[PATCH v1 net 2/3] af_unix: Return immediately when manage_oob() returns NULL for 0-length buffer.

[Kuniyuki Iwashima <kuniyu@google.com>]

Fahad Alharbi reported that recv(0, MSG_PEEK) triggers busy-wait
in unix_stream_read_generic() if recv() is blocking and the last
skb in the queue is MSG_OOB skb.

In such a situation, TCP returns 0 immediately regardless of
blocking or non-blocking.

Let's follow the behaviour.

Fixes: 314001f0bf92 ("af_unix: Add OOB support")
Reported-by: Fahad Alharbi <fahad@codepure.com>
Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
---
 net/unix/af_unix.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 6861370062df..2da1017f8873 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -2976,7 +2976,7 @@ static int unix_stream_read_generic(struct unix_stream_read_state *state,
 #if IS_ENABLED(CONFIG_AF_UNIX_OOB)
 		if (skb) {
 			skb = manage_oob(skb, &last, sk, flags, copied);
-			if (!skb && copied) {
+			if (!skb && (copied || !state->size)) {
 				unix_state_unlock(sk);
 				break;
 			}
-- 
2.55.0.970.g62bdec98f9-goog