net: Split a __sys_listen helper for io_uring

io_uring holds a reference to the file and maintains a sockaddr_storage
address.  Similarly to what was done to __sys_connect_file, split an
internal helper for __sys_listen in preparation to support an
io_uring listen command.

Reviewed-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Gabriel Krisman Bertazi <krisman@suse.de>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Acked-by: Jakub Kicinski <kuba@kernel.org>
Link: https://lore.kernel.org/r/20240614163047.31581-2-krisman@suse.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>

include/linux/socket.h

@@ -449,6 +449,7 @@ extern int __sys_connect_file(struct file *file, struct sockaddr_storage *addr,
 extern int __sys_connect(int fd, struct sockaddr __user *uservaddr,
 			 int addrlen);
 extern int __sys_listen(int fd, int backlog);
+extern int __sys_listen_socket(struct socket *sock, int backlog);
 extern int __sys_getsockname(int fd, struct sockaddr __user *usockaddr,
 			     int __user *usockaddr_len);
 extern int __sys_getpeername(int fd, struct sockaddr __user *usockaddr,

net/socket.c

@@ -1870,23 +1870,28 @@ SYSCALL_DEFINE3(bind, int, fd, struct sockaddr __user *, umyaddr, int, addrlen)
  *	necessary for a listen, and if that works, we mark the socket as
  *	ready for listening.
  */
+int __sys_listen_socket(struct socket *sock, int backlog)
+{
+	int somaxconn, err;
+
+	somaxconn = READ_ONCE(sock_net(sock->sk)->core.sysctl_somaxconn);
+	if ((unsigned int)backlog > somaxconn)
+		backlog = somaxconn;
+
+	err = security_socket_listen(sock, backlog);
+	if (!err)
+		err = READ_ONCE(sock->ops)->listen(sock, backlog);
+	return err;
+}
 
 int __sys_listen(int fd, int backlog)
 {
 	struct socket *sock;
 	int err, fput_needed;
-	int somaxconn;
 
 	sock = sockfd_lookup_light(fd, &err, &fput_needed);
 	if (sock) {
-		somaxconn = READ_ONCE(sock_net(sock->sk)->core.sysctl_somaxconn);
-		if ((unsigned int)backlog > somaxconn)
-			backlog = somaxconn;
-
-		err = security_socket_listen(sock, backlog);
-		if (!err)
-			err = READ_ONCE(sock->ops)->listen(sock, backlog);
-
+		err = __sys_listen_socket(sock, backlog);
 		fput_light(sock->file, fput_needed);
 	}
 	return err;