netdev - Re: [PATCH net] ip: frags: fix crash in ip_do

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Message-ID: <CANn89iJENha1FiqA_pNpaXu-+vryHjw+6a-fR4Qc3-WmQsrXdQ@mail.gmail.com>
Date:   Thu, 6 Sep 2018 11:06:39 -0700
From:   Eric Dumazet <edumazet@...gle.com>
To:     ap420073@...il.com
Cc:     David Miller <davem@...emloft.net>,
        Peter Oskolkov <posk@...gle.com>,
        netdev <netdev@...r.kernel.org>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Florian Westphal <fw@...len.de>
Subject: Re: [PATCH net] ip: frags: fix crash in ip_do_fragment()

On Thu, Sep 6, 2018 at 10:51 AM Taehee Yoo <ap420073@...il.com> wrote:
>
> A kernel crash occurrs when defragmented packet is fragmented
> in ip_do_fragment().
> In defragment routine, skb_orphan() is called and
> skb->ip_defrag_offset is set. but skb->sk and
> skb->ip_defrag_offset are same union member. so that
> frag->sk is not NULL.
> Hence crash occurrs in skb->sk check routine in ip_do_fragment() when
> defragmented packet is fragmented.

Have you tested this patch ?

Moving back ip_defrag_offset is conflicting with the rbnode !

A more correct fix would be to properly clear skb->sk at reassembly.