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Re: [BUG] skb corruption and kernel panic at forwarding with fragmentation

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On Wed, Jan 6, 2016 at 10:59 PM, Cong Wang <xiyou.wangcong@gmail.com> wrote:
> On Wed, Jan 6, 2016 at 11:15 AM, Konstantin Khlebnikov <koct9i@gmail.com> wrote:
>> Looks like this happens because ip_options_fragment() relies on
>> correct ip options length in ip control block in skb. But in
>> ip_finish_output_gso() control block in segments is reused by
>> skb_gso_segment(). following ip_fragment() sees some garbage.
>>
>> In my case there was no ip options but length becomes non-zero and
>> ip_options_fragment() picked some bytes from payload and decides to
>> fill huge range with IPOPT_NOOP (1). One of that ones flipped nr_frags
>> in skb_shared_info at the end of data =)
>>
>
> Hmm, it looks like SKB_GSO_CB should be cleared after skb_gso_segment()
> since all the gso information should be saved in shared_info after it finishes.
>
> Does a memset(0) on SKB_GSO_CB after skb_gso_segment() work as well?

This will break present logic around ip_options_fragment() - it clears
options from
second and following fragments. With zeroed cb it will do nothing.

ip_options_fragment() can get required information directly from ip header but
it also resets fields in IPCB -- probably it should stay valid here
and somebody else will use it later.
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Thread

[BUG] skb corruption and kernel panic at forwarding with fragmentation Konstantin Khlebnikov <koct9i@gmail.com> - 2016-01-06 20:20 +0100
  Re: [BUG] skb corruption and kernel panic at forwarding with fragmentation Cong Wang <xiyou.wangcong@gmail.com> - 2016-01-06 21:00 +0100
    Re: [BUG] skb corruption and kernel panic at forwarding with fragmentation Konstantin Khlebnikov <koct9i@gmail.com> - 2016-01-06 21:20 +0100
      Re: [BUG] skb corruption and kernel panic at forwarding with  fragmentation Thadeu Lima de Souza Cascardo <cascardo@redhat.com> - 2016-01-06 22:10 +0100
        Re: [BUG] skb corruption and kernel panic at forwarding with  fragmentation Florian Westphal <fw@strlen.de> - 2016-01-06 23:10 +0100
          Re: [BUG] skb corruption and kernel panic at forwarding with  fragmentation Florian Westphal <fw@strlen.de> - 2016-01-07 01:00 +0100
            Re: [BUG] skb corruption and kernel panic at forwarding with fragmentation Konstantin Khlebnikov <koct9i@gmail.com> - 2016-01-07 12:10 +0100
              Re: [BUG] skb corruption and kernel panic at forwarding with fragmentation Konstantin Khlebnikov <koct9i@gmail.com> - 2016-01-07 12:40 +0100
                Re: [BUG] skb corruption and kernel panic at forwarding with fragmentation Eric Dumazet <edumazet@google.com> - 2016-01-07 13:00 +0100
                Re: [BUG] skb corruption and kernel panic at forwarding with fragmentation Konstantin Khlebnikov <koct9i@gmail.com> - 2016-01-07 13:10 +0100
                Re: [BUG] skb corruption and kernel panic at forwarding with fragmentation Eric Dumazet <edumazet@google.com> - 2016-01-07 14:00 +0100
                Re: [BUG] skb corruption and kernel panic at forwarding with fragmentation Konstantin Khlebnikov <koct9i@gmail.com> - 2016-01-07 20:40 +0100
                Re: [BUG] skb corruption and kernel panic at forwarding with fragmentation Eric Dumazet <edumazet@google.com> - 2016-01-07 20:50 +0100
              Re: [BUG] skb corruption and kernel panic at forwarding with  fragmentation Florian Westphal <fw@strlen.de> - 2016-01-07 13:10 +0100
            [PATCH] net: prevent corruption of skb when using skb_gso_segment Thadeu Lima de Souza Cascardo <cascardo@redhat.com> - 2016-01-07 19:50 +0100
              Re: [PATCH] net: prevent corruption of skb when using skb_gso_segment Florian Westphal <fw@strlen.de> - 2016-01-07 20:40 +0100
                [PATCH v2] net: prevent corruption of skb when using skb_gso_segment Thadeu Lima de Souza Cascardo <cascardo@redhat.com> - 2016-01-07 22:20 +0100

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