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

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@canonical.com>
Signed-off-by: Rainer Weikusat <rweikusat@mobileactivedefense.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 10 insertions, 6 deletions

diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 29be035f9c65..df923caa8389 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,