af_unix: Fix wrong ioctl(SIOCATMARK) when consumed OOB skb is at the head.

Even if OOB data is recv()ed, ioctl(SIOCATMARK) must return 1 when the
OOB skb is at the head of the receive queue and no new OOB data is queued.

Without fix:

# RUN msg_oob.no_peek.oob ...
# msg_oob.c:305:oob:Expected answ[0] (0) == oob_head (1)
# oob: Test terminated by assertion
# FAIL msg_oob.no_peek.oob
not ok 2 msg_oob.no_peek.oob

With fix:

# RUN msg_oob.no_peek.oob ...
# OK msg_oob.no_peek.oob
ok 2 msg_oob.no_peek.oob

Fixes: 314001f0bf92 ("af_unix: Add OOB support")
Signed-off-by: Kuniyuki Iwashima <[e-mail]>
Signed-off-by: Paolo Abeni <[e-mail]>

net/unix/af_unix.c

···
 #if IS_ENABLED(CONFIG_AF_UNIX_OOB)
 	case SIOCATMARK:
 		{
+			struct unix_sock *u = unix_sk(sk);
 			struct sk_buff *skb;
 			int answ = 0;
 
+			mutex_lock(&u->iolock);
+
 			skb = skb_peek(&sk->sk_receive_queue);
-			if (skb && skb == READ_ONCE(unix_sk(sk)->oob_skb))
-				answ = 1;
+			if (skb) {
+				struct sk_buff *oob_skb = READ_ONCE(u->oob_skb);
+
+				if (skb == oob_skb ||
+				    (!oob_skb && !unix_skb_len(skb)))
+					answ = 1;
+			}
+
+			mutex_unlock(&u->iolock);
+
 			err = put_user(answ, (int __user *)arg);
 		}
 		break;

tools/testing/selftests/net/af_unix/msg_oob.c

···
 	}
 }
 
+static void __siocatmarkpair(struct __test_metadata *_metadata,
+			     FIXTURE_DATA(msg_oob) *self,
+			     bool oob_head)
+{
+	int answ[2] = {};
+	int i;
+
+	for (i = 0; i < 2; i++) {
+		int ret;
+
+		ret = ioctl(self->fd[i * 2 + 1], SIOCATMARK, &answ[i]);
+		ASSERT_EQ(ret, 0);
+	}
+
+	ASSERT_EQ(answ[0], oob_head);
+
+	if (self->tcp_compliant)
+		ASSERT_EQ(answ[0], answ[1]);
+}
+
 #define sendpair(buf, len, flags)					\
 	__sendpair(_metadata, self, buf, len, flags)
 
···
 
 #define epollpair(oob_remaining)					\
 	__epollpair(_metadata, self, oob_remaining)
+
+#define siocatmarkpair(oob_head)					\
+	__siocatmarkpair(_metadata, self, oob_head)
 
 #define setinlinepair()							\
 	__setinlinepair(_metadata, self)
···
 {
 	sendpair("x", 1, MSG_OOB);
 	epollpair(true);
+	siocatmarkpair(true);
 
 	recvpair("x", 1, 1, MSG_OOB);
 	epollpair(false);
+	siocatmarkpair(true);
 }
 
 TEST_F(msg_oob, oob_drop)
···
 	epollpair(false);
 }
 
+TEST_F(msg_oob, ex_oob_siocatmark)
+{
+	sendpair("hello", 5, MSG_OOB);
+	epollpair(true);
+	siocatmarkpair(false);
+
+	recvpair("o", 1, 1, MSG_OOB);
+	epollpair(false);
+	siocatmarkpair(false);
+
+	sendpair("world", 5, MSG_OOB);
+	epollpair(true);
+	siocatmarkpair(false);
+
+	recvpair("hell", 4, 4, 0);		/* Intentionally stop at ex-OOB. */
+	epollpair(true);
+	siocatmarkpair(false);
+}
+
 TEST_F(msg_oob, inline_oob)
 {
 	setinlinepair();
 
 	sendpair("x", 1, MSG_OOB);
 	epollpair(true);
+	siocatmarkpair(true);
 
 	recvpair("", -EINVAL, 1, MSG_OOB);
 	epollpair(true);
+	siocatmarkpair(true);
 
 	recvpair("x", 1, 1, 0);
 	epollpair(false);
+	siocatmarkpair(false);
 }
 
 TEST_F(msg_oob, inline_oob_break)
···
 		recvpair("y", 1, 1, 0);		/* TCP returns -EAGAIN. */
 		epollpair(false);
 	}
+}
+
+TEST_F(msg_oob, inline_ex_oob_siocatmark)
+{
+	sendpair("hello", 5, MSG_OOB);
+	epollpair(true);
+	siocatmarkpair(false);
+
+	recvpair("o", 1, 1, MSG_OOB);
+	epollpair(false);
+	siocatmarkpair(false);
+
+	setinlinepair();
+
+	sendpair("world", 5, MSG_OOB);
+	epollpair(true);
+	siocatmarkpair(false);
+
+	recvpair("hell", 4, 4, 0);		/* Intentionally stop at ex-OOB. */
+	epollpair(true);
+	siocatmarkpair(false);
 }
 
 TEST_HARNESS_MAIN