Subject: Re: Reported regression against commit a05d2ad

From: [email-masked] (Eric W. Biederman)
Date: Tue, 21 Jun 2011 13:49:45 -0700

Herton Ronaldo Krzesinski <[email-masked]> writes:

> Hi,
>
> after update to one of the latest 2.6.32.x stable kernels for Ubuntu, we
> got a regression report about timeout in tcp connections
> (https://launchpad.net/bugs/791512).
>
> We tried help reporter with a bisect process, but it was taking some
> time, so we reverted some suspect commits, until we isolated it to
> commit "af_unix: Only allow recv on connected seqpacket sockets."
>
> With only commit a05d2ad reverted, testing results so far indicate the
> issue doesn't happen.
>
> I'm unfamiliar with unix sockets code, so can't see at first why this
> commit in particular is causing problems, for now I can only say may be
> something at application level using unix sockets regressed with it (?).
> I'm just reporting it right now, and we plan to revert it for that kernel
> until more info is found about it.

The only thing commit a05d2ad will prevent is a non-sense use of a
af_unix socket, and on recent enough kernels a NULL pointer deference.

I respectfully suggest that the bug is elsewhere perhaps a broken user
space application out there that needs to be fixed, or you have a kernel
memory stomp that removing patch a05d2ad happens to shift the memory
layout to be harmful in a different way.

af_unix sockets have nothing to do with tcp and only happen to use
the TCP_ESTABLISHED flag to indicated connected or non-connected
sockets.

Eric

> I'm adding reporter to CC (Lamont), in case more details are necessary
> etc.