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

@@ -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

@@ -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_ */

@@ -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

@@ -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

@@ -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);