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

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Date:   Fri, 7 Sep 2018 03:48:54 +0900
From:   Taehee Yoo <ap420073@...il.com>
To:     Eric Dumazet <edumazet@...gle.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()

2018-09-07 3:23 GMT+09:00 Eric Dumazet <edumazet@...gle.com>:
> On Thu, Sep 6, 2018 at 11:06 AM Eric Dumazet <edumazet@...gle.com> wrote:
>>
>> 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.
>
> Something like that :
>
> diff --git a/net/ipv4/ip_fragment.c b/net/ipv4/ip_fragment.c
> index 88281fbce88ce8f1062b99594665766c2a5f5b74..e7227128df2c8fd54727c234f76043133809bd1e
> 100644
> --- a/net/ipv4/ip_fragment.c
> +++ b/net/ipv4/ip_fragment.c
> @@ -599,6 +599,7 @@ static int ip_frag_reasm(struct ipq *qp, struct
> sk_buff *skb,
>                         nextp = &fp->next;
>                         fp->prev = NULL;
>                         memset(&fp->rbnode, 0, sizeof(fp->rbnode));
> +                       fp->sk = NULL;
>                         head->data_len += fp->len;
>                         head->len += fp->len;
>                         if (head->ip_summed != fp->ip_summed)

Hi Eric!

Oh I'm sorry, I realized that ip_defrag_offset would be conflicting
with the rbnode just now
So, this patch should be dropped.
And I will make v2 patch regard you suggested!

Thank you for review and suggestion!