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From:   Eric Dumazet <edumazet@google.com>
Date:   Thu, 12 May 2022 16:53:19 -0700
Message-ID: <CANn89i+xqQafpRrF7=G0FqJNZkQUBCt_sKsSbhG64bq0iCnztQ@mail.gmail.com>
Subject: Re: [syzbot] UBSAN: shift-out-of-bounds in tcf_pedit_init
To:     Jakub Kicinski <kuba@kernel.org>
Cc:     syzbot <syzbot+8ed8fc4c57e9dcf23ca6@syzkaller.appspotmail.com>,
        David Miller <davem@davemloft.net>,
        Jamal Hadi Salim <jhs@mojatatu.com>,
        Jiri Pirko <jiri@resnulli.us>,
        LKML <linux-kernel@vger.kernel.org>,
        netdev <netdev@vger.kernel.org>, Paolo Abeni <pabeni@redhat.com>,
        syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
        Cong Wang <xiyou.wangcong@gmail.com>
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On Thu, May 12, 2022 at 3:51 PM Jakub Kicinski <kuba@kernel.org> wrote:
>
> On Thu, 12 May 2022 14:19:51 -0700 Eric Dumazet wrote:
> > On Thu, May 12, 2022 at 2:18 PM syzbot
> > > This report is generated by a bot. It may contain errors.
> > > See https://goo.gl/tpsmEJ for more information about syzbot.
> > > syzbot engineers can be reached at syzkaller@googlegroups.com.
> > >
> > > syzbot will keep track of this issue. See:
> > > https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> > > syzbot can test patches for this issue, for details see:
> > > https://goo.gl/tpsmEJ#testing-patches
> >
> > As mentioned earlier, this came with
> >
> > commit 8b796475fd7882663a870456466a4fb315cc1bd6
> > Author: Paolo Abeni <pabeni@redhat.com>
> > Date:   Tue May 10 16:57:34 2022 +0200
> >
> >     net/sched: act_pedit: really ensure the skb is writable
>
> Came in as in new stack trace for an old/existing bug, right?
> Nothing checks the shift so it'd have already tripped UBSAN
> later on in tcf_pedit_act(), anyway.

Maybe a prior syzbot was reported, and nobody cared.

Or maybe syzbot got its way into this path only recently.