Patch "af_unix: Don't set err in unix_stream_read_generic unless there was an error" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

af_unix: Don't set err in unix_stream_read_generic unless there was an error

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
af_unix-don-t-set-err-in-unix_stream_read_generic-unless-there-was-an-error.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Rainer Weikusat <[email protected]>
Date: Mon, 8 Feb 2016 18:47:19 +0000
Subject: af_unix: Don't set err in unix_stream_read_generic unless there was an error

From: Rainer Weikusat <[email protected]>

[ Upstream commit 1b92ee3d03af6643df395300ba7748f19ecdb0c5 ]

The present unix_stream_read_generic contains various code sequences of the form

err = -EDISASTER;
if (<test>)

	goto out;

This has the unfortunate side effect of possibly causing the error code to bleed through to the final

out:

	return copied ? : err;

and then to be wrongly returned if no data was copied because the caller didn't supply a data buffer, as demonstrated by the program available at

http://pad.lv/1540731

Change it such that err is only set if an error condition was detected.

---
 net/unix/af_unix.c |   16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

@@ -2270,13 +2270,15 @@ static int unix_stream_read_generic(stru
 	size_t size = state->size;
 	unsigned int last_len;
 
-	err = -EINVAL;
-	if (sk->sk_state != TCP_ESTABLISHED)
+	if (unlikely(sk->sk_state != TCP_ESTABLISHED)) {
+		err = -EINVAL;
 		goto out;
+	}
 
-	err = -EOPNOTSUPP;
-	if (flags & MSG_OOB)
+	if (unlikely(flags & MSG_OOB)) {
+		err = -EOPNOTSUPP;
 		goto out;
+	}
 
 	target = sock_rcvlowat(sk, flags & MSG_WAITALL, size);
 	timeo = sock_rcvtimeo(sk, noblock);

@@ -2322,9 +2324,11 @@ again:
 				goto unlock;
 
 			unix_state_unlock(sk);
-			err = -EAGAIN;
-			if (!timeo)
+			if (!timeo) {
+				err = -EAGAIN;
 				break;
+			}
+
 			mutex_unlock(&u->readlock);
 
 			timeo = unix_stream_data_wait(sk, timeo, last,

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/af_unix-don-t-set-err-in-unix_stream_read_generic-unless-there-was-an-error.patch queue-4.4/af_unix-fix-struct-pid-memory-leak.patch queue-4.4/af_unix-guard-against-other-sk-in-unix_dgram_sendmsg.patch