Messages in this thread | | | Date | Wed, 6 Jan 2016 23:11:41 +0300 | Subject | Re: [BUG] skb corruption and kernel panic at forwarding with fragmentation | From | Konstantin Khlebnikov <> |
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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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