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: 314001f0bf ("af_unix: Add OOB support")
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

net/unix/af_unix.c

@@ -3107,12 +3107,23 @@ static int unix_ioctl(struct socket *sock, unsigned int cmd, unsigned long arg)
 #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))
+			if (skb) {
-				answ = 1;
+				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

@@ -288,6 +288,26 @@ static void __setinlinepair(struct __test_metadata *_metadata,
 	}
 }
 
+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)
 
@@ -304,6 +324,9 @@ static void __setinlinepair(struct __test_metadata *_metadata,
 #define epollpair(oob_remaining)					\
 	__epollpair(_metadata, self, oob_remaining)
 
+#define siocatmarkpair(oob_head)					\
+	__siocatmarkpair(_metadata, self, oob_head)
+
 #define setinlinepair()							\
 	__setinlinepair(_metadata, self)
 
@@ -325,9 +348,11 @@ TEST_F(msg_oob, oob)
 {
 	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)
@@ -481,18 +506,40 @@ TEST_F(msg_oob, ex_oob_ahead_break)
 	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)
@@ -591,4 +638,25 @@ TEST_F(msg_oob, inline_ex_oob_drop)
 	}
 }
 
+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