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

From: Rainer Weikusat
Date: Mon Feb 08 2016 - 13:47:45 EST


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.

Fixes: 3822b5c2fc62 ("af_unix: Revert 'lock_interruptible' in stream receive code")
Reported-by: Joseph Salisbury <joseph.salisbury@xxxxxxxxxxxxx>
Signed-off-by: Rainer Weikusat <rweikusat@xxxxxxxxxxxxxxxxxxxxxxx>
---

And the subject again fixed and, since another correction was necessary,
anyway, a Reported-by added.

diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 49d5093..c1e4dd7 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -2277,13 +2277,15 @@ static int unix_stream_read_generic(struct unix_stream_read_state *state)
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);
@@ -2329,9 +2331,11 @@ 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,