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

From: Rainer Weikusat
Date: Fri Feb 05 2016 - 17:30:24 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.

Signed-off-by: Rainer Weikusat <rweikusat@xxxxxxxxxxxxxxxxxxxxxxx>
---

With proper subject this time (at least I hope so).

diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 49d5093..138787d 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 (sk->sk_state != TCP_ESTABLISHED) {
+ err = -EINVAL;
goto out;
+ }

- err = -EOPNOTSUPP;
- if (flags & MSG_OOB)
+ if (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,