linux-kernel - Re: [syzbot] UBSAN: shift-out-of-bounds in tcf_pedit

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Message-ID: <20220512155136.70554388@kernel.org>
Date:   Thu, 12 May 2022 15:51:36 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     syzbot <syzbot+8ed8fc4c57e9dcf23ca6@...kaller.appspotmail.com>,
        David Miller <davem@...emloft.net>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Jiri Pirko <jiri@...nulli.us>,
        LKML <linux-kernel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>, Paolo Abeni <pabeni@...hat.com>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Cong Wang <xiyou.wangcong@...il.com>
Subject: Re: [syzbot] UBSAN: shift-out-of-bounds in tcf_pedit_init

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@...glegroups.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@...hat.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.