netdev - Re: use-after-free in sctp_do

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Date:	Mon, 7 Dec 2015 16:52:18 -0200
From:	Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
To:	Dmitry Vyukov <dvyukov@...gle.com>
Cc:	Vlad Yasevich <vyasevich@...il.com>,
	netdev <netdev@...r.kernel.org>,
	Eric Dumazet <eric.dumazet@...il.com>,
	syzkaller <syzkaller@...glegroups.com>,
	linux-sctp@...r.kernel.org, Kostya Serebryany <kcc@...gle.com>,
	Alexander Potapenko <glider@...gle.com>,
	Sasha Levin <sasha.levin@...cle.com>
Subject: Re: use-after-free in sctp_do_sm

On Mon, Dec 07, 2015 at 02:20:47PM +0100, Dmitry Vyukov wrote:
> On Mon, Dec 7, 2015 at 2:15 PM, Marcelo Ricardo Leitner
> <marcelo.leitner@...il.com> wrote:
> > On Mon, Dec 07, 2015 at 12:26:09PM +0100, Dmitry Vyukov wrote:
> >> On Sat, Dec 5, 2015 at 5:39 PM, Vlad Yasevich <vyasevich@...il.com> wrote:
...
> >> > Hi Marcelo
> >> >
> >> > I think you also need to catch the SCTP_DISPOSITION_ABORT and update
> >> > the pointer.  There are some issues there though as some functions report
> >> > that code without actually destroying the association.  This happens when
> >> > the ABORT chunk may be dropped.
> >> >
> >> > I think this might be why we still see the issue.
> >>
> >>
> >> Marcelo,
> >>
> >> Is this info enough for you to cook another fix?
> >
> > Hi, I think so. I was really wondering how you could trigger that issue
> > without the timestamp fix and Vlad's comment does shed some light on it.
> >
> > I'll do more tests later today, but what did you have connecting to the
> > listening socket? Somehow you made that accept() call to return..
> 
> Local connect in another thread I guess.

Vlad, I reviewed the places on which it returns SCTP_DISPOSITION_ABORT,
and if I didn't miss something in there all of them either issue
SCTP_CMD_ASSOC_FAILED or SCTP_CMD_INIT_FAILED before returning it, thus
delaying DELETE_TCB and with that the asoc free. There is one place,
though, that may not do it that way, it's sctp_sf_abort_violation(), but
then that code only runs if asoc is already NULL by then.

Dmitry, still no luck here, cannot reproduce another hit.
I'm using sctp_test and a custom test of mine, both on localhost so I
would catch it in server or client side, nothing..

I need more info. Please enable the pr_debug() on debug_post_sfn() macro
and see which status is being reported when you trigger the issue.
And/or share a traffic capture so we can see what's going on with the
association.

  Marcelo
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