sctp: set sk_state back to CLOSED if autobind fails in sctp_listen_start

In sctp_listen_start() invoked by sctp_inet_listen(), it should set the
sk_state back to CLOSED if sctp_autobind() fails due to whatever reason.

Otherwise, next time when calling sctp_inet_listen(), if sctp_sk(sk)->reuse
is already set via setsockopt(SCTP_REUSE_PORT), sctp_sk(sk)->bind_hash will
be dereferenced as sk_state is LISTENING, which causes a crash as bind_hash
is NULL.

  KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
  RIP: 0010:sctp_inet_listen+0x7f0/0xa20 net/sctp/socket.c:8617
  Call Trace:
   <TASK>
   __sys_listen_socket net/socket.c:1883 [inline]
   __sys_listen+0x1b7/0x230 net/socket.c:1894
   __do_sys_listen net/socket.c:1902 [inline]

Fixes: 5e8f3f70 ("sctp: simplify sctp listening code")
Reported-by: syzbot+f4e0f821e3a3b7cee51d@syzkaller.appspotmail.com
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Acked-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Link: https://patch.msgid.link/a93e655b3c153dc8945d7a812e6d8ab0d52b7aa0.1727729391.git.lucien.xin@gmail.comSigned-off-by: Paolo Abeni <pabeni@redhat.com>

net/sctp/socket.c

@@ -8557,8 +8557,10 @@ static int sctp_listen_start(struct sock *sk, int backlog)
 	 */
 	inet_sk_set_state(sk, SCTP_SS_LISTENING);
 	if (!ep->base.bind_addr.port) {
-		if (sctp_autobind(sk))
+		if (sctp_autobind(sk)) {
+			inet_sk_set_state(sk, SCTP_SS_CLOSED);
 			return -EAGAIN;
+		}
 	} else {
 		if (sctp_get_port(sk, inet_sk(sk)->inet_num)) {
 			inet_sk_set_state(sk, SCTP_SS_CLOSED);