af_unix: Don't set err in unix_stream_read_generic unless there was an error
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@canonical.com>
Signed-off-by: Rainer Weikusat <rweikusat@mobileactivedefense.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>