can: raw: add locking for raw flags bitfield

With commit 890e519 ("can: raw: use bitfields to store flags in
struct raw_sock") the formerly separate integer values have been integrated
into a single bitfield. This led to a read-modify-write operation when
changing a flag in raw_setsockopt() which now needs a locking to prevent
concurrent access.

Instead of adding a lock/unlock hell in each of the flag manipulations this
patch introduces a wrapper for a new raw_setsockopt_locked() function
analogue to the isotp_setsockopt[_locked]() approach in net/can/isotp.c

Fixes: 890e519 ("can: raw: use bitfields to store flags in struct raw_sock")
Reported-by: Eulgyu Kim <eulgyukim@snu.ac.kr>
Closes: https://lore.kernel.org/linux-can/20260503112200.22727-1-eulgyukim@snu.ac.kr/
Tested-by: Eulgyu Kim <eulgyukim@snu.ac.kr>
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
Reviewed-by: Vincent Mailhol <mailhol@kernel.org>
Tested-by: Vincent Mailhol <mailhol@kernel.org>
Link: https://patch.msgid.link/20260504111928.41856-1-socketcan@hartkopp.net
[mkl: use Closes tag instead of Link]
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

Author: hartkopp

net/can/raw.c

@@ -562,8 +562,8 @@ static int raw_getname(struct socket *sock, struct sockaddr *uaddr,
 	return RAW_MIN_NAMELEN;
 }
 
-static int raw_setsockopt(struct socket *sock, int level, int optname,
-			  sockptr_t optval, unsigned int optlen)
+static int raw_setsockopt_locked(struct socket *sock, int optname,
+				 sockptr_t optval, unsigned int optlen)
 {
 	struct sock *sk = sock->sk;
 	struct raw_sock *ro = raw_sk(sk);
@@ -575,9 +575,6 @@ static int raw_setsockopt(struct socket *sock, int level, int optname,
 	int flag;
 	int err = 0;
 
-	if (level != SOL_CAN_RAW)
-		return -EINVAL;
-
 	switch (optname) {
 	case CAN_RAW_FILTER:
 		if (optlen % sizeof(struct can_filter) != 0)
@@ -598,17 +595,11 @@ static int raw_setsockopt(struct socket *sock, int level, int optname,
 				return -EFAULT;
 		}
 
-		rtnl_lock();
-		lock_sock(sk);
-
 		dev = ro->dev;
-		if (ro->bound && dev) {
-			if (dev->reg_state != NETREG_REGISTERED) {
-				if (count > 1)
-					kfree(filter);
-				err = -ENODEV;
-				goto out_fil;
-			}
+		if (ro->bound && dev && dev->reg_state != NETREG_REGISTERED) {
+			if (count > 1)
+				kfree(filter);
+			return -ENODEV;
 		}
 
 		if (ro->bound) {
@@ -622,7 +613,7 @@ static int raw_setsockopt(struct socket *sock, int level, int optname,
 			if (err) {
 				if (count > 1)
 					kfree(filter);
-				goto out_fil;
+				return err;
 			}
 
 			/* remove old filter registrations */
@@ -642,11 +633,6 @@ static int raw_setsockopt(struct socket *sock, int level, int optname,
 		}
 		ro->filter = filter;
 		ro->count  = count;
-
- out_fil:
-		release_sock(sk);
-		rtnl_unlock();
-
 		break;
 
 	case CAN_RAW_ERR_FILTER:
@@ -658,16 +644,9 @@ static int raw_setsockopt(struct socket *sock, int level, int optname,
 
 		err_mask &= CAN_ERR_MASK;
 
-		rtnl_lock();
-		lock_sock(sk);
-
 		dev = ro->dev;
-		if (ro->bound && dev) {
-			if (dev->reg_state != NETREG_REGISTERED) {
-				err = -ENODEV;
-				goto out_err;
-			}
-		}
+		if (ro->bound && dev && dev->reg_state != NETREG_REGISTERED)
+			return -ENODEV;
 
 		/* remove current error mask */
 		if (ro->bound) {
@@ -676,7 +655,7 @@ static int raw_setsockopt(struct socket *sock, int level, int optname,
 						   err_mask);
 
 			if (err)
-				goto out_err;
+				return err;
 
 			/* remove old err_mask registration */
 			raw_disable_errfilter(sock_net(sk), dev, sk,
@@ -685,11 +664,6 @@ static int raw_setsockopt(struct socket *sock, int level, int optname,
 
 		/* link new err_mask to the socket */
 		ro->err_mask = err_mask;
-
- out_err:
-		release_sock(sk);
-		rtnl_unlock();
-
 		break;
 
 	case CAN_RAW_LOOPBACK:
@@ -769,6 +743,26 @@ static int raw_setsockopt(struct socket *sock, int level, int optname,
 	return err;
 }
 
+static int raw_setsockopt(struct socket *sock, int level, int optname,
+			  sockptr_t optval, unsigned int optlen)
+{
+	struct sock *sk = sock->sk;
+	int err;
+
+	if (level != SOL_CAN_RAW)
+		return -EINVAL;
+
+	rtnl_lock();
+	lock_sock(sk);
+
+	err = raw_setsockopt_locked(sock, optname, optval, optlen);
+
+	release_sock(sk);
+	rtnl_unlock();
+
+	return err;
+}
+
 static int raw_getsockopt(struct socket *sock, int level, int optname,
 			  sockopt_t *opt)
 {