Re: [syzbot] UBSAN: shift-out-of-bounds in tcf_pedit_init

[Eric Dumazet]

On Thu, May 12, 2022 at 3:51 PM Jakub Kicinski <kuba@xxxxxxxxxx> 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.
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> > > syzbot engineers can be reached at syzkaller@xxxxxxxxxxxxxxxx.
> > >
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> >
> > As mentioned earlier, this came with
> >
> > commit 8b796475fd7882663a870456466a4fb315cc1bd6
> > Author: Paolo Abeni <pabeni@xxxxxxxxxx>
> > 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.