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From:   Willem de Bruijn <willemdebruijn.kernel@gmail.com>
Date:   Fri, 4 Jan 2019 12:24:18 -0500
Message-ID: <CAF=yD-LdShBqHz1amBAAAA4w==0O+HfeWutfLi5K6LmWhK_x6Q@mail.gmail.com>
Subject: Re: kernel panic: stack is corrupted in udp4_lib_lookup2
To:     Stefano Brivio <sbrivio@redhat.com>
Cc:     Dmitry Vyukov <dvyukov@google.com>,
        Eric Dumazet <eric.dumazet@gmail.com>,
        syzbot <syzbot+4ad25edc7a33e4ab91e0@syzkaller.appspotmail.com>,
        David Miller <davem@davemloft.net>,
        Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Network Development <netdev@vger.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
        Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>
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On Fri, Jan 4, 2019 at 12:14 PM Stefano Brivio <sbrivio@redhat.com> wrote:
>
> On Fri, 4 Jan 2019 12:05:04 +0100
> Dmitry Vyukov <dvyukov@google.com> wrote:
>
> > On Fri, Jan 4, 2019 at 11:54 AM Stefano Brivio <sbrivio@redhat.com> wrote:
> > >
> > > On Fri, 4 Jan 2019 11:32:12 +0100
> > > Dmitry Vyukov <dvyukov@google.com> wrote:
> > >
> > > > On Thu, Jan 3, 2019 at 10:54 PM Stefano Brivio <sbrivio@redhat.com> wrote:
> > > > >
> > > > > On Thu, 3 Jan 2019 15:15:06 -0600
> > > > > Willem de Bruijn <willemdebruijn.kernel@gmail.com> wrote:
> > > > >
> > > > > > syzbot generated stack traces with
> > > > > >
> > > > > > [  183.517380]  udpv6_err+0x46/0x60
> > > > > > [  183.520739]  ? __udp6_lib_err+0x1890/0x1890
> > > > > > [  183.525054]  gue6_err_proto_handler+0x199/0x280
> > > > >
> > > > > Where? I can't find that in any logs linked from the dashboard at
> > > > > https://syzkaller.appspot.com/bug?extid=4ad25edc7a33e4ab91e0 :(
> > > >
> > > > Stefano, there are these 4 bugs reported that have similarly looking
> > > > reproducers involving udp sockets and that crash modes that looks like
> > > > stack corruption/overflow:
> > > >
> > > > https://syzkaller.appspot.com/bug?extid=14005fa30c9a07192934
> > > > https://syzkaller.appspot.com/bug?extid=d14090007dc9ba5fa9b7
> > > > https://syzkaller.appspot.com/bug?extid=137ed32ec9a6d5b0d5fe
> > > > https://syzkaller.appspot.com/bug?id=d5bc3e0c66d200d72216ab343a67c4327e4a3452
> > > >
> > > > Are these the same bug as this?
> > >
> > > Judging from the reproducers for the first three, they seem to be.
> >
> > OK, then I will mark them as dups of this one.
>
> syzbot just finished the tests I requested and couldn't reproduce the
> first three issues with the fix I posted (fou6: Prevent unbounded
> recursion in GUE error handler).

Thanks for preparing the fixes so quickly, Stefano.

I also noticed one trace that seemingly goes through an ip6erspan
tunnel as well as gue6.

[  760.618683]  ? __udp6_lib_err+0xcb/0x640
[  760.622716]  ? udplitev6_err+0x46/0x60
[  760.626573]  ? gue6_err+0x105/0x270
[  760.630170]  ? udp_lib_close+0x20/0x20
[  760.634027]  ? ip6erspan_tunnel_xmit+0xdc0/0xdc0

Without knowing the err_handler code too well: is it possible that
packets with an intermediate IPIP or other tunnel still bypass the
checks (which check for strictly UDP in GUE)?