linux-kernel - Re: KASAN: slab-out-of-bounds Read in __nla_put

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Date:   Wed, 22 Jan 2020 12:27:11 -0800
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     syzbot <syzbot+5af9a90dad568aa9f611@...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>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>
Subject: Re: KASAN: slab-out-of-bounds Read in __nla_put_nohdr

On Tue, Jan 21, 2020 at 11:55 AM Eric Dumazet <eric.dumazet@...il.com> wrote:
> em_nbyte_change() sets
> em->datalen = sizeof(*nbyte) + nbyte->len;
>
> But later tcf_em_validate() overwrites em->datalen with the user provide value (em->datalen = data_len; )
> which can be bigger than the allocated (kmemdup) space in em_nbyte_change()
>
> Should net/sched/em_nbyte.c() provide a dump() handler to avoid this issue ?

I think for those who implement ->change() we should leave
->datalen untouched to respect their choices. I don't see why
we have to set it twice.

Thanks.