredump_parse(struct core_name *cn, struct coredump_params *cprm,
 				 * leader we know that the thread-group leader
 				 * cannot be reaped until @current has exited.
 				 */
-				cprm->pid = task_tgid(current);
+				task_pids(cprm->pid, current);
 				err = cn_printf(cn, "%d", COREDUMP_PIDFD_NUMBER);
 				break;
 			}
@@ -626,13 +626,17 @@ static int umh_coredump_setup(struct subprocess_info *info, struct cred *new)
 	struct coredump_params *cp = (struct coredump_params *)info->data;
 	int err;
 
-	if (cp->pid) {
+	if (cp->pid[PIDTYPE_TGID]) {
 		struct file *pidfs_file __free(fput) = NULL;
 
-		pidfs_file = pidfs_alloc_file(cp->pid, 0);
+		pidfs_file = pidfs_alloc_file(cp->pid[PIDTYPE_TGID], 0);
 		if (IS_ERR(pidfs_file))
 			return PTR_ERR(pidfs_file);
 
+		err = pidfs_register_pids(cp->pid);
+		if (err)
+			return err;
+
 		pidfs_coredump(cp);
 
 		/*
@@ -695,12 +699,12 @@ static bool coredump_sock_connect(struct core_name *cn, struct coredump_params *
 		return false;
 
 	/*
-	 * Set the thread-group leader pid which is used for the peer
-	 * credentials during connect() below. Then immediately register
-	 * it in pidfs...
+	 * Set the pids of the dumping thread and its thread-group leader
+	 * which are used for the peer credentials during connect() below.
+	 * Then immediately register them in pidfs...
 	 */
-	cprm->pid = task_tgid(current);
-	retval = pidfs_register_pid(cprm->pid);
+	task_pids(cprm->pid, current);
+	retval = pidfs_register_pids(cprm->pid);
 	if (retval)
 		return false;
 
@@ -722,7 +726,7 @@ static bool coredump_sock_connect(struct core_name *cn, struct coredump_params *
 	}
 
 	/* ... and validate that @sk_peer_pid matches @cprm.pid. */
-	if (WARN_ON_ONCE(unix_peer(socket->sk)->sk_peer_pid[PIDTYPE_TGID] != cprm->pid))
+	if (WARN_ON_ONCE(!pids_equal(unix_peer(socket->sk)->sk_peer_pid, cprm->pid)))
 		return false;
 
 	cprm->limit = RLIM_INFINITY;
diff --git a/fs/pidfs.c b/fs/pidfs.c
index 586af2e5811c..29299b2c7ca7 100644
--- a/fs/pidfs.c
+++ b/fs/pidfs.c
@@ -793,9 +793,9 @@ void pidfs_exit(struct task_struct *tsk)
 }
 
 #ifdef CONFIG_COREDUMP
-void pidfs_coredump(const struct coredump_params *cprm)
+static void pidfs_coredump_pid(struct pid *pid,
+			       const struct coredump_params *cprm)
 {
-	struct pid *pid = cprm->pid;
 	struct pidfs_attr *attr;
 
 	attr = READ_ONCE(pid->attr);
@@ -814,6 +814,13 @@ void pidfs_coredump(const struct coredump_params *cprm)
 	smp_wmb();
 	set_bit(PIDFS_ATTR_BIT_COREDUMP, &attr->attr_mask);
 }
+
+void pidfs_coredump(const struct coredump_params *cprm)
+{
+	/* The dumping thread's pidfd reports the coredump as well. */
+	for (enum pid_type type = PIDTYPE_PID; type <= pids_last(cprm->pid); type++)
+		pidfs_coredump_pid(cprm->pid[type], cprm);
+}
 #endif
 
 static struct vfsmount *pidfs_mnt __ro_after_init;
diff --git a/include/linux/coredump.h b/include/linux/coredump.h
index 7b38ee2e7913..0bbb7de6a402 100644
--- a/include/linux/coredump.h
+++ b/include/linux/coredump.h
@@ -5,6 +5,7 @@
 #include <linux/types.h>
 #include <linux/mm.h>
 #include <linux/fs.h>
+#include <linux/pid_types.h>
 #include <linux/sched/coredump.h>
 #include <asm/siginfo.h>
 
@@ -32,7 +33,8 @@ struct coredump_params {
 	int vma_count;
 	size_t vma_data_size;
 	struct core_vma_metadata *vma_meta;
-	struct pid *pid;
+	/* Dumping thread and its thread-group leader by pid type. */
+	DECLARE_PIDS(pid, PIDTYPE_TGID);
 };
 
 extern unsigned int core_file_note_size_limit;

-- 
2.53.0

[PATCH 10/10] selftests/coredump: check the dumping thread's pidfd

[Christian Brauner]

Crash from a non-leader thread and verify that the pidfd from
SO_PEERPIDFD_THREAD on the coredump socket refers to that thread and
reports the coredump like the thread-group leader's pidfd does.

Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
---
 .../selftests/coredump/coredump_socket_test.c      | 175 +++++++++++++++++++++
 tools/testing/selftests/coredump/coredump_test.h   |   2 +
 .../selftests/coredump/coredump_test_helpers.c     |  49 ++++++
 3 files changed, 226 insertions(+)

diff --git a/tools/testing/selftests/coredump/coredump_socket_test.c b/tools/testing/selftests/coredump/coredump_socket_test.c
index 422728f632ca..ec73bb690bbc 100644
--- a/tools/testing/selftests/coredump/coredump_socket_test.c
+++ b/tools/testing/selftests/coredump/coredump_socket_test.c
@@ -592,6 +592,181 @@ TEST_F(coredump, socket_coredump_signal_sigsegv)
 	wait_and_check_coredump_server(pid_coredump_server, _metadata, self);
 }
 
+static bool check_coredump_info(const struct pidfd_info *info, const char *what)
+{
+	if (!(info->mask & PIDFD_INFO_COREDUMP)) {
+		fprintf(stderr, "%s: PIDFD_INFO_COREDUMP not set in mask\n", what);
+		return false;
+	}
+
+	if (!(info->coredump_mask & PIDFD_COREDUMPED)) {
+		fprintf(stderr, "%s: PIDFD_COREDUMPED not set in coredump_mask\n", what);
+		return false;
+	}
+
+	if (!(info->mask & PIDFD_INFO_COREDUMP_SIGNAL) || info->coredump_signal != SIGSEGV) {
+		fprintf(stderr, "%s: coredump_signal=%d, expected SIGSEGV=%d\n",
+			what, info->coredump_signal, SIGSEGV);
+		return false;
+	}
+
+	if (!(info->mask & PIDFD_INFO_COREDUMP_CODE) || info->coredump_code != SEGV_MAPERR) {
+		fprintf(stderr, "%s: coredump_code=%d, expected SEGV_MAPERR=%d\n",
+			what, info->coredump_code, SEGV_MAPERR);
+		return false;
+	}
+
+	return true;
+}
+
+/*
+ * Test: PIDFD_INFO_COREDUMP on the dumping thread's pidfd
+ *
+ * Crash from a non-leader thread and verify that the pidfd from
+ * SO_PEERPIDFD_THREAD refers to that thread and reports the coredump
+ * like the thread-group leader's pidfd from SO_PEERPIDFD does.
+ */
+TEST_F(coredump, socket_coredump_thread)
+{
+	int pidfd, ret, status;
+	pid_t pid, pid_coredump_server;
+	struct pidfd_info info = {};
+	int ipc_sockets[2];
+	char c;
+
+	ASSERT_TRUE(set_core_pattern("@/tmp/coredump.socket"));
+
+	ret = socketpair(AF_UNIX, SOCK_STREAM | SOCK_CLOEXEC, 0, ipc_sockets);
+	ASSERT_EQ(ret, 0);
+
+	pid_coredump_server = fork();
+	ASSERT_GE(pid_coredump_server, 0);
+	if (pid_coredump_server == 0) {
+		int fd_server = -1, fd_coredump = -1, fd_peer_pidfd = -1;
+		int fd_thread_pidfd = -1, fd_core_file = -1;
+		struct pidfd_info thread_info = {};
+		int exit_code = EXIT_FAILURE;
+
+		close(ipc_sockets[0]);
+
+		fd_server = create_and_listen_unix_socket("/tmp/coredump.socket");
+		if (fd_server < 0) {
+			fprintf(stderr, "socket_coredump_thread: listen socket failed: %m\n");
+			goto out;
+		}
+
+		if (write_nointr(ipc_sockets[1], "1", 1) < 0) {
+			fprintf(stderr, "socket_coredump_thread: ipc write failed: %m\n");
+			goto out;
+		}
+
+		close(ipc_sockets[1]);
+
+		fd_coredump = accept4(fd_server, NULL, NULL, SOCK_CLOEXEC);
+		if (fd_coredump < 0) {
+			fprintf(stderr, "socket_coredump_thread: accept4 failed: %m\n");
+			goto out;
+		}
+
+		fd_peer_pidfd = get_peer_pidfd(fd_coredump);
+		if (fd_peer_pidfd < 0) {
+			fprintf(stderr, "socket_coredump_thread: get_peer_pidfd failed\n");
+			goto out;
+		}
+
+		fd_thread_pidfd = get_peer_pidfd_thread(fd_coredump);
+		if (fd_thread_pidfd < 0) {
+			fprintf(stderr, "socket_coredump_thread: get_peer_pidfd_thread failed\n");
+			goto out;
+		}
+
+		if (!get_pidfd_info(fd_peer_pidfd, &info) ||
+		    !get_pidfd_info(fd_thread_pidfd, &thread_info)) {
+			fprintf(stderr, "socket_coredump_thread: get_pidfd_info failed\n");
+			goto out;
+		}
+
+		/* The peer is the thread-group leader, the dumping thread is not. */
+		if (info.pid != info.tgid || thread_info.tgid != info.tgid ||
+		    thread_info.pid == thread_info.tgid) {
+			fprintf(stderr, "socket_coredump_thread: unexpected ids %d/%d and %d/%d\n",
+				info.pid, info.tgid, thread_info.pid, thread_info.tgid);
+			goto out;
+		}
+
+		if (!check_coredump_info(&info, "SO_PEERPIDFD") ||
+		    !check_coredump_info(&thread_info, "SO_PEERPIDFD_THREAD"))
+			goto out;
+
+		fd_core_file = open_coredump_tmpfile(self->fd_tmpfs_detached);
+		if (fd_core_file < 0) {
+			fprintf(stderr, "socket_coredump_thread: core tmpfile failed: %m\n");
+			goto out;
+		}
+
+		for (;;) {
+			char buffer[4096];
+			ssize_t bytes_read, bytes_write;
+
+			bytes_read = read(fd_coredump, buffer, sizeof(buffer));
+			if (bytes_read < 0) {
+				fprintf(stderr, "socket_coredump_thread: core read failed: %m\n");
+				goto out;
+			}
+
+			if (bytes_read == 0)
+				break;
+
+			bytes_write = write(fd_core_file, buffer, bytes_read);
+			if (bytes_read != bytes_write) {
+				fprintf(stderr, "socket_coredump_thread: core write %zd/%zd: %m\n",
+					bytes_read, bytes_write);
+				goto out;
+			}
+		}
+
+		exit_code = EXIT_SUCCESS;
+		fprintf(stderr, "socket_coredump_thread: completed successfully\n");
+out:
+		if (fd_core_file >= 0)
+			close(fd_core_file);
+		if (fd_thread_pidfd >= 0)
+			close(fd_thread_pidfd);
+		if (fd_peer_pidfd >= 0)
+			close(fd_peer_pidfd);
+		if (fd_coredump >= 0)
+			close(fd_coredump);
+		if (fd_server >= 0)
+			close(fd_server);
+		_exit(exit_code);
+	}
+	self->pid_coredump_server = pid_coredump_server;
+
+	EXPECT_EQ(close(ipc_sockets[1]), 0);
+	ASSERT_EQ(read_nointr(ipc_sockets[0], &c, 1), 1);
+	EXPECT_EQ(close(ipc_sockets[0]), 0);
+
+	pid = fork();
+	ASSERT_GE(pid, 0);
+	if (pid == 0)
+		crashing_child_thread();
+
+	pidfd = sys_pidfd_open(pid, 0);
+	ASSERT_GE(pidfd, 0);
+
+	waitpid(pid, &status, 0);
+	ASSERT_TRUE(WIFSIGNALED(status));
+	ASSERT_EQ(WTERMSIG(status), SIGSEGV);
+	ASSERT_TRUE(WCOREDUMP(status));
+
+	ASSERT_TRUE(get_pidfd_info(pidfd, &info));
+	ASSERT_TRUE(!!(info.mask & PIDFD_INFO_COREDUMP));
+	ASSERT_TRUE(!!(info.coredump_mask & PIDFD_COREDUMPED));
+	ASSERT_EQ(info.coredump_signal, SIGSEGV);
+
+	wait_and_check_coredump_server(pid_coredump_server, _metadata, self);
+}
+
 /*
  * Test: PIDFD_INFO_COREDUMP_SIGNAL via simple socket coredump with SIGABRT
  *
diff --git a/tools/testing/selftests/coredump/coredump_test.h b/tools/testing/selftests/coredump/coredump_test.h
index ed47f01fa53c..4212656e31f0 100644
--- a/tools/testing/selftests/coredump/coredump_test.h
+++ b/tools/testing/selftests/coredump/coredump_test.h
@@ -27,10 +27,12 @@ FIXTURE(coredump)
 /* Shared helper function declarations */
 void *do_nothing(void *arg);
 void crashing_child(void);
+void crashing_child_thread(void);
 int create_detached_tmpfs(void);
 int create_and_listen_unix_socket(const char *path);
 bool set_core_pattern(const char *pattern);
 int get_peer_pidfd(int fd);
+int get_peer_pidfd_thread(int fd);
 bool get_pidfd_info(int fd_peer_pidfd, struct pidfd_info *info);
 
 /* Inline helper that uses harness types */
diff --git a/tools/testing/selftests/coredump/coredump_test_helpers.c b/tools/testing/selftests/coredump/coredump_test_helpers.c
index 2a20faf9cb0a..36306069f62e 100644
--- a/tools/testing/selftests/coredump/coredump_test_helpers.c
+++ b/tools/testing/selftests/coredump/coredump_test_helpers.c
@@ -13,6 +13,7 @@
 #include <string.h>
 #include <sys/epoll.h>
 #include <sys/ioctl.h>
+#include <sys/mman.h>
 #include <sys/socket.h>
 #include <sys/types.h>
 #include <sys/un.h>
@@ -38,6 +39,10 @@ struct _fixture_coredump_data {
 
 #define NUM_THREAD_SPAWN 128
 
+#ifndef SO_PEERPIDFD_THREAD
+#define SO_PEERPIDFD_THREAD 87
+#endif
+
 void *do_nothing(void *arg)
 {
 	(void)arg;
@@ -59,6 +64,36 @@ void crashing_child(void)
 	i = *(volatile int *)NULL;
 }
 
+static void *crashing_thread(void *arg)
+{
+	int *p;
+
+	(void)arg;
+
+	/* crash on purpose with SEGV_MAPERR */
+	p = mmap(NULL, PAGE_SIZE, PROT_READ | PROT_WRITE,
+		 MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+	if (p == MAP_FAILED)
+		return NULL;
+	munmap(p, PAGE_SIZE);
+	*p = 0;
+
+	return NULL;
+}
+
+void crashing_child_thread(void)
+{
+	pthread_t thread;
+	int i;
+
+	for (i = 0; i < NUM_THREAD_SPAWN; ++i)
+		pthread_create(&thread, NULL, do_nothing, NULL);
+
+	/* crash from a non-leader thread */
+	pthread_create(&thread, NULL, crashing_thread, NULL);
+	pause();
+}
+
 int create_detached_tmpfs(void)
 {
 	int fd_context, fd_tmpfs;
@@ -138,6 +173,20 @@ int get_peer_pidfd(int fd)
 	return fd_peer_pidfd;
 }
 
+int get_peer_pidfd_thread(int fd)
+{
+	int fd_peer_pidfd;
+	socklen_t fd_peer_pidfd_len = sizeof(fd_peer_pidfd);
+	int ret = getsockopt(fd, SOL_SOCKET, SO_PEERPIDFD_THREAD, &fd_peer_pidfd,
+			     &fd_peer_pidfd_len);
+	if (ret < 0) {
+		fprintf(stderr, "%s: getsockopt(SO_PEERPIDFD_THREAD) failed: %m\n", __func__);
+		return -1;
+	}
+	fprintf(stderr, "%s: successfully retrieved pidfd %d\n", __func__, fd_peer_pidfd);
+	return fd_peer_pidfd;
+}
+
 bool get_pidfd_info(int fd_peer_pidfd, struct pidfd_info *info)
 {
 	int ret;

-- 
2.53.0

Re: [PATCH 05/10] net: turn sk_peer_pid into an array indexed by pid type

[Jakub Kicinski]

On Mon, 31 Aug 2026 13:21:17 +0200 Christian Brauner wrote:
> Currently only the struct pid of the thread-group leader is recorded
> for a socket's peer. To make room for the struct pid of the thread that
> called connect(), listen() or socketpair() turn sk_peer_pid into an
> array indexed by pid type. All users, including bluetooth and the
> coredump socket, keep using the PIDTYPE_TGID slot.
> 
> Nothing fills the PIDTYPE_PID slot yet. No functional changes.

This patch suffers from missing kdoc and general inability to build:

Warning: include/net/sock.h:606 struct member 'PIDTYPE_TGID' not described in 'sock'
Warning: include/net/sock.h:606 Excess struct member 'sk_peer_pid' description in 'sock' (did you mean one of: '#define sk_portpair             __sk_common.skc_portpair', 'sk_peer_cred', 'sk_peer_lock', 'sk_peek_off')


include/trace/events/landlock.h:946:13: error: incompatible pointer types assigning to 'struct pid *' from 'struct pid *const volatile *' [-Wincompatible-pointer-types]


What's the merging path for these? Judging by the To: perhaps you
expect us to take these directly?
-- 
pw-bot: cr

Re: [PATCH 05/10] net: turn sk_peer_pid into an array indexed by pid type

[Christian Brauner]

On 2026-09-01 17:20 -0700, Jakub Kicinski wrote:
> On Mon, 31 Aug 2026 13:21:17 +0200 Christian Brauner wrote:
> > Currently only the struct pid of the thread-group leader is recorded
> > for a socket's peer. To make room for the struct pid of the thread that
> > called connect(), listen() or socketpair() turn sk_peer_pid into an
> > array indexed by pid type. All users, including bluetooth and the
> > coredump socket, keep using the PIDTYPE_TGID slot.
> > 
> > Nothing fills the PIDTYPE_PID slot yet. No functional changes.
> 
> This patch suffers from missing kdoc and general inability to build:

Oh, damn, the automated pipeline should have done a per-patch build.
Fixing, thanks!

> Warning: include/net/sock.h:606 struct member 'PIDTYPE_TGID' not described in 'sock'
> Warning: include/net/sock.h:606 Excess struct member 'sk_peer_pid' description in 'sock' (did you mean one of: '#define sk_portpair             __sk_common.skc_portpair', 'sk_peer_cred', 'sk_peer_lock', 'sk_peek_off')
> 
> 
> include/trace/events/landlock.h:946:13: error: incompatible pointer types assigning to 'struct pid *' from 'struct pid *const volatile *' [-Wincompatible-pointer-types]
> 
> 
> What's the merging path for these? Judging by the To: perhaps you
> expect us to take these directly?

If you have no quarrels with me taking it through the vfs tree it would
help because I have other work on top of this. Otherwise a shared branch
also works.

Re: [PATCH 05/10] net: turn sk_peer_pid into an array indexed by pid type

[Jakub Kicinski]

On Fri, 04 Sep 2026 11:03:24 +0200 Christian Brauner wrote:
> > Warning: include/net/sock.h:606 struct member 'PIDTYPE_TGID' not described in 'sock'
> > Warning: include/net/sock.h:606 Excess struct member 'sk_peer_pid' description in 'sock' (did you mean one of: '#define sk_portpair             __sk_common.skc_portpair', 'sk_peer_cred', 'sk_peer_lock', 'sk_peek_off')
> > 
> > 
> > include/trace/events/landlock.h:946:13: error: incompatible pointer types assigning to 'struct pid *' from 'struct pid *const volatile *' [-Wincompatible-pointer-types]
> > 
> > 
> > What's the merging path for these? Judging by the To: perhaps you
> > expect us to take these directly?  
> 
> If you have no quarrels with me taking it through the vfs tree it would
> help because I have other work on top of this. Otherwise a shared branch
> also works.

Shared branch, please. It's too much code to be sitting in another tree
for the full development cycle

Re: [PATCH 02/10] af_unix: record the pid of the sending thread

[Alexander Mikhalitsyn]

Am Mo., 31. Aug. 2026 um 13:21 Uhr schrieb Christian Brauner
<brauner@kernel.org>:
>
> Currently only the struct pid of the thread-group leader is recorded.
> The identity of the actual thread that sent the message or is connected
> to a given socket cannot be retrieved.
>
> Add the plumbing to make it possible to retrieve a pidfd for the sender.
> Nothing uses the thread-specific struct pid yet. No functional changes.
>
> Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
> ---
>  include/net/scm.h  |  7 +++----
>  net/core/scm.c     | 21 +++++++++++++++++----
>  net/unix/af_unix.c | 23 +++++++++++++----------
>  net/unix/af_unix.h |  3 ++-
>  4 files changed, 35 insertions(+), 19 deletions(-)
>
> diff --git a/include/net/scm.h b/include/net/scm.h
> index 86ae6bc109ec..aa7d15c5fc27 100644
> --- a/include/net/scm.h
> +++ b/include/net/scm.h
> @@ -42,7 +42,7 @@ struct scm_fp_list {
>  };
>
>  struct scm_cookie {
> -       struct pid              *pid;           /* Skb credentials */
> +       DECLARE_PIDS(pid, PIDTYPE_TGID);        /* Skb credentials by pid type */
>         struct scm_fp_list      *fp;            /* Passed files         */
>         struct scm_creds        creds;          /* Skb credentials      */
>  #ifdef CONFIG_SECURITY_NETWORK
> @@ -69,7 +69,7 @@ static __inline__ void unix_get_peersec_dgram(struct socket *sock, struct scm_co
>  static __inline__ void scm_set_cred(struct scm_cookie *scm,
>                                     struct pid *pid, kuid_t uid, kgid_t gid)
>  {
> -       scm->pid = get_pid(pid);
> +       scm->pid[PIDTYPE_TGID] = get_pid(pid);
>         scm->creds.pid = pid_vnr(pid);
>         scm->creds.uid = uid;
>         scm->creds.gid = gid;
> @@ -77,8 +77,7 @@ static __inline__ void scm_set_cred(struct scm_cookie *scm,
>
>  static __inline__ void scm_destroy_cred(struct scm_cookie *scm)
>  {
> -       put_pid(scm->pid);
> -       scm->pid = NULL;
> +       put_pids(scm->pid);
>  }
>
>  static __inline__ void scm_destroy(struct scm_cookie *scm)
> diff --git a/net/core/scm.c b/net/core/scm.c
> index f0d44ecdb11f..9b9e119c353a 100644
> --- a/net/core/scm.c
> +++ b/net/core/scm.c
> @@ -149,6 +149,7 @@ EXPORT_SYMBOL(__scm_destroy);
>
>  static inline int scm_replace_pid(struct scm_cookie *scm, struct pid *pid)
>  {
> +       struct pid *thread_pid;
>         int err;
>
>         /* drop all previous references */
> @@ -158,7 +159,18 @@ static inline int scm_replace_pid(struct scm_cookie *scm, struct pid *pid)
>         if (unlikely(err))
>                 return err;
>
> -       scm->pid = pid;
> +       /* A sender naming its own thread-group sends from the current thread. */
> +       if (pid == task_tgid(current))
> +               thread_pid = task_pid(current);
> +       else
> +               thread_pid = pid;

Hi Christian,

The patch looks good to me, but this spot raised some doubts for me.

If scm_replace_pid() is called with pid == task_tgid(current) then all
good, because we
get scm->pid[PIDTYPE_TGID] == pid and  scm->pid[PIDTYPE_PID] ==
task_pid(current). All good.

If scm_replace_pid() is supplied with pid that has a type PIDTYPE_TGID, then:
- scm->pid[PIDTYPE_TGID] == pid. Good.
- scm->pid[PIDTYPE_PID] = pid. Doesn't looks correct, shoudn't we do
something like:
{
        struct task_struct *task;

        rcu_read_lock();
        task = pid_task(pid, PIDTYPE_TGID);
        thread_pid = task_pid(task);
        rcu_read_unlock();
}

to get a correct thread_pid for both cases here?

Kind regards,
Alex

> +
> +       err = pidfs_register_pid(thread_pid);
> +       if (unlikely(err))
> +               return err;
> +
> +       scm->pid[PIDTYPE_TGID] = pid;
> +       scm->pid[PIDTYPE_PID] = get_pid(thread_pid);
>         scm->creds.pid = pid_vnr(pid);
>         return 0;
>  }
> @@ -207,7 +219,8 @@ int __scm_send(struct socket *sock, struct msghdr *msg, struct scm_cookie *p)
>                         if (err)
>                                 goto error;
>
> -                       if (!p->pid || pid_vnr(p->pid) != creds.pid) {
> +                       if (!p->pid[PIDTYPE_TGID] ||
> +                           pid_vnr(p->pid[PIDTYPE_TGID]) != creds.pid) {
>                                 struct pid *pid;
>                                 err = -ESRCH;
>                                 pid = find_get_pid(creds.pid);
> @@ -504,10 +517,10 @@ static void scm_pidfd_recv(struct msghdr *msg, struct scm_cookie *scm)
>                 return;
>         }
>
> -       if (!scm->pid)
> +       if (!scm->pid[PIDTYPE_TGID])
>                 return;
>
> -       pidfd = pidfd_prepare(scm->pid, PIDFD_STALE, &pidfd_file);
> +       pidfd = pidfd_prepare(scm->pid[PIDTYPE_TGID], PIDFD_STALE, &pidfd_file);
>
>         if (put_cmsg(msg, SOL_SOCKET, SCM_PIDFD, sizeof(int), &pidfd)) {
>                 if (pidfd_file) {
> diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
> index 13f9926bf205..011af84e3626 100644
> --- a/net/unix/af_unix.c
> +++ b/net/unix/af_unix.c
> @@ -1973,7 +1973,7 @@ static void unix_destruct_scm(struct sk_buff *skb)
>  {
>         struct scm_cookie scm = {};
>
> -       swap(scm.pid, UNIXCB(skb).pid);
> +       swap_pids(scm.pid, UNIXCB(skb).pid);
>
>         if (UNIXCB(skb).fp)
>                 unix_detach_fds(&scm, skb);
> @@ -1991,7 +1991,7 @@ static int unix_scm_to_skb(struct scm_cookie *scm, struct sk_buff *skb, bool sen
>  {
>         int err = 0;
>
> -       UNIXCB(skb).pid = get_pid(scm->pid);
> +       get_pids(UNIXCB(skb).pid, scm->pid);
>         UNIXCB(skb).uid = scm->creds.uid;
>         UNIXCB(skb).gid = scm->creds.gid;
>         UNIXCB(skb).fp = NULL;
> @@ -2005,7 +2005,10 @@ static int unix_scm_to_skb(struct scm_cookie *scm, struct sk_buff *skb, bool sen
>
>  static void unix_skb_to_scm(struct sk_buff *skb, struct scm_cookie *scm)
>  {
> -       scm_set_cred(scm, UNIXCB(skb).pid, UNIXCB(skb).uid, UNIXCB(skb).gid);
> +       get_pids(scm->pid, UNIXCB(skb).pid);
> +       scm->creds.pid = pid_vnr(scm->pid[PIDTYPE_TGID]);
> +       scm->creds.uid = UNIXCB(skb).uid;
> +       scm->creds.gid = UNIXCB(skb).gid;
>         unix_set_secdata(scm, skb);
>  }
>
> @@ -2025,20 +2028,20 @@ static void unix_skb_to_scm(struct sk_buff *skb, struct scm_cookie *scm)
>  static int unix_maybe_add_creds(struct sk_buff *skb, const struct sock *sk,
>                                 const struct sock *other)
>  {
> -       if (UNIXCB(skb).pid)
> +       if (UNIXCB(skb).pid[PIDTYPE_TGID])
>                 return 0;
>
>         if (unix_may_passcred(sk) || unix_may_passcred(other) ||
>             !other->sk_socket) {
> -               struct pid *pid;
>                 int err;
>
> -               pid = task_tgid(current);
> -               err = pidfs_register_pid(pid);
> -               if (unlikely(err))
> +               get_task_pids(UNIXCB(skb).pid, current);
> +               err = pidfs_register_pids(UNIXCB(skb).pid);
> +               if (unlikely(err)) {
> +                       put_pids(UNIXCB(skb).pid);
>                         return err;
> +               }
>
> -               UNIXCB(skb).pid = get_pid(pid);
>                 current_uid_gid(&UNIXCB(skb).uid, &UNIXCB(skb).gid);
>         }
>
> @@ -2048,7 +2051,7 @@ static int unix_maybe_add_creds(struct sk_buff *skb, const struct sock *sk,
>  static bool unix_skb_scm_eq(struct sk_buff *skb,
>                             struct scm_cookie *scm)
>  {
> -       return UNIXCB(skb).pid == scm->pid &&
> +       return UNIXCB(skb).pid[PIDTYPE_TGID] == scm->pid[PIDTYPE_TGID] &&
>                uid_eq(UNIXCB(skb).uid, scm->creds.uid) &&
>                gid_eq(UNIXCB(skb).gid, scm->creds.gid) &&
>                unix_secdata_eq(scm, skb);
> diff --git a/net/unix/af_unix.h b/net/unix/af_unix.h
> index 8119dbeef3a3..402742895acc 100644
> --- a/net/unix/af_unix.h
> +++ b/net/unix/af_unix.h
> @@ -2,6 +2,7 @@
>  #ifndef __AF_UNIX_H
>  #define __AF_UNIX_H
>
> +#include <linux/pid_types.h>
>  #include <linux/uidgid.h>
>
>  #define UNIX_HASH_MOD  (256 - 1)
> @@ -11,7 +12,7 @@
>  struct sock *unix_peer_get(struct sock *sk);
>
>  struct unix_skb_parms {
> -       struct pid              *pid;           /* skb credentials      */
> +       DECLARE_PIDS(pid, PIDTYPE_TGID);        /* skb credentials by pid type */
>         kuid_t                  uid;
>         kgid_t                  gid;
>         struct scm_fp_list      *fp;            /* Passed files         */
>
> --
> 2.53.0
>

Re: [PATCH 03/10] net: add SO_PASSPIDFD_THREAD to get a thread-specific SCM_PIDFD

[Alexander Mikhalitsyn]

Am Mo., 31. Aug. 2026 um 13:21 Uhr schrieb Christian Brauner
<brauner@kernel.org>:
>
> Currently, SCM_PIDFD carries a pidfd for the thread-group leader. A
> broker or the coredump server cannot learn the identity of the specific
> thread that sent a given message. Now that both struct pids are recorded
> a receiver can ask for the specific identity it needs.
>
> So add SO_PASSPIDFD_THREAD as a sibling of SO_PASSPIDFD. Either option
> makes recvmsg() deliver an SCM_PIDFD. SO_PASSPIDFD sends a pidfd for the
> thread-group leader and SO_PASSPIDFD_THREAD sends a pidfd for the
> specific thread.
>
> The two options are mutually exclusive. Enabling one switches the other
> off, so getsockopt() always reports which of the two is active.
>
> On SOCK_STREAM sockets recvmsg() only stops merging data at a thread
> boundary when the receiver asked for a thread pidfd. For SO_PASSCRED and
> SO_PASSPIDFD receivers all threads of one process remain a single
> writer.
>
> Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>

LGTM

Reviewed-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@futurfusion.io>

> ---
>  arch/alpha/include/uapi/asm/socket.h  |  2 ++
>  arch/mips/include/uapi/asm/socket.h   |  2 ++
>  arch/parisc/include/uapi/asm/socket.h |  2 ++
>  arch/sparc/include/uapi/asm/socket.h  |  2 ++
>  include/net/sock.h                    | 10 +++++++++-
>  include/uapi/asm-generic/socket.h     |  2 ++
>  net/core/scm.c                        | 19 +++++++++++++------
>  net/core/sock.c                       | 26 ++++++++++++++++++++++++--
>  net/unix/af_unix.c                    | 11 ++++++++---
>  9 files changed, 64 insertions(+), 12 deletions(-)
>
> diff --git a/arch/alpha/include/uapi/asm/socket.h b/arch/alpha/include/uapi/asm/socket.h
> index 946a5fad2691..bb3d534826bb 100644
> --- a/arch/alpha/include/uapi/asm/socket.h
> +++ b/arch/alpha/include/uapi/asm/socket.h
> @@ -157,6 +157,8 @@
>
>  #define SO_RIGHTS_NOTRUNC      85
>
> +#define SO_PASSPIDFD_THREAD    86
> +
>  #if !defined(__KERNEL__)
>
>  #if __BITS_PER_LONG == 64
> diff --git a/arch/mips/include/uapi/asm/socket.h b/arch/mips/include/uapi/asm/socket.h
> index f1641dde135f..269badcaa086 100644
> --- a/arch/mips/include/uapi/asm/socket.h
> +++ b/arch/mips/include/uapi/asm/socket.h
> @@ -168,6 +168,8 @@
>
>  #define SO_RIGHTS_NOTRUNC      85
>
> +#define SO_PASSPIDFD_THREAD    86
> +
>  #if !defined(__KERNEL__)
>
>  #if __BITS_PER_LONG == 64
> diff --git a/arch/parisc/include/uapi/asm/socket.h b/arch/parisc/include/uapi/asm/socket.h
> index f3a3815c7dc2..313aee10a52c 100644
> --- a/arch/parisc/include/uapi/asm/socket.h
> +++ b/arch/parisc/include/uapi/asm/socket.h
> @@ -149,6 +149,8 @@
>
>  #define SO_RIGHTS_NOTRUNC      0x4053
>
> +#define SO_PASSPIDFD_THREAD    0x4054
> +
>  #if !defined(__KERNEL__)
>
>  #if __BITS_PER_LONG == 64
> diff --git a/arch/sparc/include/uapi/asm/socket.h b/arch/sparc/include/uapi/asm/socket.h
> index 7907f3b1f0ee..bd3e69bcce7a 100644
> --- a/arch/sparc/include/uapi/asm/socket.h
> +++ b/arch/sparc/include/uapi/asm/socket.h
> @@ -150,6 +150,8 @@
>
>  #define SO_RIGHTS_NOTRUNC        0x005e
>
> +#define SO_PASSPIDFD_THREAD      0x005f
> +
>  #if !defined(__KERNEL__)
>
>
> diff --git a/include/net/sock.h b/include/net/sock.h
> index 51185222aac2..fc09c92e8a83 100644
> --- a/include/net/sock.h
> +++ b/include/net/sock.h
> @@ -356,6 +356,7 @@ struct sk_filter;
>    *    @sk_scm_security: flagged by SO_PASSSEC to recv SCM_SECURITY
>    *    @sk_scm_pidfd: flagged by SO_PASSPIDFD to recv SCM_PIDFD
>    *    @sk_scm_rights: flagged by SO_PASSRIGHTS to recv SCM_RIGHTS
> +  *    @sk_scm_pidfd_thread: flagged by SO_PASSPIDFD_THREAD to recv a thread SCM_PIDFD
>    *    @sk_scm_unused: unused flags for scm_recv()
>    *    @ns_tracker: tracker for netns reference
>    *    @sk_user_frags: xarray of pages the user is holding a reference on.
> @@ -562,7 +563,8 @@ struct sock {
>                                 sk_scm_security : 1,
>                                 sk_scm_pidfd : 1,
>                                 sk_scm_rights : 1,
> -                               sk_scm_unused : 4;
> +                               sk_scm_pidfd_thread : 1,
> +                               sk_scm_unused : 3;
>                 };
>         };
>         u8                      sk_clockid;
> @@ -2986,6 +2988,12 @@ static inline bool sk_is_stream_unix(const struct sock *sk)
>         return sk_is_unix(sk) && sk->sk_type == SOCK_STREAM;
>  }
>
> +/* SO_PASSPIDFD or SO_PASSPIDFD_THREAD asked for an SCM_PIDFD. */
> +static inline bool sk_scm_pidfd_wanted(const struct sock *sk)
> +{
> +       return sk->sk_scm_pidfd || sk->sk_scm_pidfd_thread;
> +}
> +
>  static inline bool sk_is_vsock(const struct sock *sk)
>  {
>         return sk->sk_family == AF_VSOCK;
> diff --git a/include/uapi/asm-generic/socket.h b/include/uapi/asm-generic/socket.h
> index 84ea7b92936e..d1e5c6de146d 100644
> --- a/include/uapi/asm-generic/socket.h
> +++ b/include/uapi/asm-generic/socket.h
> @@ -152,6 +152,8 @@
>
>  #define SO_RIGHTS_NOTRUNC      85
>
> +#define SO_PASSPIDFD_THREAD    86
> +
>  #if !defined(__KERNEL__)
>
>  #if __BITS_PER_LONG == 64 || (defined(__x86_64__) && defined(__ILP32__))
> diff --git a/net/core/scm.c b/net/core/scm.c
> index 9b9e119c353a..d69768414af4 100644
> --- a/net/core/scm.c
> +++ b/net/core/scm.c
> @@ -499,9 +499,13 @@ static bool scm_has_secdata(struct sock *sk)
>  }
>  #endif
>
> -static void scm_pidfd_recv(struct msghdr *msg, struct scm_cookie *scm)
> +static void scm_pidfd_recv(struct sock *sk, struct msghdr *msg,
> +                          struct scm_cookie *scm)
>  {
> +       enum pid_type type = sk->sk_scm_pidfd_thread ? PIDTYPE_PID : PIDTYPE_TGID;
> +       struct pid *pid = scm->pid[type];
>         struct file *pidfd_file = NULL;
> +       unsigned int flags = PIDFD_STALE;
>         int len, pidfd;
>
>         /* put_cmsg() doesn't return an error if CMSG is truncated,
> @@ -517,10 +521,13 @@ static void scm_pidfd_recv(struct msghdr *msg, struct scm_cookie *scm)
>                 return;
>         }
>
> -       if (!scm->pid[PIDTYPE_TGID])
> +       if (!pid)
>                 return;
>
> -       pidfd = pidfd_prepare(scm->pid[PIDTYPE_TGID], PIDFD_STALE, &pidfd_file);
> +       if (type == PIDTYPE_PID)
> +               flags |= PIDFD_THREAD;
> +
> +       pidfd = pidfd_prepare(pid, flags, &pidfd_file);
>
>         if (put_cmsg(msg, SOL_SOCKET, SCM_PIDFD, sizeof(int), &pidfd)) {
>                 if (pidfd_file) {
> @@ -539,7 +546,7 @@ static bool __scm_recv_common(struct sock *sk, struct msghdr *msg,
>                               struct scm_cookie *scm, int flags)
>  {
>         if (!msg->msg_control) {
> -               if (sk->sk_scm_credentials || sk->sk_scm_pidfd ||
> +               if (sk->sk_scm_credentials || sk_scm_pidfd_wanted(sk) ||
>                     scm->fp || scm_has_secdata(sk))
>                         msg->msg_flags |= MSG_CTRUNC;
>
> @@ -586,8 +593,8 @@ void scm_recv_unix(struct socket *sock, struct msghdr *msg,
>                 scm_detach_fds(msg, scm, READ_ONCE(u->scm_rights_notrunc));
>         }
>
> -       if (sock->sk->sk_scm_pidfd)
> -               scm_pidfd_recv(msg, scm);
> +       if (sk_scm_pidfd_wanted(sock->sk))
> +               scm_pidfd_recv(sock->sk, msg, scm);
>
>         scm_destroy_cred(scm);
>  }
> diff --git a/net/core/sock.c b/net/core/sock.c
> index 1ad41904db25..f9615b0de10e 100644
> --- a/net/core/sock.c
> +++ b/net/core/sock.c
> @@ -1571,10 +1571,25 @@ int sk_setsockopt(struct sock *sk, int level, int optname,
>                 break;
>
>         case SO_PASSPIDFD:
> -               if (sk_is_unix(sk))
> +               if (sk_is_unix(sk)) {
> +                       /* Mutually exclusive with SO_PASSPIDFD_THREAD. */
>                         sk->sk_scm_pidfd = valbool;
> -               else
> +                       if (valbool)
> +                               sk->sk_scm_pidfd_thread = 0;
> +               } else {
> +                       ret = -EOPNOTSUPP;
> +               }
> +               break;
> +
> +       case SO_PASSPIDFD_THREAD:
> +               if (sk_is_unix(sk)) {
> +                       /* Mutually exclusive with SO_PASSPIDFD. */
> +                       sk->sk_scm_pidfd_thread = valbool;
> +                       if (valbool)
> +                               sk->sk_scm_pidfd = 0;
> +               } else {
>                         ret = -EOPNOTSUPP;
> +               }
>                 break;
>
>         case SO_PASSRIGHTS:
> @@ -1892,6 +1907,13 @@ int sk_getsockopt(struct sock *sk, int level, int optname,
>                 v.val = sk->sk_scm_pidfd;
>                 break;
>
> +       case SO_PASSPIDFD_THREAD:
> +               if (!sk_is_unix(sk))
> +                       return -EOPNOTSUPP;
> +
> +               v.val = sk->sk_scm_pidfd_thread;
> +               break;
> +
>         case SO_PASSRIGHTS:
>                 if (!sk_is_unix(sk))
>                         return -EOPNOTSUPP;
> diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
> index 011af84e3626..468a9c479b87 100644
> --- a/net/unix/af_unix.c
> +++ b/net/unix/af_unix.c
> @@ -803,7 +803,7 @@ static void copy_peercred(struct sock *sk, struct sock *peersk)
>
>  static bool unix_may_passcred(const struct sock *sk)
>  {
> -       return sk->sk_scm_credentials || sk->sk_scm_pidfd;
> +       return sk->sk_scm_credentials || sk_scm_pidfd_wanted(sk);
>  }
>
>  static int unix_listen(struct socket *sock, int backlog)
> @@ -2048,9 +2048,14 @@ static int unix_maybe_add_creds(struct sk_buff *skb, const struct sock *sk,
>         return 0;
>  }
>
> -static bool unix_skb_scm_eq(struct sk_buff *skb,
> +static bool unix_skb_scm_eq(const struct sock *sk, struct sk_buff *skb,
>                             struct scm_cookie *scm)
>  {
> +       /* Only a thread pidfd receiver can tell threads of one process apart. */
> +       if (sk->sk_scm_pidfd_thread &&
> +           UNIXCB(skb).pid[PIDTYPE_PID] != scm->pid[PIDTYPE_PID])
> +               return false;
> +
>         return UNIXCB(skb).pid[PIDTYPE_TGID] == scm->pid[PIDTYPE_TGID] &&
>                uid_eq(UNIXCB(skb).uid, scm->creds.uid) &&
>                gid_eq(UNIXCB(skb).gid, scm->creds.gid) &&
> @@ -3029,7 +3034,7 @@ static int unix_stream_read_generic(struct unix_stream_read_state *state,
>
>                 if (check_creds) {
>                         /* Never glue messages from different writers */
> -                       if (!unix_skb_scm_eq(skb, &scm))
> +                       if (!unix_skb_scm_eq(sk, skb, &scm))
>                                 break;
>                 } else if (unix_may_passcred(sk)) {
>                         /* Copy credentials */
>
> --
> 2.53.0
>

Re: [PATCH 04/10] selftests/net: SO_PASSPIDFD_THREAD

[Alexander Mikhalitsyn]

Am Mo., 31. Aug. 2026 um 13:21 Uhr schrieb Christian Brauner
<brauner@kernel.org>:
>
> Extend the af_unix scm_pidfd selftest with SO_PASSPIDFD_THREAD tests.
>
> Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>

LGTM

Reviewed-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@futurfusion.io>

> ---
>  tools/testing/selftests/net/af_unix/Makefile    |   2 +
>  tools/testing/selftests/net/af_unix/scm_pidfd.c | 269 ++++++++++++++++++++++++
>  2 files changed, 271 insertions(+)
>
> diff --git a/tools/testing/selftests/net/af_unix/Makefile b/tools/testing/selftests/net/af_unix/Makefile
> index a66f10fb0c23..45b841758f1b 100644
> --- a/tools/testing/selftests/net/af_unix/Makefile
> +++ b/tools/testing/selftests/net/af_unix/Makefile
> @@ -23,6 +23,8 @@ TEST_GEN_FILES := scm_rights_denial_lsm.bpf.o
>  include ../../lib.mk
>  include ../bpf.mk
>
> +$(OUTPUT)/scm_pidfd: CFLAGS += -pthread
> +
>  $(OUTPUT)/scm_rights_denial_lsm: $(BPFOBJ)
>  $(OUTPUT)/scm_rights_denial_lsm: CFLAGS += -I$(SCRATCH_DIR)/include
>  $(OUTPUT)/scm_rights_denial_lsm: LDLIBS += -lelf -lz
> diff --git a/tools/testing/selftests/net/af_unix/scm_pidfd.c b/tools/testing/selftests/net/af_unix/scm_pidfd.c
> index 2c18b92a2603..019c48e1cdcd 100644
> --- a/tools/testing/selftests/net/af_unix/scm_pidfd.c
> +++ b/tools/testing/selftests/net/af_unix/scm_pidfd.c
> @@ -10,6 +10,7 @@
>  #include <unistd.h>
>  #include <string.h>
>  #include <errno.h>
> +#include <pthread.h>
>  #include <sys/un.h>
>  #include <sys/signal.h>
>  #include <sys/types.h>
> @@ -27,6 +28,10 @@
>  #define SCM_PIDFD 0x04
>  #endif
>
> +#ifndef SO_PASSPIDFD_THREAD
> +#define SO_PASSPIDFD_THREAD 86
> +#endif
> +
>  #define CHILD_EXIT_CODE_OK 123
>
>  static void child_die()
> @@ -553,4 +558,268 @@ TEST_F(scm_pidfd, test)
>         close(pfd);
>  }
>
> +struct thread_ids {
> +       pid_t pid;
> +       pid_t tid;
> +};
> +
> +static void *send_ids_thread(void *arg)
> +{
> +       int fd = *(int *)arg;
> +       struct thread_ids ids = {
> +               .pid = getpid(),
> +               .tid = gettid(),
> +       };
> +       char sync;
> +
> +       if (send(fd, &ids, sizeof(ids), 0) != sizeof(ids))
> +               return (void *)1;
> +
> +       /* stay alive until the receiver has looked at our pidfd */
> +       if (read(fd, &sync, 1) != 1)
> +               return (void *)1;
> +
> +       return NULL;
> +}
> +
> +static void *send_ids_creds_thread(void *arg)
> +{
> +       int fd = *(int *)arg;
> +       struct thread_ids ids = {
> +               .pid = getpid(),
> +               .tid = gettid(),
> +       };
> +       struct ucred ucred = {
> +               .pid = getpid(),
> +               .uid = getuid(),
> +               .gid = getgid(),
> +       };
> +       char control[CMSG_SPACE(sizeof(ucred))] = { 0 };
> +       struct iovec iov;
> +       struct msghdr msg = { 0 };
> +       struct cmsghdr *cmsg;
> +       char sync;
> +
> +       iov.iov_base = &ids;
> +       iov.iov_len = sizeof(ids);
> +
> +       msg.msg_iov = &iov;
> +       msg.msg_iovlen = 1;
> +       msg.msg_control = control;
> +       msg.msg_controllen = sizeof(control);
> +
> +       cmsg = CMSG_FIRSTHDR(&msg);
> +       cmsg->cmsg_level = SOL_SOCKET;
> +       cmsg->cmsg_type = SCM_CREDENTIALS;
> +       cmsg->cmsg_len = CMSG_LEN(sizeof(ucred));
> +       memcpy(CMSG_DATA(cmsg), &ucred, sizeof(ucred));
> +
> +       if (sendmsg(fd, &msg, 0) != sizeof(ids))
> +               return (void *)1;
> +
> +       if (read(fd, &sync, 1) != 1)
> +               return (void *)1;
> +
> +       return NULL;
> +}
> +
> +static void thread_client(int fd, int syncfd, void *(*sender)(void *))
> +{
> +       pthread_t thread;
> +       void *ret;
> +       char sync;
> +
> +       /* wait until the receiver enabled SO_PASSPIDFD */
> +       if (read(syncfd, &sync, 1) != 1)
> +               child_die();
> +
> +       if (pthread_create(&thread, NULL, sender, &fd))
> +               child_die();
> +
> +       if (pthread_join(thread, &ret) || ret)
> +               child_die();
> +
> +       exit(0);
> +}
> +
> +static int recv_pidfd(int fd, struct thread_ids *ids)
> +{
> +       char control[CMSG_SPACE(sizeof(int))] = { 0 };
> +       struct iovec iov;
> +       struct msghdr msg = { 0 };
> +       struct cmsghdr *cmsg;
> +       int pidfd = -1;
> +
> +       iov.iov_base = ids;
> +       iov.iov_len = sizeof(*ids);
> +
> +       msg.msg_iov = &iov;
> +       msg.msg_iovlen = 1;
> +       msg.msg_control = control;
> +       msg.msg_controllen = sizeof(control);
> +
> +       if (recvmsg(fd, &msg, 0) != sizeof(*ids)) {
> +               log_err("recvmsg");
> +               return -1;
> +       }
> +
> +       if (msg.msg_flags & (MSG_TRUNC | MSG_CTRUNC)) {
> +               log_err("recvmsg: truncated");
> +               return -1;
> +       }
> +
> +       for (cmsg = CMSG_FIRSTHDR(&msg); cmsg != NULL;
> +            cmsg = CMSG_NXTHDR(&msg, cmsg)) {
> +               if (cmsg->cmsg_level == SOL_SOCKET &&
> +                   cmsg->cmsg_type == SCM_PIDFD)
> +                       memcpy(&pidfd, CMSG_DATA(cmsg), sizeof(pidfd));
> +       }
> +
> +       return pidfd;
> +}
> +
> +static int thread_pidfd_flow(void *(*sender)(void *), int optname,
> +                            struct thread_ids *ids, struct pidfd_info *info)
> +{
> +       int sk[2];
> +       int syncpipe[2];
> +       int pidfd;
> +       int child_status = 0;
> +       pid_t child;
> +
> +       if (socketpair(AF_UNIX, SOCK_STREAM, 0, sk))
> +               return -1;
> +
> +       if (pipe(syncpipe))
> +               return -1;
> +
> +       child = fork();
> +       if (child < 0)
> +               return -1;
> +
> +       if (child == 0) {
> +               close(sk[0]);
> +               close(syncpipe[1]);
> +               thread_client(sk[1], syncpipe[0], sender);
> +       }
> +       close(sk[1]);
> +       close(syncpipe[0]);
> +
> +       int on = 1;
> +
> +       if (setsockopt(sk[0], SOL_SOCKET, optname, &on, sizeof(on))) {
> +               log_err("Failed to set pidfd passing option");
> +               return -1;
> +       }
> +
> +       if (write(syncpipe[1], "1", 1) != 1)
> +               return -1;
> +       close(syncpipe[1]);
> +
> +       pidfd = recv_pidfd(sk[0], ids);
> +       if (pidfd < 0)
> +               return -1;
> +
> +       info->mask = PIDFD_INFO_PID;
> +       if (ioctl(pidfd, PIDFD_GET_INFO, info)) {
> +               log_err("ioctl(PIDFD_GET_INFO)");
> +               close(pidfd);
> +               return -1;
> +       }
> +       close(pidfd);
> +
> +       /* release the sending thread */
> +       if (write(sk[0], "x", 1) != 1)
> +               return -1;
> +       close(sk[0]);
> +
> +       waitpid(child, &child_status, 0);
> +       if (!WIFEXITED(child_status) || WEXITSTATUS(child_status))
> +               return -1;
> +
> +       return 0;
> +}
> +
> +static int sockopt_set(int fd, int optname, int val)
> +{
> +       return setsockopt(fd, SOL_SOCKET, optname, &val, sizeof(val));
> +}
> +
> +static int sockopt_get(int fd, int optname)
> +{
> +       socklen_t len = sizeof(int);
> +       int val = -1;
> +
> +       if (getsockopt(fd, SOL_SOCKET, optname, &val, &len))
> +               return -1;
> +
> +       return val;
> +}
> +
> +TEST(scm_pidfd_setsockopt_values)
> +{
> +       int sk[2];
> +
> +       ASSERT_EQ(0, socketpair(AF_UNIX, SOCK_STREAM, 0, sk));
> +
> +       ASSERT_EQ(0, sockopt_set(sk[0], SO_PASSPIDFD_THREAD, 1));
> +       ASSERT_EQ(1, sockopt_get(sk[0], SO_PASSPIDFD_THREAD));
> +       ASSERT_EQ(0, sockopt_get(sk[0], SO_PASSPIDFD));
> +
> +       /* The option set last wins. */
> +       ASSERT_EQ(0, sockopt_set(sk[0], SO_PASSPIDFD, 1));
> +       ASSERT_EQ(1, sockopt_get(sk[0], SO_PASSPIDFD));
> +       ASSERT_EQ(0, sockopt_get(sk[0], SO_PASSPIDFD_THREAD));
> +
> +       ASSERT_EQ(0, sockopt_set(sk[0], SO_PASSPIDFD_THREAD, 1));
> +       ASSERT_EQ(1, sockopt_get(sk[0], SO_PASSPIDFD_THREAD));
> +       ASSERT_EQ(0, sockopt_get(sk[0], SO_PASSPIDFD));
> +
> +       /* Disabling one option leaves the other alone. */
> +       ASSERT_EQ(0, sockopt_set(sk[0], SO_PASSPIDFD, 0));
> +       ASSERT_EQ(1, sockopt_get(sk[0], SO_PASSPIDFD_THREAD));
> +       ASSERT_EQ(0, sockopt_set(sk[0], SO_PASSPIDFD_THREAD, 0));
> +       ASSERT_EQ(0, sockopt_get(sk[0], SO_PASSPIDFD));
> +       ASSERT_EQ(0, sockopt_get(sk[0], SO_PASSPIDFD_THREAD));
> +
> +       close(sk[0]);
> +       close(sk[1]);
> +}
> +
> +TEST(scm_pidfd_thread)
> +{
> +       struct thread_ids ids;
> +       struct pidfd_info info;
> +
> +       ASSERT_EQ(0, thread_pidfd_flow(send_ids_thread, SO_PASSPIDFD_THREAD,
> +                                      &ids, &info));
> +       ASSERT_NE(ids.pid, ids.tid);
> +       EXPECT_EQ(ids.tid, info.pid);
> +       EXPECT_EQ(ids.pid, info.tgid);
> +}
> +
> +TEST(scm_pidfd_thread_group)
> +{
> +       struct thread_ids ids;
> +       struct pidfd_info info;
> +
> +       ASSERT_EQ(0, thread_pidfd_flow(send_ids_thread, SO_PASSPIDFD,
> +                                      &ids, &info));
> +       ASSERT_NE(ids.pid, ids.tid);
> +       EXPECT_EQ(ids.pid, info.pid);
> +       EXPECT_EQ(ids.pid, info.tgid);
> +}
> +
> +TEST(scm_pidfd_thread_creds)
> +{
> +       struct thread_ids ids;
> +       struct pidfd_info info;
> +
> +       ASSERT_EQ(0, thread_pidfd_flow(send_ids_creds_thread, SO_PASSPIDFD_THREAD,
> +                                      &ids, &info));
> +       ASSERT_NE(ids.pid, ids.tid);
> +       EXPECT_EQ(ids.tid, info.pid);
> +       EXPECT_EQ(ids.pid, info.tgid);
> +}
> +
>  TEST_HARNESS_MAIN
>
> --
> 2.53.0
>

Re: [PATCH 01/10] pid: add helpers to operate on a struct pid array

[Alexander Mikhalitsyn]

Am Mo., 31. Aug. 2026 um 13:21 Uhr schrieb Christian Brauner
<brauner@kernel.org>:
>
> We're about to extend af_unix sockets and coredump code with the ability
> to hand out thread-specific pidfds. Add a few simple helpers that allow
> to operate on multiple struct pids up to PIDTYPE_MAX with automatic
> bounds checking.
>
> Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>

LGTM

Reviewed-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@futurfusion.io>

> ---
>  fs/pidfs.c                   | 16 +++++++++++++
>  include/linux/pid.h          | 53 ++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/pid_types.h    |  8 +++++++
>  include/linux/pidfs.h        |  5 +++++
>  include/linux/sched/signal.h | 18 +++++++++++++++
>  5 files changed, 100 insertions(+)
>
> diff --git a/fs/pidfs.c b/fs/pidfs.c
> index a6a643f15d08..586af2e5811c 100644
> --- a/fs/pidfs.c
> +++ b/fs/pidfs.c
> @@ -1070,6 +1070,22 @@ int pidfs_register_pid_gfp(struct pid *pid, gfp_t gfp)
>         return 0;
>  }
>
> +/* Register the pids up to pid type @last of @pids in pidfs. */
> +int __pidfs_register_pids(struct pid *const *pids, enum pid_type last)
> +{
> +       if (WARN_ON_ONCE(last >= PIDTYPE_MAX))
> +               return -EINVAL;
> +
> +       for (enum pid_type type = PIDTYPE_PID; type <= last; type++) {
> +               int ret = pidfs_register_pid(pids[type]);
> +
> +               if (unlikely(ret))
> +                       return ret;
> +       }
> +
> +       return 0;
> +}
> +
>  static struct dentry *pidfs_stash_dentry(struct dentry **stashed,
>                                          struct dentry *dentry)
>  {
> diff --git a/include/linux/pid.h b/include/linux/pid.h
> index ddaef0bbc8ba..87635d0cc1f7 100644
> --- a/include/linux/pid.h
> +++ b/include/linux/pid.h
> @@ -2,6 +2,9 @@
>  #ifndef _LINUX_PID_H
>  #define _LINUX_PID_H
>
> +#include <linux/array_size.h>
> +#include <linux/build_bug.h>
> +#include <linux/minmax.h>
>  #include <linux/pid_types.h>
>  #include <linux/rculist.h>
>  #include <linux/rcupdate.h>
> @@ -92,6 +95,56 @@ static inline struct pid *get_pid(struct pid *pid)
>  }
>
>  extern void put_pid(struct pid *pid);
> +
> +/*
> + * Helpers for arrays of struct pid indexed by pid type declared with
> + * DECLARE_PIDS(). The array covers PIDTYPE_PID up to the pid type it
> + * was declared with and the helpers take that bound from the array.
> + */
> +static inline void __get_pids(struct pid **dst, struct pid *const *src,
> +                             enum pid_type last)
> +{
> +       for (enum pid_type type = PIDTYPE_PID; type <= last; type++)
> +               dst[type] = get_pid(src[type]);
> +}
> +
> +static inline void __put_pids(struct pid **pids, enum pid_type last)
> +{
> +       for (enum pid_type type = PIDTYPE_PID; type <= last; type++) {
> +               put_pid(pids[type]);
> +               pids[type] = NULL;
> +       }
> +}
> +
> +static inline void __swap_pids(struct pid **a, struct pid **b,
> +                              enum pid_type last)
> +{
> +       for (enum pid_type type = PIDTYPE_PID; type <= last; type++)
> +               swap(a[type], b[type]);
> +}
> +
> +static inline bool __pids_equal(struct pid *const *a, struct pid *const *b,
> +                               enum pid_type last)
> +{
> +       for (enum pid_type type = PIDTYPE_PID; type <= last; type++)
> +               if (a[type] != b[type])
> +                       return false;
> +       return true;
> +}
> +
> +/* The last pid type an array declared with DECLARE_PIDS() covers. */
> +#define pids_last(pids)                                                        \
> +       ((enum pid_type)(ARRAY_SIZE(pids) - 1 +                         \
> +                        BUILD_BUG_ON_ZERO(ARRAY_SIZE(pids) > PIDTYPE_MAX)))
> +
> +#define __pids_last2(a, b)                                             \
> +       (pids_last(a) + BUILD_BUG_ON_ZERO(ARRAY_SIZE(a) != ARRAY_SIZE(b)))
> +
> +#define get_pids(dst, src)     __get_pids(dst, src, __pids_last2(dst, src))
> +#define put_pids(pids)         __put_pids(pids, pids_last(pids))
> +#define swap_pids(a, b)                __swap_pids(a, b, __pids_last2(a, b))
> +#define pids_equal(a, b)       __pids_equal(a, b, __pids_last2(a, b))
> +
>  extern struct task_struct *pid_task(struct pid *pid, enum pid_type);
>  static inline bool pid_has_task(struct pid *pid, enum pid_type type)
>  {
> diff --git a/include/linux/pid_types.h b/include/linux/pid_types.h
> index c2aee1d91dcf..3302690a2a28 100644
> --- a/include/linux/pid_types.h
> +++ b/include/linux/pid_types.h
> @@ -2,6 +2,8 @@
>  #ifndef _LINUX_PID_TYPES_H
>  #define _LINUX_PID_TYPES_H
>
> +#include <linux/build_bug.h>
> +
>  enum pid_type {
>         PIDTYPE_PID,
>         PIDTYPE_TGID,
> @@ -10,6 +12,12 @@ enum pid_type {
>         PIDTYPE_MAX,
>  };
>
> +struct pid;
> +
> +/* An array of struct pid indexed by pid type, PIDTYPE_PID up to @last. */
> +#define DECLARE_PIDS(name, last)                                       \
> +       struct pid *name[(last) + 1 + BUILD_BUG_ON_ZERO((last) >= PIDTYPE_MAX)]
> +
>  struct pid_namespace;
>  extern struct pid_namespace init_pid_ns;
>
> diff --git a/include/linux/pidfs.h b/include/linux/pidfs.h
> index 0abf7da9ab23..3c1e82f1a369 100644
> --- a/include/linux/pidfs.h
> +++ b/include/linux/pidfs.h
> @@ -3,6 +3,7 @@
>  #define _LINUX_PID_FS_H
>
>  #include <linux/gfp_types.h>
> +#include <linux/pid.h>
>
>  struct coredump_params;
>
> @@ -32,5 +33,9 @@ static inline int pidfs_register_pid(struct pid *pid)
>  }
>
>  void pidfs_free_pid(struct pid *pid);
> +int __pidfs_register_pids(struct pid *const *pids, enum pid_type last);
> +
> +/* Register the pids of an array declared with DECLARE_PIDS(). */
> +#define pidfs_register_pids(pids)      __pidfs_register_pids(pids, pids_last(pids))
>
>  #endif /* _LINUX_PID_FS_H */
> diff --git a/include/linux/sched/signal.h b/include/linux/sched/signal.h
> index 584ae88b435e..9444b47789a0 100644
> --- a/include/linux/sched/signal.h
> +++ b/include/linux/sched/signal.h
> @@ -677,6 +677,24 @@ struct pid *task_pid_type(struct task_struct *task, enum pid_type type)
>         return pid;
>  }
>
> +/* Fill @pids with the pid types of @task up to @last, without references. */
> +static inline void __task_pids(struct pid **pids, enum pid_type last,
> +                              struct task_struct *task)
> +{
> +       for (enum pid_type type = PIDTYPE_PID; type <= last; type++)
> +               pids[type] = task_pid_type(task, type);
> +}
> +
> +static inline void __get_task_pids(struct pid **pids, enum pid_type last,
> +                                  struct task_struct *task)
> +{
> +       for (enum pid_type type = PIDTYPE_PID; type <= last; type++)
> +               pids[type] = get_pid(task_pid_type(task, type));
> +}
> +
> +#define task_pids(pids, task)          __task_pids(pids, pids_last(pids), task)
> +#define get_task_pids(pids, task)      __get_task_pids(pids, pids_last(pids), task)
> +
>  static inline struct pid *task_tgid(struct task_struct *task)
>  {
>         return task->signal->pids[PIDTYPE_TGID];
>
> --
> 2.53.0
>

Re: [PATCH 06/10] af_unix: record the pid of the connecting thread

[Alexander Mikhalitsyn]

Am Mo., 31. Aug. 2026 um 13:21 Uhr schrieb Christian Brauner
<brauner@kernel.org>:
>
> Currently only the struct pid of the thread-group leader is recorded.
> The identity of the actual thread that connected to a given socket
> cannot be retrieved.
>
> Add the plumbing to make it possible to retrieve a pidfd for the
> connecting thread. Nothing uses the thread-specific struct pid yet. No
> functional changes.
>
> Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>

LGTM

Reviewed-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@futurfusion.io>

> ---
>  net/unix/af_unix.c | 30 +++++++++++++-----------------
>  1 file changed, 13 insertions(+), 17 deletions(-)
>
> diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
> index 335abd23c9bf..d01ee76c8026 100644
> --- a/net/unix/af_unix.c
> +++ b/net/unix/af_unix.c
> @@ -743,51 +743,47 @@ struct unix_peercred {
>
>  static inline int prepare_peercred(struct unix_peercred *peercred)
>  {
> -       struct pid *pid;
>         int err;
>
> -       pid = task_tgid(current);
> -       err = pidfs_register_pid(pid);
> -       if (likely(!err)) {
> -               peercred->peer_pid[PIDTYPE_TGID] = get_pid(pid);
> -               peercred->peer_cred = get_current_cred();
> +       get_task_pids(peercred->peer_pid, current);
> +       err = pidfs_register_pids(peercred->peer_pid);
> +       if (unlikely(err)) {
> +               put_pids(peercred->peer_pid);
> +               return err;
>         }
> -       return err;
> +
> +       peercred->peer_cred = get_current_cred();
> +       return 0;
>  }
>
>  static void drop_peercred(struct unix_peercred *peercred)
>  {
>         const struct cred *cred = NULL;
> -       struct pid *pid = NULL;
>
>         might_sleep();
>
> -       swap(peercred->peer_pid[PIDTYPE_TGID], pid);
> +       put_pids(peercred->peer_pid);
>         swap(peercred->peer_cred, cred);
> -
> -       put_pid(pid);
>         put_cred(cred);
>  }
>
>  static inline void init_peercred(struct sock *sk,
>                                  const struct unix_peercred *peercred)
>  {
> -       sk->sk_peer_pid[PIDTYPE_TGID] = peercred->peer_pid[PIDTYPE_TGID];
> +       memcpy(sk->sk_peer_pid, peercred->peer_pid, sizeof(sk->sk_peer_pid));
>         sk->sk_peer_cred = peercred->peer_cred;
>  }
>
>  static void update_peercred(struct sock *sk, struct unix_peercred *peercred)
>  {
>         const struct cred *old_cred;
> -       struct pid *old_pid;
>
>         spin_lock(&sk->sk_peer_lock);
> -       old_pid = sk->sk_peer_pid[PIDTYPE_TGID];
> +       swap_pids(sk->sk_peer_pid, peercred->peer_pid);
>         old_cred = sk->sk_peer_cred;
> -       init_peercred(sk, peercred);
> +       sk->sk_peer_cred = peercred->peer_cred;
>         spin_unlock(&sk->sk_peer_lock);
>
> -       peercred->peer_pid[PIDTYPE_TGID] = old_pid;
>         peercred->peer_cred = old_cred;
>  }
>
> @@ -796,7 +792,7 @@ static void copy_peercred(struct sock *sk, struct sock *peersk)
>         lockdep_assert_held(&unix_sk(peersk)->lock);
>
>         spin_lock(&sk->sk_peer_lock);
> -       sk->sk_peer_pid[PIDTYPE_TGID] = get_pid(peersk->sk_peer_pid[PIDTYPE_TGID]);
> +       get_pids(sk->sk_peer_pid, peersk->sk_peer_pid);
>         sk->sk_peer_cred = get_cred(peersk->sk_peer_cred);
>         spin_unlock(&sk->sk_peer_lock);
>  }
>
> --
> 2.53.0
>

Re: [PATCH 07/10] net: add SO_PEERPIDFD_THREAD to get a thread-specific pidfd

[Alexander Mikhalitsyn]

Am Mo., 31. Aug. 2026 um 13:21 Uhr schrieb Christian Brauner
<brauner@kernel.org>:
>
> SO_PEERPIDFD hands out a pidfd for the thread-group that called
> connect() or socketpair(). Enable workloads such as the coredump server
> or a broker to get a pidfd of the specific thread that connected to the
> socket.
>
> Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>

LGTM

Reviewed-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@futurfusion.io>

> ---
>  arch/alpha/include/uapi/asm/socket.h  |  2 +
>  arch/mips/include/uapi/asm/socket.h   |  2 +
>  arch/parisc/include/uapi/asm/socket.h |  2 +
>  arch/sparc/include/uapi/asm/socket.h  |  2 +
>  include/uapi/asm-generic/socket.h     |  2 +
>  net/core/sock.c                       | 87 ++++++++++++++++++++---------------
>  net/unix/af_unix.c                    |  1 +
>  7 files changed, 61 insertions(+), 37 deletions(-)
>
> diff --git a/arch/alpha/include/uapi/asm/socket.h b/arch/alpha/include/uapi/asm/socket.h
> index bb3d534826bb..5d3524c26b2b 100644
> --- a/arch/alpha/include/uapi/asm/socket.h
> +++ b/arch/alpha/include/uapi/asm/socket.h
> @@ -159,6 +159,8 @@
>
>  #define SO_PASSPIDFD_THREAD    86
>
> +#define SO_PEERPIDFD_THREAD    87
> +
>  #if !defined(__KERNEL__)
>
>  #if __BITS_PER_LONG == 64
> diff --git a/arch/mips/include/uapi/asm/socket.h b/arch/mips/include/uapi/asm/socket.h
> index 269badcaa086..245a43f52fb1 100644
> --- a/arch/mips/include/uapi/asm/socket.h
> +++ b/arch/mips/include/uapi/asm/socket.h
> @@ -170,6 +170,8 @@
>
>  #define SO_PASSPIDFD_THREAD    86
>
> +#define SO_PEERPIDFD_THREAD    87
> +
>  #if !defined(__KERNEL__)
>
>  #if __BITS_PER_LONG == 64
> diff --git a/arch/parisc/include/uapi/asm/socket.h b/arch/parisc/include/uapi/asm/socket.h
> index 313aee10a52c..f23710e1c671 100644
> --- a/arch/parisc/include/uapi/asm/socket.h
> +++ b/arch/parisc/include/uapi/asm/socket.h
> @@ -151,6 +151,8 @@
>
>  #define SO_PASSPIDFD_THREAD    0x4054
>
> +#define SO_PEERPIDFD_THREAD    0x4055
> +
>  #if !defined(__KERNEL__)
>
>  #if __BITS_PER_LONG == 64
> diff --git a/arch/sparc/include/uapi/asm/socket.h b/arch/sparc/include/uapi/asm/socket.h
> index bd3e69bcce7a..b35b25bdefc2 100644
> --- a/arch/sparc/include/uapi/asm/socket.h
> +++ b/arch/sparc/include/uapi/asm/socket.h
> @@ -152,6 +152,8 @@
>
>  #define SO_PASSPIDFD_THREAD      0x005f
>
> +#define SO_PEERPIDFD_THREAD      0x0060
> +
>  #if !defined(__KERNEL__)
>
>
> diff --git a/include/uapi/asm-generic/socket.h b/include/uapi/asm-generic/socket.h
> index d1e5c6de146d..56fed7ab27ab 100644
> --- a/include/uapi/asm-generic/socket.h
> +++ b/include/uapi/asm-generic/socket.h
> @@ -154,6 +154,8 @@
>
>  #define SO_PASSPIDFD_THREAD    86
>
> +#define SO_PEERPIDFD_THREAD    87
> +
>  #if !defined(__KERNEL__)
>
>  #if __BITS_PER_LONG == 64 || (defined(__x86_64__) && defined(__ILP32__))
> diff --git a/net/core/sock.c b/net/core/sock.c
> index 6ada7e7eb7d7..cb2ffd329bc6 100644
> --- a/net/core/sock.c
> +++ b/net/core/sock.c
> @@ -1743,6 +1743,50 @@ static int groups_to_user(sockptr_t dst, const struct group_info *src)
>         return 0;
>  }
>
> +/* Hand out a pidfd for @type of the socket's peer via SO_PEERPIDFD*. */
> +static int sk_getsockopt_peerpidfd(struct sock *sk, enum pid_type type,
> +                                  sockptr_t optval, sockptr_t optlen, int len)
> +{
> +       struct file *pidfd_file = NULL;
> +       unsigned int flags = 0;
> +       struct pid *peer_pid;
> +       int pidfd;
> +
> +       if (len > sizeof(pidfd))
> +               len = sizeof(pidfd);
> +
> +       spin_lock(&sk->sk_peer_lock);
> +       peer_pid = get_pid(sk->sk_peer_pid[type]);
> +       spin_unlock(&sk->sk_peer_lock);
> +
> +       if (!peer_pid)
> +               return -ENODATA;
> +
> +       /* The use of PIDFD_STALE requires stashing of struct pid on pidfs
> +        * with pidfs_register_pid() and only AF_UNIX were prepared for this.
> +        */
> +       if (sk->sk_family == AF_UNIX)
> +               flags |= PIDFD_STALE;
> +       if (type == PIDTYPE_PID)
> +               flags |= PIDFD_THREAD;
> +
> +       pidfd = pidfd_prepare(peer_pid, flags, &pidfd_file);
> +       put_pid(peer_pid);
> +       if (pidfd < 0)
> +               return pidfd;
> +
> +       if (copy_to_sockptr(optval, &pidfd, len) ||
> +           copy_to_sockptr(optlen, &len, sizeof(int))) {
> +               put_unused_fd(pidfd);
> +               fput(pidfd_file);
> +
> +               return -EFAULT;
> +       }
> +
> +       fd_install(pidfd, pidfd_file);
> +       return 0;
> +}
> +
>  int sk_getsockopt(struct sock *sk, int level, int optname,
>                   sockptr_t optval, sockptr_t optlen)
>  {
> @@ -1938,45 +1982,14 @@ int sk_getsockopt(struct sock *sk, int level, int optname,
>         }
>
>         case SO_PEERPIDFD:
> -       {
> -               struct pid *peer_pid;
> -               struct file *pidfd_file = NULL;
> -               unsigned int flags = 0;
> -               int pidfd;
> -
> -               if (len > sizeof(pidfd))
> -                       len = sizeof(pidfd);
> -
> -               spin_lock(&sk->sk_peer_lock);
> -               peer_pid = get_pid(sk->sk_peer_pid[PIDTYPE_TGID]);
> -               spin_unlock(&sk->sk_peer_lock);
> -
> -               if (!peer_pid)
> -                       return -ENODATA;
> -
> -               /* The use of PIDFD_STALE requires stashing of struct pid
> -                * on pidfs with pidfs_register_pid() and only AF_UNIX
> -                * were prepared for this.
> -                */
> -               if (sk->sk_family == AF_UNIX)
> -                       flags = PIDFD_STALE;
> +               return sk_getsockopt_peerpidfd(sk, PIDTYPE_TGID, optval, optlen, len);
>
> -               pidfd = pidfd_prepare(peer_pid, flags, &pidfd_file);
> -               put_pid(peer_pid);
> -               if (pidfd < 0)
> -                       return pidfd;
> -
> -               if (copy_to_sockptr(optval, &pidfd, len) ||
> -                   copy_to_sockptr(optlen, &len, sizeof(int))) {
> -                       put_unused_fd(pidfd);
> -                       fput(pidfd_file);
> -
> -                       return -EFAULT;
> -               }
> +       case SO_PEERPIDFD_THREAD:
> +               /* Only AF_UNIX records the peer's connecting thread. */
> +               if (!sk_is_unix(sk))
> +                       return -EOPNOTSUPP;
>
> -               fd_install(pidfd, pidfd_file);
> -               return 0;
> -       }
> +               return sk_getsockopt_peerpidfd(sk, PIDTYPE_PID, optval, optlen, len);
>
>         case SO_PEERGROUPS:
>         {
> diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
> index d01ee76c8026..563d9827c5cc 100644
> --- a/net/unix/af_unix.c
> +++ b/net/unix/af_unix.c
> @@ -1056,6 +1056,7 @@ static bool unix_bpf_bypass_getsockopt(int level, int optname)
>         if (level == SOL_SOCKET) {
>                 switch (optname) {
>                 case SO_PEERPIDFD:
> +               case SO_PEERPIDFD_THREAD:
>                         return true;
>                 default:
>                         return false;
>
> --
> 2.53.0
>

Re: [PATCH 08/10] selftests/net: SO_PEERPIDFD_THREAD

[Alexander Mikhalitsyn]

Am Mo., 31. Aug. 2026 um 13:21 Uhr schrieb Christian Brauner
<brauner@kernel.org>:
>
> Add tests for SO_PEERPIDFD_THREAD.
>
> Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>

LGTM

Reviewed-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@futurfusion.io>

> ---
>  tools/testing/selftests/net/af_unix/scm_pidfd.c | 97 +++++++++++++++++++++++++
>  1 file changed, 97 insertions(+)
>
> diff --git a/tools/testing/selftests/net/af_unix/scm_pidfd.c b/tools/testing/selftests/net/af_unix/scm_pidfd.c
> index 019c48e1cdcd..bbbd5e7b4fa7 100644
> --- a/tools/testing/selftests/net/af_unix/scm_pidfd.c
> +++ b/tools/testing/selftests/net/af_unix/scm_pidfd.c
> @@ -32,6 +32,10 @@
>  #define SO_PASSPIDFD_THREAD 86
>  #endif
>
> +#ifndef SO_PEERPIDFD_THREAD
> +#define SO_PEERPIDFD_THREAD 87
> +#endif
> +
>  #define CHILD_EXIT_CODE_OK 123
>
>  static void child_die()
> @@ -822,4 +826,97 @@ TEST(scm_pidfd_thread_creds)
>         EXPECT_EQ(ids.pid, info.tgid);
>  }
>
> +static void *peer_connect_thread(void *arg)
> +{
> +       struct sock_addr *sa = arg;
> +       struct thread_ids ids = {
> +               .pid = getpid(),
> +               .tid = gettid(),
> +       };
> +       int fd;
> +       char sync;
> +
> +       fd = socket(AF_UNIX, SOCK_STREAM, 0);
> +       if (fd < 0)
> +               return (void *)1;
> +
> +       if (connect(fd, (struct sockaddr *)&sa->listen_addr, sa->addrlen))
> +               return (void *)1;
> +
> +       if (send(fd, &ids, sizeof(ids), 0) != sizeof(ids))
> +               return (void *)1;
> +
> +       /* stay alive until the server has looked at our pidfd */
> +       if (read(fd, &sync, 1) != 1)
> +               return (void *)1;
> +
> +       close(fd);
> +       return NULL;
> +}
> +
> +static int peer_pidfd_info(int fd, int optname, struct pidfd_info *info)
> +{
> +       int pidfd;
> +       socklen_t len = sizeof(pidfd);
> +
> +       if (getsockopt(fd, SOL_SOCKET, optname, &pidfd, &len)) {
> +               log_err("getsockopt(SO_PEERPIDFD*)");
> +               return -1;
> +       }
> +
> +       info->mask = PIDFD_INFO_PID;
> +       if (ioctl(pidfd, PIDFD_GET_INFO, info)) {
> +               log_err("ioctl(PIDFD_GET_INFO)");
> +               close(pidfd);
> +               return -1;
> +       }
> +
> +       close(pidfd);
> +       return 0;
> +}
> +
> +/* SO_PEERPIDFD_THREAD returns a pidfd for the peer's connecting thread. */
> +TEST(so_peerpidfd_thread)
> +{
> +       struct sock_addr sa;
> +       struct thread_ids ids;
> +       struct pidfd_info info;
> +       pthread_t thread;
> +       void *tret;
> +       int server, cfd;
> +
> +       server = socket(AF_UNIX, SOCK_STREAM, 0);
> +       ASSERT_LE(0, server);
> +
> +       fill_sockaddr(&sa, true);
> +       ASSERT_EQ(0, bind(server, (struct sockaddr *)&sa.listen_addr, sa.addrlen));
> +       ASSERT_EQ(0, listen(server, 1));
> +
> +       ASSERT_EQ(0, pthread_create(&thread, NULL, peer_connect_thread, &sa));
> +
> +       cfd = accept(server, NULL, NULL);
> +       ASSERT_LE(0, cfd);
> +
> +       ASSERT_EQ(sizeof(ids), recv(cfd, &ids, sizeof(ids), MSG_WAITALL));
> +       ASSERT_NE(ids.pid, ids.tid);
> +
> +       /* SO_PEERPIDFD refers to the peer's thread-group. */
> +       ASSERT_EQ(0, peer_pidfd_info(cfd, SO_PEERPIDFD, &info));
> +       EXPECT_EQ(ids.pid, info.pid);
> +       EXPECT_EQ(ids.pid, info.tgid);
> +
> +       /* SO_PEERPIDFD_THREAD refers to the connecting thread. */
> +       ASSERT_EQ(0, peer_pidfd_info(cfd, SO_PEERPIDFD_THREAD, &info));
> +       EXPECT_EQ(ids.tid, info.pid);
> +       EXPECT_EQ(ids.pid, info.tgid);
> +
> +       /* release the connecting thread */
> +       ASSERT_EQ(1, write(cfd, "x", 1));
> +       ASSERT_EQ(0, pthread_join(thread, &tret));
> +       ASSERT_EQ(NULL, tret);
> +
> +       close(cfd);
> +       close(server);
> +}
> +
>  TEST_HARNESS_MAIN
>
> --
> 2.53.0
>

Re: [PATCH 09/10] pidfs: record the coredump on the dumping thread's pid too

[Alexander Mikhalitsyn]

Am Mo., 31. Aug. 2026 um 13:22 Uhr schrieb Christian Brauner
<brauner@kernel.org>:
>
> If a thread-group coredumps only the thread-group leader pidfd will
> return coredump information. A pidfd for the thread that took the fatal
> signal cannot be used to retrieve it.
>
> Record both the thread-group leader and the specific thread that took
> the signal and register both in pidfs. Mark both the thread-group leader
> and the specific thread with the coredump information so retrieval works
> for both pidfds.
>
> Now that both SO_PEERPIDFD and SO_PEERPIDFD_THREAD are available it's
> easy to get the coredump information for the specific thread.
>
> Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>

LGTM

Reviewed-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@futurfusion.io>

> ---
>  fs/coredump.c            | 22 +++++++++++++---------
>  fs/pidfs.c               | 11 +++++++++--
>  include/linux/coredump.h |  4 +++-
>  3 files changed, 25 insertions(+), 12 deletions(-)
>
> diff --git a/fs/coredump.c b/fs/coredump.c
> index 71a0093ada1b..b5ff4b3e1831 100644
> --- a/fs/coredump.c
> +++ b/fs/coredump.c
> @@ -454,7 +454,7 @@ static bool coredump_parse(struct core_name *cn, struct coredump_params *cprm,
>                                  * leader we know that the thread-group leader
>                                  * cannot be reaped until @current has exited.
>                                  */
> -                               cprm->pid = task_tgid(current);
> +                               task_pids(cprm->pid, current);
>                                 err = cn_printf(cn, "%d", COREDUMP_PIDFD_NUMBER);
>                                 break;
>                         }
> @@ -626,13 +626,17 @@ static int umh_coredump_setup(struct subprocess_info *info, struct cred *new)
>         struct coredump_params *cp = (struct coredump_params *)info->data;
>         int err;
>
> -       if (cp->pid) {
> +       if (cp->pid[PIDTYPE_TGID]) {
>                 struct file *pidfs_file __free(fput) = NULL;
>
> -               pidfs_file = pidfs_alloc_file(cp->pid, 0);
> +               pidfs_file = pidfs_alloc_file(cp->pid[PIDTYPE_TGID], 0);
>                 if (IS_ERR(pidfs_file))
>                         return PTR_ERR(pidfs_file);
>
> +               err = pidfs_register_pids(cp->pid);
> +               if (err)
> +                       return err;
> +
>                 pidfs_coredump(cp);
>
>                 /*
> @@ -695,12 +699,12 @@ static bool coredump_sock_connect(struct core_name *cn, struct coredump_params *
>                 return false;
>
>         /*
> -        * Set the thread-group leader pid which is used for the peer
> -        * credentials during connect() below. Then immediately register
> -        * it in pidfs...
> +        * Set the pids of the dumping thread and its thread-group leader
> +        * which are used for the peer credentials during connect() below.
> +        * Then immediately register them in pidfs...
>          */
> -       cprm->pid = task_tgid(current);
> -       retval = pidfs_register_pid(cprm->pid);
> +       task_pids(cprm->pid, current);
> +       retval = pidfs_register_pids(cprm->pid);
>         if (retval)
>                 return false;
>
> @@ -722,7 +726,7 @@ static bool coredump_sock_connect(struct core_name *cn, struct coredump_params *
>         }
>
>         /* ... and validate that @sk_peer_pid matches @cprm.pid. */
> -       if (WARN_ON_ONCE(unix_peer(socket->sk)->sk_peer_pid[PIDTYPE_TGID] != cprm->pid))
> +       if (WARN_ON_ONCE(!pids_equal(unix_peer(socket->sk)->sk_peer_pid, cprm->pid)))
>                 return false;
>
>         cprm->limit = RLIM_INFINITY;
> diff --git a/fs/pidfs.c b/fs/pidfs.c
> index 586af2e5811c..29299b2c7ca7 100644
> --- a/fs/pidfs.c
> +++ b/fs/pidfs.c
> @@ -793,9 +793,9 @@ void pidfs_exit(struct task_struct *tsk)
>  }
>
>  #ifdef CONFIG_COREDUMP
> -void pidfs_coredump(const struct coredump_params *cprm)
> +static void pidfs_coredump_pid(struct pid *pid,
> +                              const struct coredump_params *cprm)
>  {
> -       struct pid *pid = cprm->pid;
>         struct pidfs_attr *attr;
>
>         attr = READ_ONCE(pid->attr);
> @@ -814,6 +814,13 @@ void pidfs_coredump(const struct coredump_params *cprm)
>         smp_wmb();
>         set_bit(PIDFS_ATTR_BIT_COREDUMP, &attr->attr_mask);
>  }
> +
> +void pidfs_coredump(const struct coredump_params *cprm)
> +{
> +       /* The dumping thread's pidfd reports the coredump as well. */
> +       for (enum pid_type type = PIDTYPE_PID; type <= pids_last(cprm->pid); type++)
> +               pidfs_coredump_pid(cprm->pid[type], cprm);
> +}
>  #endif
>
>  static struct vfsmount *pidfs_mnt __ro_after_init;
> diff --git a/include/linux/coredump.h b/include/linux/coredump.h
> index 7b38ee2e7913..0bbb7de6a402 100644
> --- a/include/linux/coredump.h
> +++ b/include/linux/coredump.h
> @@ -5,6 +5,7 @@
>  #include <linux/types.h>
>  #include <linux/mm.h>
>  #include <linux/fs.h>
> +#include <linux/pid_types.h>
>  #include <linux/sched/coredump.h>
>  #include <asm/siginfo.h>
>
> @@ -32,7 +33,8 @@ struct coredump_params {
>         int vma_count;
>         size_t vma_data_size;
>         struct core_vma_metadata *vma_meta;
> -       struct pid *pid;
> +       /* Dumping thread and its thread-group leader by pid type. */
> +       DECLARE_PIDS(pid, PIDTYPE_TGID);
>  };
>
>  extern unsigned int core_file_note_size_limit;
>
> --
> 2.53.0
>

Re: [PATCH 10/10] selftests/coredump: check the dumping thread's pidfd

[Alexander Mikhalitsyn]

Am Mo., 31. Aug. 2026 um 13:22 Uhr schrieb Christian Brauner
<brauner@kernel.org>:
>
> Crash from a non-leader thread and verify that the pidfd from
> SO_PEERPIDFD_THREAD on the coredump socket refers to that thread and
> reports the coredump like the thread-group leader's pidfd does.
>
> Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>

LGTM

Reviewed-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@futurfusion.io>

> ---
>  .../selftests/coredump/coredump_socket_test.c      | 175 +++++++++++++++++++++
>  tools/testing/selftests/coredump/coredump_test.h   |   2 +
>  .../selftests/coredump/coredump_test_helpers.c     |  49 ++++++
>  3 files changed, 226 insertions(+)
>
> diff --git a/tools/testing/selftests/coredump/coredump_socket_test.c b/tools/testing/selftests/coredump/coredump_socket_test.c
> index 422728f632ca..ec73bb690bbc 100644
> --- a/tools/testing/selftests/coredump/coredump_socket_test.c
> +++ b/tools/testing/selftests/coredump/coredump_socket_test.c
> @@ -592,6 +592,181 @@ TEST_F(coredump, socket_coredump_signal_sigsegv)
>         wait_and_check_coredump_server(pid_coredump_server, _metadata, self);
>  }
>
> +static bool check_coredump_info(const struct pidfd_info *info, const char *what)
> +{
> +       if (!(info->mask & PIDFD_INFO_COREDUMP)) {
> +               fprintf(stderr, "%s: PIDFD_INFO_COREDUMP not set in mask\n", what);
> +               return false;
> +       }
> +
> +       if (!(info->coredump_mask & PIDFD_COREDUMPED)) {
> +               fprintf(stderr, "%s: PIDFD_COREDUMPED not set in coredump_mask\n", what);
> +               return false;
> +       }
> +
> +       if (!(info->mask & PIDFD_INFO_COREDUMP_SIGNAL) || info->coredump_signal != SIGSEGV) {
> +               fprintf(stderr, "%s: coredump_signal=%d, expected SIGSEGV=%d\n",
> +                       what, info->coredump_signal, SIGSEGV);
> +               return false;
> +       }
> +
> +       if (!(info->mask & PIDFD_INFO_COREDUMP_CODE) || info->coredump_code != SEGV_MAPERR) {
> +               fprintf(stderr, "%s: coredump_code=%d, expected SEGV_MAPERR=%d\n",
> +                       what, info->coredump_code, SEGV_MAPERR);
> +               return false;
> +       }
> +
> +       return true;
> +}
> +
> +/*
> + * Test: PIDFD_INFO_COREDUMP on the dumping thread's pidfd
> + *
> + * Crash from a non-leader thread and verify that the pidfd from
> + * SO_PEERPIDFD_THREAD refers to that thread and reports the coredump
> + * like the thread-group leader's pidfd from SO_PEERPIDFD does.
> + */
> +TEST_F(coredump, socket_coredump_thread)
> +{
> +       int pidfd, ret, status;
> +       pid_t pid, pid_coredump_server;
> +       struct pidfd_info info = {};
> +       int ipc_sockets[2];
> +       char c;
> +
> +       ASSERT_TRUE(set_core_pattern("@/tmp/coredump.socket"));
> +
> +       ret = socketpair(AF_UNIX, SOCK_STREAM | SOCK_CLOEXEC, 0, ipc_sockets);
> +       ASSERT_EQ(ret, 0);
> +
> +       pid_coredump_server = fork();
> +       ASSERT_GE(pid_coredump_server, 0);
> +       if (pid_coredump_server == 0) {
> +               int fd_server = -1, fd_coredump = -1, fd_peer_pidfd = -1;
> +               int fd_thread_pidfd = -1, fd_core_file = -1;
> +               struct pidfd_info thread_info = {};
> +               int exit_code = EXIT_FAILURE;
> +
> +               close(ipc_sockets[0]);
> +
> +               fd_server = create_and_listen_unix_socket("/tmp/coredump.socket");
> +               if (fd_server < 0) {
> +                       fprintf(stderr, "socket_coredump_thread: listen socket failed: %m\n");
> +                       goto out;
> +               }
> +
> +               if (write_nointr(ipc_sockets[1], "1", 1) < 0) {
> +                       fprintf(stderr, "socket_coredump_thread: ipc write failed: %m\n");
> +                       goto out;
> +               }
> +
> +               close(ipc_sockets[1]);
> +
> +               fd_coredump = accept4(fd_server, NULL, NULL, SOCK_CLOEXEC);
> +               if (fd_coredump < 0) {
> +                       fprintf(stderr, "socket_coredump_thread: accept4 failed: %m\n");
> +                       goto out;
> +               }
> +
> +               fd_peer_pidfd = get_peer_pidfd(fd_coredump);
> +               if (fd_peer_pidfd < 0) {
> +                       fprintf(stderr, "socket_coredump_thread: get_peer_pidfd failed\n");
> +                       goto out;
> +               }
> +
> +               fd_thread_pidfd = get_peer_pidfd_thread(fd_coredump);
> +               if (fd_thread_pidfd < 0) {
> +                       fprintf(stderr, "socket_coredump_thread: get_peer_pidfd_thread failed\n");
> +                       goto out;
> +               }
> +
> +               if (!get_pidfd_info(fd_peer_pidfd, &info) ||
> +                   !get_pidfd_info(fd_thread_pidfd, &thread_info)) {
> +                       fprintf(stderr, "socket_coredump_thread: get_pidfd_info failed\n");
> +                       goto out;
> +               }
> +
> +               /* The peer is the thread-group leader, the dumping thread is not. */
> +               if (info.pid != info.tgid || thread_info.tgid != info.tgid ||
> +                   thread_info.pid == thread_info.tgid) {
> +                       fprintf(stderr, "socket_coredump_thread: unexpected ids %d/%d and %d/%d\n",
> +                               info.pid, info.tgid, thread_info.pid, thread_info.tgid);
> +                       goto out;
> +               }
> +
> +               if (!check_coredump_info(&info, "SO_PEERPIDFD") ||
> +                   !check_coredump_info(&thread_info, "SO_PEERPIDFD_THREAD"))
> +                       goto out;
> +
> +               fd_core_file = open_coredump_tmpfile(self->fd_tmpfs_detached);
> +               if (fd_core_file < 0) {
> +                       fprintf(stderr, "socket_coredump_thread: core tmpfile failed: %m\n");
> +                       goto out;
> +               }
> +
> +               for (;;) {
> +                       char buffer[4096];
> +                       ssize_t bytes_read, bytes_write;
> +
> +                       bytes_read = read(fd_coredump, buffer, sizeof(buffer));
> +                       if (bytes_read < 0) {
> +                               fprintf(stderr, "socket_coredump_thread: core read failed: %m\n");
> +                               goto out;
> +                       }
> +
> +                       if (bytes_read == 0)
> +                               break;
> +
> +                       bytes_write = write(fd_core_file, buffer, bytes_read);
> +                       if (bytes_read != bytes_write) {
> +                               fprintf(stderr, "socket_coredump_thread: core write %zd/%zd: %m\n",
> +                                       bytes_read, bytes_write);
> +                               goto out;
> +                       }
> +               }
> +
> +               exit_code = EXIT_SUCCESS;
> +               fprintf(stderr, "socket_coredump_thread: completed successfully\n");
> +out:
> +               if (fd_core_file >= 0)
> +                       close(fd_core_file);
> +               if (fd_thread_pidfd >= 0)
> +                       close(fd_thread_pidfd);
> +               if (fd_peer_pidfd >= 0)
> +                       close(fd_peer_pidfd);
> +               if (fd_coredump >= 0)
> +                       close(fd_coredump);
> +               if (fd_server >= 0)
> +                       close(fd_server);
> +               _exit(exit_code);
> +       }
> +       self->pid_coredump_server = pid_coredump_server;
> +
> +       EXPECT_EQ(close(ipc_sockets[1]), 0);
> +       ASSERT_EQ(read_nointr(ipc_sockets[0], &c, 1), 1);
> +       EXPECT_EQ(close(ipc_sockets[0]), 0);
> +
> +       pid = fork();
> +       ASSERT_GE(pid, 0);
> +       if (pid == 0)
> +               crashing_child_thread();
> +
> +       pidfd = sys_pidfd_open(pid, 0);
> +       ASSERT_GE(pidfd, 0);
> +
> +       waitpid(pid, &status, 0);
> +       ASSERT_TRUE(WIFSIGNALED(status));
> +       ASSERT_EQ(WTERMSIG(status), SIGSEGV);
> +       ASSERT_TRUE(WCOREDUMP(status));
> +
> +       ASSERT_TRUE(get_pidfd_info(pidfd, &info));
> +       ASSERT_TRUE(!!(info.mask & PIDFD_INFO_COREDUMP));
> +       ASSERT_TRUE(!!(info.coredump_mask & PIDFD_COREDUMPED));
> +       ASSERT_EQ(info.coredump_signal, SIGSEGV);
> +
> +       wait_and_check_coredump_server(pid_coredump_server, _metadata, self);
> +}
> +
>  /*
>   * Test: PIDFD_INFO_COREDUMP_SIGNAL via simple socket coredump with SIGABRT
>   *
> diff --git a/tools/testing/selftests/coredump/coredump_test.h b/tools/testing/selftests/coredump/coredump_test.h
> index ed47f01fa53c..4212656e31f0 100644
> --- a/tools/testing/selftests/coredump/coredump_test.h
> +++ b/tools/testing/selftests/coredump/coredump_test.h
> @@ -27,10 +27,12 @@ FIXTURE(coredump)
>  /* Shared helper function declarations */
>  void *do_nothing(void *arg);
>  void crashing_child(void);
> +void crashing_child_thread(void);
>  int create_detached_tmpfs(void);
>  int create_and_listen_unix_socket(const char *path);
>  bool set_core_pattern(const char *pattern);
>  int get_peer_pidfd(int fd);
> +int get_peer_pidfd_thread(int fd);
>  bool get_pidfd_info(int fd_peer_pidfd, struct pidfd_info *info);
>
>  /* Inline helper that uses harness types */
> diff --git a/tools/testing/selftests/coredump/coredump_test_helpers.c b/tools/testing/selftests/coredump/coredump_test_helpers.c
> index 2a20faf9cb0a..36306069f62e 100644
> --- a/tools/testing/selftests/coredump/coredump_test_helpers.c
> +++ b/tools/testing/selftests/coredump/coredump_test_helpers.c
> @@ -13,6 +13,7 @@
>  #include <string.h>
>  #include <sys/epoll.h>
>  #include <sys/ioctl.h>
> +#include <sys/mman.h>
>  #include <sys/socket.h>
>  #include <sys/types.h>
>  #include <sys/un.h>
> @@ -38,6 +39,10 @@ struct _fixture_coredump_data {
>
>  #define NUM_THREAD_SPAWN 128
>
> +#ifndef SO_PEERPIDFD_THREAD
> +#define SO_PEERPIDFD_THREAD 87
> +#endif
> +
>  void *do_nothing(void *arg)
>  {
>         (void)arg;
> @@ -59,6 +64,36 @@ void crashing_child(void)
>         i = *(volatile int *)NULL;
>  }
>
> +static void *crashing_thread(void *arg)
> +{
> +       int *p;
> +
> +       (void)arg;
> +
> +       /* crash on purpose with SEGV_MAPERR */
> +       p = mmap(NULL, PAGE_SIZE, PROT_READ | PROT_WRITE,
> +                MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
> +       if (p == MAP_FAILED)
> +               return NULL;
> +       munmap(p, PAGE_SIZE);
> +       *p = 0;
> +
> +       return NULL;
> +}
> +
> +void crashing_child_thread(void)
> +{
> +       pthread_t thread;
> +       int i;
> +
> +       for (i = 0; i < NUM_THREAD_SPAWN; ++i)
> +               pthread_create(&thread, NULL, do_nothing, NULL);
> +
> +       /* crash from a non-leader thread */
> +       pthread_create(&thread, NULL, crashing_thread, NULL);
> +       pause();
> +}
> +
>  int create_detached_tmpfs(void)
>  {
>         int fd_context, fd_tmpfs;
> @@ -138,6 +173,20 @@ int get_peer_pidfd(int fd)
>         return fd_peer_pidfd;
>  }
>
> +int get_peer_pidfd_thread(int fd)
> +{
> +       int fd_peer_pidfd;
> +       socklen_t fd_peer_pidfd_len = sizeof(fd_peer_pidfd);
> +       int ret = getsockopt(fd, SOL_SOCKET, SO_PEERPIDFD_THREAD, &fd_peer_pidfd,
> +                            &fd_peer_pidfd_len);
> +       if (ret < 0) {
> +               fprintf(stderr, "%s: getsockopt(SO_PEERPIDFD_THREAD) failed: %m\n", __func__);
> +               return -1;
> +       }
> +       fprintf(stderr, "%s: successfully retrieved pidfd %d\n", __func__, fd_peer_pidfd);
> +       return fd_peer_pidfd;
> +}
> +
>  bool get_pidfd_info(int fd_peer_pidfd, struct pidfd_info *info)
>  {
>         int ret;
>
> --
> 2.53.0
>

Re: [PATCH 02/10] af_unix: record the pid of the sending thread

[Christian Brauner]

On Mon, Sep 07, 2026 at 11:55:23AM +0200, Alexander Mikhalitsyn wrote:
> Am Mo., 31. Aug. 2026 um 13:21 Uhr schrieb Christian Brauner
> <brauner@kernel.org>:
> >
> > Currently only the struct pid of the thread-group leader is recorded.
> > The identity of the actual thread that sent the message or is connected
> > to a given socket cannot be retrieved.
> >
> > Add the plumbing to make it possible to retrieve a pidfd for the sender.
> > Nothing uses the thread-specific struct pid yet. No functional changes.
> >
> > Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
> > ---
> >  include/net/scm.h  |  7 +++----
> >  net/core/scm.c     | 21 +++++++++++++++++----
> >  net/unix/af_unix.c | 23 +++++++++++++----------
> >  net/unix/af_unix.h |  3 ++-
> >  4 files changed, 35 insertions(+), 19 deletions(-)
> >
> > diff --git a/include/net/scm.h b/include/net/scm.h
> > index 86ae6bc109ec..aa7d15c5fc27 100644
> > --- a/include/net/scm.h
> > +++ b/include/net/scm.h
> > @@ -42,7 +42,7 @@ struct scm_fp_list {
> >  };
> >
> >  struct scm_cookie {
> > -       struct pid              *pid;           /* Skb credentials */
> > +       DECLARE_PIDS(pid, PIDTYPE_TGID);        /* Skb credentials by pid type */
> >         struct scm_fp_list      *fp;            /* Passed files         */
> >         struct scm_creds        creds;          /* Skb credentials      */
> >  #ifdef CONFIG_SECURITY_NETWORK
> > @@ -69,7 +69,7 @@ static __inline__ void unix_get_peersec_dgram(struct socket *sock, struct scm_co
> >  static __inline__ void scm_set_cred(struct scm_cookie *scm,
> >                                     struct pid *pid, kuid_t uid, kgid_t gid)
> >  {
> > -       scm->pid = get_pid(pid);
> > +       scm->pid[PIDTYPE_TGID] = get_pid(pid);
> >         scm->creds.pid = pid_vnr(pid);
> >         scm->creds.uid = uid;
> >         scm->creds.gid = gid;
> > @@ -77,8 +77,7 @@ static __inline__ void scm_set_cred(struct scm_cookie *scm,
> >
> >  static __inline__ void scm_destroy_cred(struct scm_cookie *scm)
> >  {
> > -       put_pid(scm->pid);
> > -       scm->pid = NULL;
> > +       put_pids(scm->pid);
> >  }
> >
> >  static __inline__ void scm_destroy(struct scm_cookie *scm)
> > diff --git a/net/core/scm.c b/net/core/scm.c
> > index f0d44ecdb11f..9b9e119c353a 100644
> > --- a/net/core/scm.c
> > +++ b/net/core/scm.c
> > @@ -149,6 +149,7 @@ EXPORT_SYMBOL(__scm_destroy);
> >
> >  static inline int scm_replace_pid(struct scm_cookie *scm, struct pid *pid)
> >  {
> > +       struct pid *thread_pid;
> >         int err;
> >
> >         /* drop all previous references */
> > @@ -158,7 +159,18 @@ static inline int scm_replace_pid(struct scm_cookie *scm, struct pid *pid)
> >         if (unlikely(err))
> >                 return err;
> >
> > -       scm->pid = pid;
> > +       /* A sender naming its own thread-group sends from the current thread. */
> > +       if (pid == task_tgid(current))
> > +               thread_pid = task_pid(current);
> > +       else
> > +               thread_pid = pid;
> 
> Hi Christian,
> 
> The patch looks good to me, but this spot raised some doubts for me.
> 
> If scm_replace_pid() is called with pid == task_tgid(current) then all
> good, because we
> get scm->pid[PIDTYPE_TGID] == pid and  scm->pid[PIDTYPE_PID] ==
> task_pid(current). All good.
> 
> If scm_replace_pid() is supplied with pid that has a type PIDTYPE_TGID, then:
> - scm->pid[PIDTYPE_TGID] == pid. Good.
> - scm->pid[PIDTYPE_PID] = pid. Doesn't looks correct, shoudn't we do

After chatting with you, I think I get the concern. You think that
scm->pid[PIDTYPE_PID] always points to a thread-group leader if pid ==
task_tgid(current). Yes, that's true but that's intended and fine. The
thread-group leader is just a thread in the thread-group just with
magical behavior (that we would really like to get rid of but can't
easily...).

Thanks for looking closely at this though!

Re: [PATCH 02/10] af_unix: record the pid of the sending thread

[Alexander Mikhalitsyn]

Am Mi., 9. Sept. 2026 um 12:36 Uhr schrieb Christian Brauner
<brauner@kernel.org>:
>
> On Mon, Sep 07, 2026 at 11:55:23AM +0200, Alexander Mikhalitsyn wrote:
> > Am Mo., 31. Aug. 2026 um 13:21 Uhr schrieb Christian Brauner
> > <brauner@kernel.org>:
> > >
> > > Currently only the struct pid of the thread-group leader is recorded.
> > > The identity of the actual thread that sent the message or is connected
> > > to a given socket cannot be retrieved.
> > >
> > > Add the plumbing to make it possible to retrieve a pidfd for the sender.
> > > Nothing uses the thread-specific struct pid yet. No functional changes.
> > >
> > > Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
> > > ---
> > >  include/net/scm.h  |  7 +++----
> > >  net/core/scm.c     | 21 +++++++++++++++++----
> > >  net/unix/af_unix.c | 23 +++++++++++++----------
> > >  net/unix/af_unix.h |  3 ++-
> > >  4 files changed, 35 insertions(+), 19 deletions(-)
> > >
> > > diff --git a/include/net/scm.h b/include/net/scm.h
> > > index 86ae6bc109ec..aa7d15c5fc27 100644
> > > --- a/include/net/scm.h
> > > +++ b/include/net/scm.h
> > > @@ -42,7 +42,7 @@ struct scm_fp_list {
> > >  };
> > >
> > >  struct scm_cookie {
> > > -       struct pid              *pid;           /* Skb credentials */
> > > +       DECLARE_PIDS(pid, PIDTYPE_TGID);        /* Skb credentials by pid type */
> > >         struct scm_fp_list      *fp;            /* Passed files         */
> > >         struct scm_creds        creds;          /* Skb credentials      */
> > >  #ifdef CONFIG_SECURITY_NETWORK
> > > @@ -69,7 +69,7 @@ static __inline__ void unix_get_peersec_dgram(struct socket *sock, struct scm_co
> > >  static __inline__ void scm_set_cred(struct scm_cookie *scm,
> > >                                     struct pid *pid, kuid_t uid, kgid_t gid)
> > >  {
> > > -       scm->pid = get_pid(pid);
> > > +       scm->pid[PIDTYPE_TGID] = get_pid(pid);
> > >         scm->creds.pid = pid_vnr(pid);
> > >         scm->creds.uid = uid;
> > >         scm->creds.gid = gid;
> > > @@ -77,8 +77,7 @@ static __inline__ void scm_set_cred(struct scm_cookie *scm,
> > >
> > >  static __inline__ void scm_destroy_cred(struct scm_cookie *scm)
> > >  {
> > > -       put_pid(scm->pid);
> > > -       scm->pid = NULL;
> > > +       put_pids(scm->pid);
> > >  }
> > >
> > >  static __inline__ void scm_destroy(struct scm_cookie *scm)
> > > diff --git a/net/core/scm.c b/net/core/scm.c
> > > index f0d44ecdb11f..9b9e119c353a 100644
> > > --- a/net/core/scm.c
> > > +++ b/net/core/scm.c
> > > @@ -149,6 +149,7 @@ EXPORT_SYMBOL(__scm_destroy);
> > >
> > >  static inline int scm_replace_pid(struct scm_cookie *scm, struct pid *pid)
> > >  {
> > > +       struct pid *thread_pid;
> > >         int err;
> > >
> > >         /* drop all previous references */
> > > @@ -158,7 +159,18 @@ static inline int scm_replace_pid(struct scm_cookie *scm, struct pid *pid)
> > >         if (unlikely(err))
> > >                 return err;
> > >
> > > -       scm->pid = pid;
> > > +       /* A sender naming its own thread-group sends from the current thread. */
> > > +       if (pid == task_tgid(current))
> > > +               thread_pid = task_pid(current);
> > > +       else
> > > +               thread_pid = pid;
> >
> > Hi Christian,
> >
> > The patch looks good to me, but this spot raised some doubts for me.
> >
> > If scm_replace_pid() is called with pid == task_tgid(current) then all
> > good, because we
> > get scm->pid[PIDTYPE_TGID] == pid and  scm->pid[PIDTYPE_PID] ==
> > task_pid(current). All good.
> >
> > If scm_replace_pid() is supplied with pid that has a type PIDTYPE_TGID, then:
> > - scm->pid[PIDTYPE_TGID] == pid. Good.
> > - scm->pid[PIDTYPE_PID] = pid. Doesn't looks correct, shoudn't we do
>
> After chatting with you, I think I get the concern. You think that
> scm->pid[PIDTYPE_PID] always points to a thread-group leader if pid ==
> task_tgid(current). Yes, that's true but that's intended and fine. The
> thread-group leader is just a thread in the thread-group just with
> magical behavior (that we would really like to get rid of but can't
> easily...).

Yes, my concern was about another case when `pid != task_tgid(current)`, but the
chunk of code I've suggested makes no sense. When I looked at it with
a fresh head I realized this.
In scm_replace_pid, once we've got `pid` pointing to a leader's thread
we can't really do anything
other than taking leader thread's TID as a scm->pid[PIDTYPE_PID]...

>
> Thanks for looking closely at this though!

LGTM

Reviewed-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@futurfusion.io>