[PATCH can-next v3 0/3] Introduce diag support for CAN

[PATCH can-next v3 0/3] Introduce diag support for CAN

[Filippo Storniolo]

In the current state of the art, it is not possible for userspace to use
tool like ss(8) to query open AF_CAN sockets.

This patch series adds the netlink can_diag interface for AF_CAN. Userspace
is  now able to send a netlink request to request information about open
AF_CAN sockets that are retrieved by the can-diag.ko module.

Patch 1 is a fix that is mandatory to the correct behaviour of the diag
module: the field sk_protocol is not assigned during `can_create()` instead
of being assigned only in case the CAN socket belong to the j1939 transport
protocol. This is needed to the correct filtering of the can diag module.

Patch 2 introduces a list per network namespace containing open CAN sockets.
The list is protected by a mutex.
CAN sockets are added in `can_create()` to the list and removed from it
in the `release()` calls defined for each transport protocol.

Patch 3 is the core patch that introduces the userspace structures to query
and receive netlink messages for CAN sockets and the actual CAN diag module.
The latter will use the userspace structures defined in <linux/can/diag.h>
to filter and retrieve open CAN sockets.

In the current implementation, every CAN sockets in the list is
returned to the userspace, however a filtering could be implemented:
Userspace could possibly request only bound CAN sockets or CAN sockets
belonging to a specific transport protocol (raw, iso-tp, j1939, bcm)
and so on.

An example of the output given by ss -cpe:

Netid                     Recv-Q                 Send-Q                                 Local Address:Port                                   Peer Address:Port                 Process                                                                 
CAN_ISOTP                 0                      0                                              vcan1:1110                                          vcan1:291                   uid:1001 ino:50324 sk:0 users:(("can2",pid=9210,fd=4))                 
CAN_ISOTP                 0                      0                                              vcan1:291                                           vcan1:1110                  uid:1001 ino:50323 sk:0 users:(("can2",pid=9210,fd=3))

---
Changes in v3:
- Rebased to latest net-next
- Changed no-op functions from #define to static inline
  (Marc Kleine-Budde)
- In struct can_diag_req, sdiag_protocol changed from
  __u8 to __u16. Padding changed accordingly
- Added	CDIAG_SHOW_UID filter in UAPI header and implemented
  filter as netlink attribute in diag module.
- Split sockaddr_can into individual netlink attributes
  for isotp and j1939 respectively, instead of binary-encoding
  it into a single attribute (Sashiko-bot / Marc Kleine-Budde)
- Fixed indentation in /netns/can.h (Marc Kleine-Budde)
- Link to v2: https://lore.kernel.org/r/20260806-feat-can-diag-v2-0-832597ee4cb9@redhat.com

Changes in v2:
- Rebased to latest net-next
- Added a patch, suggested by sashiko-bot, that fixes an attempt
   to lock an uninitialized mutex
- Link to v1: https://lore.kernel.org/r/20260610-feat-can-diag-v1-0-021e3f1631a0@redhat.com

Change w.r.t. RFC:
- header relocation, from linux/can_diag.h to linux/can/diag.h
  (Oliver Hartkopp)
- file renaming, from net/can/can-diag.c to net/can/diag.c
  (Oliver Hartkopp)
- guard renaming, from _UAPI__CAN_DIAG_H__ to _UAPI_CAN_DIAG_H_
  (Oliver Hartkopp)
- handled J1939 addressing in sockaddr_can
  (Oliver Hartkopp)
- Link to RFC: https://lore.kernel.org/linux-can/20260402-feat-can-diag-v1-0-245b56434c1b@redhat.com/

---
Davide Caratti (1):
      af_can: ensure sk_protocol is always set on socket creation

Filippo Storniolo (2):
      af_can: store socket pointers in struct netns_can
      can: add can diag interface

 MAINTAINERS                   |   1 +
 include/linux/can/core.h      |  11 +++
 include/net/netns/can.h       |   6 ++
 include/uapi/linux/can/diag.h |  50 +++++++++++
 net/can/Kconfig               |  10 +++
 net/can/Makefile              |   3 +
 net/can/af_can.c              |  51 +++++++++++
 net/can/bcm.c                 |   2 +
 net/can/diag.c                | 203 ++++++++++++++++++++++++++++++++++++++++++
 net/can/isotp.c               |   2 +
 net/can/j1939/socket.c        |   3 +-
 net/can/raw.c                 |   2 +
 12 files changed, 343 insertions(+), 1 deletion(-)
---
base-commit: 6ebcf5074cff0402730c6981d2397139fee6322d
change-id: 20260529-feat-can-diag-d7acbf5e22c2

Best regards,
-- 
Filippo Storniolo <fstornio@redhat.com>

[PATCH can-next v3 1/3] af_can: ensure sk_protocol is always set on socket creation

[Filippo Storniolo]

From: Davide Caratti <dcaratti@redhat.com>

Currently, only j1939 assigns a value to 'sk_protocol'. As a prerequisite
for the implementation of CAN sockets diagnostics, AF_CAN sockets need an
easy way to determine which protocol is on top of an existing socket.

POC test using can-tests:

 | # perf probe -m can_j1939 --add "j1939_sk_recvmsg sock->sk->sk_protocol"
 | # perf record -e probe:j1939_sk_recvmsg -aR -- ./j1939/tst-j1939-ac
 | [...]
 | # perf script
 | tst-j1939-ac  5807 [002] 322767.312599: probe:j1939_sk_recvmsg: (ffffffffc0b29a14) sk_protocol=0x7
 |  ^^^ 0x7, that's CAN_J1939

 | # perf probe -m can_raw --add "raw_recvmsg sock->sk->sk_protocol"
 | # perf record -e probe:raw_recvmsg -aR ./netlayer/tst-rcv-own-msgs vcan0
 | # perf script
 | [...]
 | tst-rcv-own-msg  5816 [001] 323173.651122: probe:raw_recvmsg: (ffffffffc0b20154) sk_protocol=0x1
 |  ^^^ 0x1, that's CAN_RAW. It was 0x0 on unpatched kernel

Storing the "protocol" value in can_create() fixes the problem. This also
fixes AF_CAN support for the following system call:

 | getsockopt(..., SOL_SOCKET, SO_PROTOCOL, &proto, sizeof(proto))

that was assigning 0 to 'proto' since the earliest kernel versions.

Fixes: 0d66548a10cb ("[CAN]: Add PF_CAN core module")
Signed-off-by: Davide Caratti <dcaratti@redhat.com>
---
 net/can/af_can.c       | 1 +
 net/can/j1939/socket.c | 1 -
 2 files changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/can/af_can.c b/net/can/af_can.c
index 7bc86b176b4d..65af25946985 100644
--- a/net/can/af_can.c
+++ b/net/can/af_can.c
@@ -162,6 +162,7 @@ static int can_create(struct net *net, struct socket *sock, int protocol,
 	}
 
 	sock_init_data(sock, sk);
+	sk->sk_protocol = protocol;
 	sk->sk_destruct = can_sock_destruct;
 
 	if (sk->sk_prot->init)
diff --git a/net/can/j1939/socket.c b/net/can/j1939/socket.c
index 50a598ef5fd4..ccd43ff5519c 100644
--- a/net/can/j1939/socket.c
+++ b/net/can/j1939/socket.c
@@ -420,7 +420,6 @@ static int j1939_sk_init(struct sock *sk)
 	/* j1939_sk_sock_destruct() depends on SOCK_RCU_FREE flag */
 	sock_set_flag(sk, SOCK_RCU_FREE);
 	sk->sk_destruct = j1939_sk_sock_destruct;
-	sk->sk_protocol = CAN_J1939;
 
 	return 0;
 }

-- 
2.55.0

[PATCH can-next v3 2/3] af_can: store socket pointers in struct netns_can

[Filippo Storniolo]

AF_CAN sockets need to be stored in the netns_can structure
in order to be retrieved by the CAN diagnostic module when
a netlink request message is issued by the userspace.

On socket creation (`can_create()`), add the pointer to the
new socket to `netns_can::sk_list`. During socket release
(`isotp_release()`, `raw_release()`, `j1939_release()`,
`bcm_release()`), remove the corresponding pointer from
this list.

Since this is a prerequisite of the CAN diagnostic module,
deletes and insert operations are conditioned by
IS_ENABLED(CONFIG_CAN_DIAG).

Signed-off-by: Filippo Storniolo <fstornio@redhat.com>
---
 include/linux/can/core.h | 11 +++++++++++
 include/net/netns/can.h  |  6 ++++++
 net/can/af_can.c         | 50 ++++++++++++++++++++++++++++++++++++++++++++++++
 net/can/bcm.c            |  2 ++
 net/can/isotp.c          |  2 ++
 net/can/j1939/socket.c   |  2 ++
 net/can/raw.c            |  2 ++
 7 files changed, 75 insertions(+)

diff --git a/include/linux/can/core.h b/include/linux/can/core.h
index 3287232e3cad..75d9139f33fb 100644
--- a/include/linux/can/core.h
+++ b/include/linux/can/core.h
@@ -61,4 +61,15 @@ extern int can_send(struct sk_buff *skb, int loop);
 void can_set_skb_uid(struct sk_buff *skb);
 void can_sock_destruct(struct sock *sk);
 
+/* function prototypes for the CAN diag module */
+#if IS_ENABLED(CONFIG_CAN_DIAG)
+void lock_can_diag_mutex(struct net *net);
+void unlock_can_diag_mutex(struct net *net);
+void can_add_sock_sklist(struct sock *sk);
+void can_remove_sock_sklist(struct sock *sk);
+#else
+static inline void can_add_sock_sklist(struct sock *sk) {};
+static inline void can_remove_sock_sklist(struct sock *sk) {};
+#endif
+
 #endif /* !_CAN_CORE_H */
diff --git a/include/net/netns/can.h b/include/net/netns/can.h
index 48b79f7e6236..d60273d8a95d 100644
--- a/include/net/netns/can.h
+++ b/include/net/netns/can.h
@@ -36,6 +36,12 @@ struct netns_can {
 
 	/* CAN GW per-net gateway jobs */
 	struct hlist_head cgw_list;
+
+#if IS_ENABLED(CONFIG_CAN_DIAG)
+	/* CAN diag support */
+	struct mutex sklist_lock;
+	struct hlist_head sklist;
+#endif
 };
 
 #endif /* __NETNS_CAN_H__ */
diff --git a/net/can/af_can.c b/net/can/af_can.c
index 65af25946985..1ea36411f219 100644
--- a/net/can/af_can.c
+++ b/net/can/af_can.c
@@ -111,6 +111,44 @@ static inline void can_put_proto(const struct can_proto *cp)
 	module_put(cp->prot->owner);
 }
 
+#if IS_ENABLED(CONFIG_CAN_DIAG)
+void lock_can_diag_mutex(struct net *net)
+{
+	mutex_lock(&net->can.sklist_lock);
+}
+EXPORT_SYMBOL(lock_can_diag_mutex);
+
+void unlock_can_diag_mutex(struct net *net)
+{
+	mutex_unlock(&net->can.sklist_lock);
+}
+EXPORT_SYMBOL(unlock_can_diag_mutex);
+
+void can_add_sock_sklist(struct sock *sk)
+{
+	struct net *net;
+
+	net = sock_net(sk);
+
+	lock_can_diag_mutex(net);
+	sk_add_node(sk, &net->can.sklist);
+	unlock_can_diag_mutex(net);
+}
+EXPORT_SYMBOL(can_add_sock_sklist);
+
+void can_remove_sock_sklist(struct sock *sk)
+{
+	struct net *net;
+
+	net = sock_net(sk);
+
+	lock_can_diag_mutex(net);
+	sk_del_node_init(sk);
+	unlock_can_diag_mutex(net);
+}
+EXPORT_SYMBOL(can_remove_sock_sklist);
+#endif
+
 static int can_create(struct net *net, struct socket *sock, int protocol,
 		      int kern)
 {
@@ -174,6 +212,8 @@ static int can_create(struct net *net, struct socket *sock, int protocol,
 		sock_put(sk);
 		sock->sk = NULL;
 	} else {
+		can_add_sock_sklist(sk);
+
 		sock_prot_inuse_add(net, sk->sk_prot, 1);
 	}
 
@@ -799,6 +839,12 @@ EXPORT_SYMBOL(can_proto_unregister);
 static int can_pernet_init(struct net *net)
 {
 	spin_lock_init(&net->can.rcvlists_lock);
+
+#if IS_ENABLED(CONFIG_CAN_DIAG)
+	mutex_init(&net->can.sklist_lock);
+	INIT_HLIST_HEAD(&net->can.sklist);
+#endif
+
 	net->can.rx_alldev_list = kzalloc_obj(*net->can.rx_alldev_list);
 	if (!net->can.rx_alldev_list)
 		goto out;
@@ -842,6 +888,10 @@ static void can_pernet_exit(struct net *net)
 	kfree(net->can.rx_alldev_list);
 	kfree(net->can.pkg_stats);
 	kfree(net->can.rcv_lists_stats);
+
+#if IS_ENABLED(CONFIG_CAN_DIAG)
+	WARN_ON_ONCE(!hlist_empty(&net->can.sklist));
+#endif
 }
 
 /* af_can module init/exit functions */
diff --git a/net/can/bcm.c b/net/can/bcm.c
index 3d637a1e0ac1..a90b7aea2869 100644
--- a/net/can/bcm.c
+++ b/net/can/bcm.c
@@ -1921,6 +1921,8 @@ static int bcm_release(struct socket *sock)
 	if (!sk)
 		return 0;
 
+	can_remove_sock_sklist(sk);
+
 	net = sock_net(sk);
 	bo = bcm_sk(sk);
 
diff --git a/net/can/isotp.c b/net/can/isotp.c
index 155530aedce2..25098c5546d2 100644
--- a/net/can/isotp.c
+++ b/net/can/isotp.c
@@ -1455,6 +1455,8 @@ static int isotp_release(struct socket *sock)
 	so = isotp_sk(sk);
 	net = sock_net(sk);
 
+	can_remove_sock_sklist(sk);
+
 	/* best-effort: wait for a running pdu to finish, but don't block on
 	 * it forever - give up after the first signal
 	 */
diff --git a/net/can/j1939/socket.c b/net/can/j1939/socket.c
index ccd43ff5519c..cbfd0b888768 100644
--- a/net/can/j1939/socket.c
+++ b/net/can/j1939/socket.c
@@ -641,6 +641,8 @@ static int j1939_sk_release(struct socket *sock)
 	if (!sk)
 		return 0;
 
+	can_remove_sock_sklist(sk);
+
 	lock_sock(sk);
 	jsk = j1939_sk(sk);
 
diff --git a/net/can/raw.c b/net/can/raw.c
index 82d9c0499c95..7784b8fd8d19 100644
--- a/net/can/raw.c
+++ b/net/can/raw.c
@@ -418,6 +418,8 @@ static int raw_release(struct socket *sock)
 	ro = raw_sk(sk);
 	net = sock_net(sk);
 
+	can_remove_sock_sklist(sk);
+
 	spin_lock(&raw_notifier_lock);
 	while (raw_busy_notifier == ro) {
 		spin_unlock(&raw_notifier_lock);

-- 
2.55.0

[PATCH can-next v3 3/3] can: add can diag interface

[Filippo Storniolo]

Add the can_diag interface for querying sockets from userspace.
ss(8) tool can use this interface to list open sockets.

The userspace ABI is defined in <linux/can/diag.h> and includes
netlink request and response structs.  The request queries open
can sockets and the response contains socket information fields
including the interface index for bound sockets, inode number,
transport protocol etc.

Support can be added later by extending can_diag_dump().

Suggested-by: Davide Caratti <dcaratti@redhat.com>
Signed-off-by: Filippo Storniolo <fstornio@redhat.com>
---
 MAINTAINERS                   |   1 +
 include/uapi/linux/can/diag.h |  50 +++++++++++
 net/can/Kconfig               |  10 +++
 net/can/Makefile              |   3 +
 net/can/diag.c                | 203 ++++++++++++++++++++++++++++++++++++++++++
 5 files changed, 267 insertions(+)

diff --git a/MAINTAINERS b/MAINTAINERS
index b23fb6f2f4ef..c718d7477fa7 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -5859,6 +5859,7 @@ F:	include/net/can.h
 F:	include/net/netns/can.h
 F:	include/uapi/linux/can.h
 F:	include/uapi/linux/can/bcm.h
+F:	include/uapi/linux/can/diag.h
 F:	include/uapi/linux/can/gw.h
 F:	include/uapi/linux/can/isotp.h
 F:	include/uapi/linux/can/raw.h
diff --git a/include/uapi/linux/can/diag.h b/include/uapi/linux/can/diag.h
new file mode 100644
index 000000000000..f22103e7bf90
--- /dev/null
+++ b/include/uapi/linux/can/diag.h
@@ -0,0 +1,50 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+
+#ifndef _UAPI_CAN_DIAG_H_
+#define _UAPI_CAN_DIAG_H_
+
+#include <linux/types.h>
+#include <linux/can.h>
+#include <linux/const.h>
+
+/* Request */
+struct can_diag_req {
+	__u8	sdiag_family;	/* must be AF_CAN */
+	__u8	pad;
+	__u16	sdiag_protocol; /* for future filtering of transport protocols */
+	__u32	cdiag_states;
+	__u32	cdiag_ino;
+	__u32	cdiag_show;
+	__u32	cdiag_cookie[2];
+};
+
+#define CDIAG_SHOW_UID		_BITUL(0) /* show socket's UID */
+
+enum {
+	CAN_DIAG_UNSPEC,
+	CAN_DIAG_UID,
+	CAN_DIAG_ISOTP_TX_ID,
+	CAN_DIAG_ISOTP_RX_ID,
+	CAN_DIAG_J1939_NAME,
+	CAN_DIAG_J1939_PGN,
+	CAN_DIAG_J1939_ADDR,
+
+	__CAN_DIAG_MAX,
+};
+
+#define CAN_DIAG_MAX (__CAN_DIAG_MAX - 1)
+
+/* Response */
+struct can_diag_msg {
+	__u8	cdiag_family;	/* AF_CAN */
+	__u8	cdiag_state;
+	__u16	cdiag_protocol;
+	__u16	cdiag_type;
+	__u16	pad16;
+	__u32	cdiag_cookie[2];
+	__s32	cdiag_ifindex;
+	__u32	pad32;
+	__u64	cdiag_ino;
+};
+
+#endif /* _UAPI_CAN_DIAG_H_ */
diff --git a/net/can/Kconfig b/net/can/Kconfig
index abbb4be7ad21..bbab2c70326b 100644
--- a/net/can/Kconfig
+++ b/net/can/Kconfig
@@ -70,4 +70,14 @@ config CAN_ISOTP
 	  as needed e.g. for vehicle diagnosis (UDS, ISO 14229) or IP-over-CAN
 	  traffic.
 
+config CAN_DIAG
+	tristate "CAN socket monitoring interface"
+	depends on CAN
+	default m
+	help
+	  Support for CAN socket monitoring interface used by the ss tool.
+	  If unsure, say M.
+
+	  Enable this module so userspace applications can query open sockets.
+
 endif
diff --git a/net/can/Makefile b/net/can/Makefile
index 58f2c31c1ef3..c0ddeb9a012c 100644
--- a/net/can/Makefile
+++ b/net/can/Makefile
@@ -20,3 +20,6 @@ obj-$(CONFIG_CAN_J1939)	+= j1939/
 
 obj-$(CONFIG_CAN_ISOTP)	+= can-isotp.o
 can-isotp-y		:= isotp.o
+
+obj-$(CONFIG_CAN_DIAG) += can-diag.o
+can-diag-y		:= diag.o
diff --git a/net/can/diag.c b/net/can/diag.c
new file mode 100644
index 000000000000..647a94636a54
--- /dev/null
+++ b/net/can/diag.c
@@ -0,0 +1,203 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ *
+ * Copyright (C) 2026 Red Hat
+ * Author: Filippo Storniolo <fstornio@redhat.com>
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/net.h>
+#include <net/netlink.h>
+#include <linux/sock_diag.h>
+#include <linux/can.h>
+#include <linux/can/diag.h>
+#include <net/net_namespace.h>
+#include <net/sock.h>
+#include <linux/netdevice.h>
+#include <linux/user_namespace.h>
+#include <linux/can/core.h>
+
+static int sk_diag_dump_uid(struct sock *sk, struct sk_buff *skb,
+			    struct user_namespace *user_ns)
+{
+	uid_t uid = from_kuid_munged(user_ns, sk_uid(sk));
+
+	return nla_put(skb, CAN_DIAG_UID, sizeof(uid_t), &uid);
+}
+
+static int sk_diag_fill(struct sock *sk, struct sk_buff *skb,
+			struct can_diag_req *req, /* will be used for filtering */
+			struct user_namespace *user_ns,
+			u32 portid, u32 seq, u32 flags, u64 sk_ino)
+{
+	struct sockaddr_can can_addr;
+	struct can_diag_msg *rep;
+	struct nlmsghdr *nlh;
+	int err;
+
+	nlh = nlmsg_put(skb, portid, seq, SOCK_DIAG_BY_FAMILY, sizeof(*rep), flags);
+	if (!nlh)
+		return -EMSGSIZE;
+
+	rep = nlmsg_data(nlh);
+	memset(rep, 0, sizeof(struct can_diag_msg));
+
+	rep->cdiag_family = AF_CAN;
+	rep->cdiag_type = sk->sk_type;
+	rep->cdiag_ino = sk_ino;
+	rep->cdiag_protocol = sk->sk_protocol;
+	rep->cdiag_state = READ_ONCE(sk->sk_state);
+	sock_diag_save_cookie(sk, rep->cdiag_cookie);
+
+	if ((req->cdiag_show & CDIAG_SHOW_UID)) {
+		err = sk_diag_dump_uid(sk, skb, user_ns);
+		if (err < 0)
+			goto cancel_nlmsg_err;
+	}
+
+	memset(&can_addr, 0, sizeof(can_addr));
+
+	err = kernel_getsockname(sk->sk_socket, (struct sockaddr *)&can_addr);
+	if (err < 0) {
+		/* Some protocols (e.g. CAN_BCM) do not implement kernel_getsockname().
+		 * No error returned because the netlink message is still valid.
+		 */
+		if (err == -EOPNOTSUPP)
+			goto exit_no_err;
+
+		goto cancel_nlmsg_err;
+	}
+
+	rep->cdiag_ifindex = can_addr.can_ifindex;
+
+	switch (sk->sk_protocol) {
+	case CAN_ISOTP:
+	{
+		canid_t tx_id;
+		canid_t rx_id;
+
+		tx_id = can_addr.can_addr.tp.tx_id;
+		rx_id = can_addr.can_addr.tp.rx_id;
+
+		err = nla_put(skb, CAN_DIAG_ISOTP_TX_ID, sizeof(canid_t), &tx_id);
+		if (err < 0)
+			goto cancel_nlmsg_err;
+
+		err = nla_put(skb, CAN_DIAG_ISOTP_RX_ID, sizeof(canid_t), &rx_id);
+		if (err < 0)
+			goto cancel_nlmsg_err;
+	}
+		break;
+	case CAN_J1939:
+	{
+		__u64	j1939_name;
+		__u32	j1939_pgn;
+		__u8	j1939_addr;
+
+		j1939_name = can_addr.can_addr.j1939.name;
+		j1939_pgn = can_addr.can_addr.j1939.pgn;
+		j1939_addr = can_addr.can_addr.j1939.addr;
+
+		err = nla_put(skb, CAN_DIAG_J1939_NAME, sizeof(j1939_name), &j1939_name);
+		if (err < 0)
+			goto cancel_nlmsg_err;
+
+		err = nla_put(skb, CAN_DIAG_J1939_PGN, sizeof(j1939_pgn), &j1939_pgn);
+		if (err < 0)
+			goto cancel_nlmsg_err;
+
+		err = nla_put(skb, CAN_DIAG_J1939_ADDR, sizeof(j1939_addr), &j1939_addr);
+		if (err < 0)
+			goto cancel_nlmsg_err;
+	}
+		break;
+	default:
+		break;
+	}
+
+exit_no_err:
+	nlmsg_end(skb, nlh);
+	return 0;
+
+cancel_nlmsg_err:
+	nlmsg_cancel(skb, nlh);
+	return err;
+}
+
+static int can_diag_dump(struct sk_buff *skb, struct netlink_callback *cb)
+{
+	int num = 0, s_num = cb->args[0];
+	struct can_diag_req *req;
+	struct net *net;
+	struct sock *sk;
+
+	net = sock_net(skb->sk);
+	req = nlmsg_data(cb->nlh);
+
+	lock_can_diag_mutex(net);
+	sk_for_each(sk, &net->can.sklist) {
+		if (num < s_num)
+			goto next;
+
+		if (sk_diag_fill(sk, skb, req,
+				 sk_user_ns(NETLINK_CB(cb->skb).sk),
+				 NETLINK_CB(cb->skb).portid,
+				 cb->nlh->nlmsg_seq, NLM_F_MULTI,
+				 sock_i_ino(sk)) < 0)
+			goto done;
+next:
+		num++;
+	}
+done:
+	unlock_can_diag_mutex(net);
+	cb->args[0] = num;
+
+	return skb->len;
+}
+
+static int can_diag_handler_dump(struct sk_buff *skb, struct nlmsghdr *h)
+{
+	int hdrlen = sizeof(struct can_diag_req);
+	struct net *net = sock_net(skb->sk);
+	struct can_diag_req *req;
+
+	if (nlmsg_len(h) < hdrlen)
+		return -EINVAL;
+
+	req = nlmsg_data(h);
+	if (req->sdiag_protocol)
+		return -EINVAL;
+
+	if (h->nlmsg_flags & NLM_F_DUMP) {
+		struct netlink_dump_control c = {
+			.dump = can_diag_dump
+		};
+		return netlink_dump_start(net->diag_nlsk, skb, h, &c);
+	}
+
+	return -EOPNOTSUPP;
+}
+
+static const struct sock_diag_handler can_diag_handler = {
+	.owner = THIS_MODULE,
+	.family = AF_CAN,
+	.dump = can_diag_handler_dump,
+};
+
+static int __init can_diag_init(void)
+{
+	pr_info("can: diagnostic module\n");
+	return sock_diag_register(&can_diag_handler);
+}
+
+static void __exit can_diag_exit(void)
+{
+	sock_diag_unregister(&can_diag_handler);
+}
+
+module_init(can_diag_init);
+module_exit(can_diag_exit);
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("CAN socket monitoring via SOCK_DIAG");
+MODULE_ALIAS_NET_PF_PROTO_TYPE(PF_NETLINK, NETLINK_SOCK_DIAG, AF_CAN);

-- 
2.55.0

Re: [PATCH can-next v3 3/3] can: add can diag interface

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] Index-based resumption in can_diag_dump() causes skipped or repeated sockets without notifying userspace via NLM_F_DUMP_INTR.
--

commit 8ae9bc3a24d9d75317a64a778b0ca0dc88c6a32a
Author: Filippo Storniolo <fstornio@redhat.com>

can: add can diag interface
    
Add the can_diag interface for querying sockets from userspace. The ss(8)
tool can use this interface to list open sockets. The userspace ABI includes
netlink request and response structs with socket information fields.

> diff --git a/net/can/diag.c b/net/can/diag.c
> new file mode 100644
> index 0000000000000..647a94636a548
> --- /dev/null
> +++ b/net/can/diag.c

[ ... ]

> +static int can_diag_dump(struct sk_buff *skb, struct netlink_callback *cb)
> +{
> +	int num = 0, s_num = cb->args[0];
> +	struct can_diag_req *req;
> +	struct net *net;
> +	struct sock *sk;
> +
> +	net = sock_net(skb->sk);
> +	req = nlmsg_data(cb->nlh);
> +
> +	lock_can_diag_mutex(net);
> +	sk_for_each(sk, &net->can.sklist) {
> +		if (num < s_num)
> +			goto next;
> +
> +		if (sk_diag_fill(sk, skb, req,

[Severity: Medium]
Will this simple index-based resumption (num < s_num) cause skipped or
repeated sockets without notifying userspace if the list is modified between
dump iterations?

A netlink dump of CAN sockets can require multiple messages, forcing
can_diag_dump() to return and resume later. If a concurrent thread creates
or destroys a CAN socket, altering the layout of net->can.sklist while the
mutex is dropped, iteration by index becomes inaccurate.

According to the Netlink uAPI guidelines, if iteration during a dump may skip
or repeat objects, NLM_F_DUMP_INTR must be set on the affected messages. This
is normally implemented by maintaining a generation counter and recording it
in cb->seq to detect list modifications.

> +				 sk_user_ns(NETLINK_CB(cb->skb).sk),
> +				 NETLINK_CB(cb->skb).portid,
> +				 cb->nlh->nlmsg_seq, NLM_F_MULTI,
> +				 sock_i_ino(sk)) < 0)
> +			goto done;
> +next:
> +		num++;
> +	}
> +done:
> +	unlock_can_diag_mutex(net);
> +	cb->args[0] = num;
> +
> +	return skb->len;
> +}

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260904-feat-can-diag-v3-0-bdcebf07b373@redhat.com?part=3