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Date:   Tue, 23 Apr 2019 15:06:45 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Tycho Andersen <tycho@...ho.ws>
Cc:     Alexei Starovoitov <ast@...nel.org>, bpf@...r.kernel.org,
        coreteam@...filter.org, Daniel Borkmann <daniel@...earbox.net>,
        "David S. Miller" <davem@...emloft.net>,
        Florian Westphal <fw@...len.de>,
        Jozsef Kadlecsik <kadlec@...ckhole.kfki.hu>,
        Martin KaFai Lau <kafai@...com>,
        LKML <linux-kernel@...r.kernel.org>,
        Andy Lutomirski <luto@...capital.net>,
        Network Development <netdev@...r.kernel.org>,
        netfilter-devel@...r.kernel.org,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Song Liu <songliubraving@...com>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Will Drewry <wad@...omium.org>, wenxu@...oud.cn,
        Yonghong Song <yhs@...com>,
        syzbot <syzbot+b562969adb2e04af3442@...kaller.appspotmail.com>
Subject: Re: KASAN: use-after-free Read in seccomp_notify_release (2)

On Tue, Apr 23, 2019 at 2:51 PM Tycho Andersen <tycho@...ho.ws> wrote:
>
> On Tue, Apr 23, 2019 at 02:39:52PM -0700, Kees Cook wrote:
> > On Mon, Mar 25, 2019 at 1:02 AM syzbot
> > <syzbot+b562969adb2e04af3442@...kaller.appspotmail.com> wrote:
> > >
> > > Hello,
> > >
> > > syzbot found the following crash on:
> > >
> > > HEAD commit:    1bdd3dbf Merge tag 'io_uring-20190323' of git://git.kernel..
> > > git tree:       upstream
> > > console output: https://syzkaller.appspot.com/x/log.txt?x=12ae5b93200000
> > > kernel config:  https://syzkaller.appspot.com/x/.config?x=9a31fb246de2a622
> > > dashboard link: https://syzkaller.appspot.com/bug?extid=b562969adb2e04af3442
> > > compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
> > > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=162ca25d200000
> > > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1733b53b200000
> > >
> > > The bug was bisected to:
> > >
> > > commit a799aea0988ea0d1b1f263e996fdad2f6133c680
> > > Author: wenxu <wenxu@...oud.cn>
> > > Date:   Wed Jan 9 02:40:11 2019 +0000
> > >
> > >      netfilter: nft_flow_offload: Fix reverse route lookup
> >
> > This bisection looks bogus?
> >
> > However, I _can_ trigger the problem on this kernel version with this
> > config. (And not with Linus's latest tree.)
> >
> > The PoC is identical to the prior report[1] that we thought was fixed.
> > Perhaps the fix didn't actually fix it? (I mean
> > a811dc61559e0c8003f1086c2a4dc8e4d5ae4cb8) But it's been silent for 29
> > days now, so I'm not sure what's going on.
> >
> > Tycho are you able to reproduce this on the older tree?
>
> It looks like this case is using TSYNC and NEW_LISTENER together:
>
> syscall(__NR_seccomp, 1, 0xb, 0x20000140);

Ah, thanks. My eye-diff didn't work. :)

> and I did fix a uaf with TSYNC and NEW_LISTENER in this series:
>
> https://lore.kernel.org/lkml/20190306201413.14153-2-tycho@tycho.ws/T/#u
>
> which seems like it's probably related. I don't think the above ever
> got applied though?

Whoops, I lost this. Let me go dig that up. Thanks!

-- 
Kees Cook

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