linux-kernel - Re: KASAN: use-after-free Read in br_mdb_ip

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Message-ID: <20190529152650.mjzyd6evzmonymj6@gondor.apana.org.au>
Date:   Wed, 29 May 2019 23:26:50 +0800
From:   Herbert Xu <herbert@...dor.apana.org.au>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     Nikolay Aleksandrov <nikolay@...ulusnetworks.com>,
        Thomas Graf <tgraf@...g.ch>,
        syzbot <syzbot+bc5ab0af2dbf3b0ae897@...kaller.appspotmail.com>,
        bridge@...ts.linux-foundation.org,
        David Miller <davem@...emloft.net>,
        LKML <linux-kernel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>,
        Roopa Prabhu <roopa@...ulusnetworks.com>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>
Subject: Re: KASAN: use-after-free Read in br_mdb_ip_get

On Wed, May 29, 2019 at 05:14:17PM +0200, Dmitry Vyukov wrote:
>
> > It looks like
> >
> > ommit 1515a63fc413f160d20574ab0894e7f1020c7be2
> > Author: Nikolay Aleksandrov <nikolay@...ulusnetworks.com>
> > Date:   Wed Apr 3 23:27:24 2019 +0300
> >
> >     net: bridge: always clear mcast matching struct on reports and leaves
> >
> > may have at least fixed the uninitialised value error.
> 
> 
> The most up-to-date info is always available here:
> 
> >> dashboard link: https://syzkaller.appspot.com/bug?extid=bc5ab0af2dbf3b0ae897
> 
> It says no new crashes happened besides the original one.
> 
> We now have the following choices:
> 
> 1. Invalidate with "#syz invalid"
> 2. Mark as tentatively fixed by that commit (could it fix it?) with
> "#syz fix: net: bridge: always clear mcast matching struct on reports
> and leaves"
> 3. Do nothing, then syzbot will auto-close it soon (bugs without
> reproducers that did not happen in the past 180 days)

I'm still not quite sure how this could cause the use-after-free,
but it certainly seems to be the cause for the second issue of
uninit-value:

https://syzkaller.appspot.com/bug?extid=8dfe5ee27aa6d2e396c2

And this one does seem to have occured again recently (two months
ago).

Thanks,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt