[PATCH 3.13.y-ckt 137/138] af_unix: Don't set err in unix_stream_read_generic unless there was an error

From: Kamal Mostafa
Date: Wed Mar 09 2016 - 18:22:12 EST


3.13.11-ckt36 -stable review patch. If anyone has any objections, please let me know.

---8<------------------------------------------------------------

From: Rainer Weikusat <rweikusat@xxxxxxxxxxxxxxxxxxxxxxx>

commit 1b92ee3d03af6643df395300ba7748f19ecdb0c5 upstream.

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>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
[ luis: backported to 3.16:
- modify unix_stream_recvmsg() instead of unix_stream_read_generic()
- adjusted context ]
Signed-off-by: Luis Henriques <luis.henriques@xxxxxxxxxxxxx>

Signed-off-by: Kamal Mostafa <kamal@xxxxxxxxxxxxx>
---
net/unix/af_unix.c | 16 ++++++++++------
1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 3974413..17a824b 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -2089,13 +2089,15 @@ static int unix_stream_recvmsg(struct kiocb *iocb, struct socket *sock,
long timeo;
int skip;

- 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);
@@ -2143,9 +2145,11 @@ 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);
--
2.7.0