net: rose: lock the socket in rose_bind()

syzbot reported a soft lockup in rose_loopback_timer(),
with a repro calling bind() from multiple threads.

rose_bind() must lock the socket to avoid this issue.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Reported-by: syzbot+7ff41b5215f0c534534e@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/netdev/67a0f78d.050a0220.d7c5a.00a0.GAE@google.com/T/#u
Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Paolo Abeni <pabeni@redhat.com>
Link: https://patch.msgid.link/20250203170838.3521361-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: edumazet

net/rose/af_rose.c

@@ -701,11 +701,9 @@ static int rose_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len)
 	struct net_device *dev;
 	ax25_address *source;
 	ax25_uid_assoc *user;
+	int err = -EINVAL;
 	int n;
 
-	if (!sock_flag(sk, SOCK_ZAPPED))
-		return -EINVAL;
-
 	if (addr_len != sizeof(struct sockaddr_rose) && addr_len != sizeof(struct full_sockaddr_rose))
 		return -EINVAL;
 
@@ -718,8 +716,15 @@ static int rose_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len)
 	if ((unsigned int) addr->srose_ndigis > ROSE_MAX_DIGIS)
 		return -EINVAL;
 
-	if ((dev = rose_dev_get(&addr->srose_addr)) == NULL)
-		return -EADDRNOTAVAIL;
+	lock_sock(sk);
+
+	if (!sock_flag(sk, SOCK_ZAPPED))
+		goto out_release;
+
+	err = -EADDRNOTAVAIL;
+	dev = rose_dev_get(&addr->srose_addr);
+	if (!dev)
+		goto out_release;
 
 	source = &addr->srose_call;
 
@@ -730,7 +735,8 @@ static int rose_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len)
 	} else {
 		if (ax25_uid_policy && !capable(CAP_NET_BIND_SERVICE)) {
 			dev_put(dev);
-			return -EACCES;
+			err = -EACCES;
+			goto out_release;
 		}
 		rose->source_call   = *source;
 	}
@@ -753,8 +759,10 @@ static int rose_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len)
 	rose_insert_socket(sk);
 
 	sock_reset_flag(sk, SOCK_ZAPPED);
-
-	return 0;
+	err = 0;
+out_release:
+	release_sock(sk);
+	return err;
 }
 
 static int rose_connect(struct socket *sock, struct sockaddr *uaddr, int addr_len, int flags)