af_unix: Reject SIOCATMARK on non-stream sockets

SIOCATMARK reports whether the receive queue is at the urgent mark for
MSG_OOB.

In AF_UNIX, MSG_OOB is supported only for SOCK_STREAM sockets.
SOCK_DGRAM and SOCK_SEQPACKET reject MSG_OOB in sendmsg() and recvmsg(),
so they should not support SIOCATMARK either.

Return -EOPNOTSUPP for non-stream sockets before checking the receive
queue.

Fixes: 314001f ("af_unix: Add OOB support")
Cc: stable@kernel.org
Reported-by: Yuan Tan <yuantan098@gmail.com>
Reported-by: Yifan Wu <yifanwucs@gmail.com>
Reported-by: Juefei Pu <tomapufckgml@gmail.com>
Reported-by: Xin Liu <bird@lzu.edu.cn>
Suggested-by: Kuniyuki Iwashima <kuniyu@google.com>
Signed-off-by: Jiexun Wang <wangjiexun2025@gmail.com>
Signed-off-by: Ren Wei <n05ec@lzu.edu.cn>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/20260506140825.2987635-1-n05ec@lzu.edu.cn
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: JiexunWang

net/unix/af_unix.c

@@ -3323,6 +3323,9 @@ static int unix_ioctl(struct socket *sock, unsigned int cmd, unsigned long arg)
 			struct sk_buff *skb;
 			int answ = 0;
 
+			if (sk->sk_type != SOCK_STREAM)
+				return -EOPNOTSUPP;
+
 			mutex_lock(&u->iolock);
 
 			skb = skb_peek(&sk->sk_receive_queue);