[PATCH v2 07/10] net: add SO_PEERPIDFD_THREAD to get a thread-specific pidfd

[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>
---
 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