linux-kernel - Re: bpf-next boot error: KASAN: use-after-free Write in call_usermodehelper_exec

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Date:   Thu, 7 Jun 2018 20:12:22 +0200
From:   "Luis R. Rodriguez" <mcgrof@...nel.org>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Dmitry Vyukov <dvyukov@...gle.com>,
        syzbot <syzbot+2c73319c406f1987d156@...kaller.appspotmail.com>,
        Alexei Starovoitov <ast@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>, mcgrof@...nel.org,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Daniel Borkmann <daniel@...earbox.net>
Subject: Re: bpf-next boot error: KASAN: use-after-free Write in
 call_usermodehelper_exec_work

On Thu, Jun 07, 2018 at 09:07:01AM -0700, Alexei Starovoitov wrote:
> On Thu, Jun 07, 2018 at 02:19:16PM +0200, Dmitry Vyukov wrote:
> > On Mon, Jun 4, 2018 at 10:21 PM, syzbot
> > <syzbot+2c73319c406f1987d156@...kaller.appspotmail.com> wrote:
> > > Hello,
> > >
> > > syzbot found the following crash on:
> > >
> > > HEAD commit:    69b450789136 Merge branch 'misc-BPF-improvements'
> > > git tree:       bpf-next
> > > console output: https://syzkaller.appspot.com/x/log.txt?x=1080d1d7800000
> > > kernel config:  https://syzkaller.appspot.com/x/.config?x=e4078980b886800c
> > > dashboard link: https://syzkaller.appspot.com/bug?extid=2c73319c406f1987d156
> > > compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
> > >
> > > Unfortunately, I don't have any reproducer for this crash yet.
> > >
> > > IMPORTANT: if you fix the bug, please add the following tag to the commit:
> > > Reported-by: syzbot+2c73319c406f1987d156@...kaller.appspotmail.com
> > 
> > 
> > This crash now happens on every other boot of mainline tree. This
> > prevents syzbot testing of new code, and just boots machine with
> > corrupted memory. Were there any recent changes in umh? +Alexei, you
> > seem to touch it last. Could your change cause this?
> 
> looking into it. I think I see the issue. Trying to reproduce.

And this is why a test driver would be useful ;)

  Luis