af_unix: Stop recv(MSG_PEEK) at consumed OOB skb.

[ Upstream commit b94038d841a91d0e3f59cfe4d073e210910366ee ]

After consuming OOB data, recv() reading the preceding data must break at
the OOB skb regardless of MSG_PEEK.

Currently, MSG_PEEK does not stop recv() for AF_UNIX, and the behaviour is
not compliant with TCP.

  >>> from socket import *
  >>> c1, c2 = socketpair(AF_UNIX)
  >>> c1.send(b'hello', MSG_OOB)
  5
  >>> c1.send(b'world')
  5
  >>> c2.recv(1, MSG_OOB)
  b'o'
  >>> c2.recv(9, MSG_PEEK)  # This should return b'hell'
  b'hellworld'              # even with enough buffer.

Let's fix it by returning NULL for consumed skb and unlinking it only if
MSG_PEEK is not specified.

This patch also adds test cases that add recv(MSG_PEEK) before each recv().

Without fix:

  #  RUN           msg_oob.peek.oob_ahead_break ...
  # msg_oob.c:134:oob_ahead_break:AF_UNIX :hellworld
  # msg_oob.c:135:oob_ahead_break:Expected:hell
  # msg_oob.c:137:oob_ahead_break:Expected ret[0] (9) == expected_len (4)
  # oob_ahead_break: Test terminated by assertion
  #          FAIL  msg_oob.peek.oob_ahead_break
  not ok 13 msg_oob.peek.oob_ahead_break

With fix:

  #  RUN           msg_oob.peek.oob_ahead_break ...
  #            OK  msg_oob.peek.oob_ahead_break
  ok 13 msg_oob.peek.oob_ahead_break

Fixes: 314001f0bf92 ("af_unix: Add OOB support")
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 68a58bc07cf2309aebc181e4b0c344da148313a9..d687670e849907d1030e180d935363d934691ea2 100644 (file)
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -2660,9 +2660,12 @@ static struct sk_buff *manage_oob(struct sk_buff *skb, struct sock *sk,
 {
        struct unix_sock *u = unix_sk(sk);
 
-       if (!unix_skb_len(skb) && !(flags & MSG_PEEK)) {
-               skb_unlink(skb, &sk->sk_receive_queue);
-               consume_skb(skb);
+       if (!unix_skb_len(skb)) {
+               if (!(flags & MSG_PEEK)) {
+                       skb_unlink(skb, &sk->sk_receive_queue);
+                       consume_skb(skb);
+               }
+
                skb = NULL;
        } else {
                struct sk_buff *unlinked_skb = NULL;