linux-kernel - Re: net/sctp: list double add warning in sctp_endpoint_add

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Date:   Wed, 5 Apr 2017 11:22:05 -0300
From:   Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
To:     Andrey Konovalov <andreyknvl@...gle.com>
Cc:     Xin Long <lucien.xin@...il.com>,
        Vlad Yasevich <vyasevich@...il.com>,
        Neil Horman <nhorman@...driver.com>,
        "David S. Miller" <davem@...emloft.net>,
        linux-sctp@...r.kernel.org, netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Kostya Serebryany <kcc@...gle.com>,
        syzkaller <syzkaller@...glegroups.com>
Subject: Re: net/sctp: list double add warning in sctp_endpoint_add_asoc

On Wed, Apr 05, 2017 at 04:02:44PM +0200, Andrey Konovalov wrote:
> On Tue, Apr 4, 2017 at 11:14 PM, Marcelo Ricardo Leitner
> <marcelo.leitner@...il.com> wrote:
> > On Wed, Apr 05, 2017 at 01:29:19AM +0800, Xin Long wrote:
> >> On Tue, Apr 4, 2017 at 9:28 PM, Andrey Konovalov <andreyknvl@...gle.com> wrote:
> >> > Hi,
> >> >
> >> > I've got the following error report while fuzzing the kernel with syzkaller.
> >> >
> >> > On commit a71c9a1c779f2499fb2afc0553e543f18aff6edf (4.11-rc5).
> >> >
> >> > A reproducer and .config are attached.
> >> The script is pretty hard to reproduce the issue in my env.
> >
> > I didn't try running it but I also found the reproducer very complicated
> > to follow. Do you have any plans on having some PoC optimizer, so we can
> > have a more readable code?
> > strace is handy for filtering the noise, yes, but sometimes it doesn't
> > cut it.
> 
> We do have some plans (like to remote all those unnecessary helper
> functions), but it's probably not going to become much better.
> 
> You mostly only need to look at the thr() function to understand
> what's going on.

Okay.

> 
> What I sometimes do is run each of the switch cases under strace
> separately to understand what each of them do.
> 
> I've also attached a program in syzkaller format.
> You can take a look at it, if you find it useful, I can start
> attaching them for subsequent reports.

Comparing it to thr() they look very close, at least for this one.
But when you cannot extract a reproducer, it will certainly help.

Thanks,
Marcelo