netdev - Re: [PATCH] ip_fragment:kernel may panic when replay big packet with RST flag

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Date:	Wed, 23 Mar 2011 19:37:06 +0800
From:	Feng Gao <kernel.goter@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH] ip_fragment:kernel may panic when replay big packet with
 RST flag

This patch is for 2.6.25.16.

2011/3/23 Feng Gao <kernel.goter@...il.com>:
> Sorry, I will google it.
> I find this problem in 2.4.35. and then I read the Latest code,maybe
> it has the same problem too.
>
> diff -Nur skbuff.h skbuff.h.frag
> --- skbuff.h    2008-08-21 02:16:14.000000000 +0800
> +++ skbuff.h.frag       2011-03-23 19:30:20.000000000 +0800
> @@ -1754,6 +1754,20 @@
>        __nf_copy(dst, src);
>  }
>
> +/* This func for ip_fragment deal with RST packet */
> +static inline void nf_copy_rst(struct sk_buff *dst, const struct sk_buff *src)
> +{
> +#if defined(CONFIG_NF_CONNTRACK) || defined(CONFIG_NF_CONNTRACK_MODULE)
> +       nf_conntrack_put(dst->nfct);
> +       nf_conntrack_put_reasm(dst->nfct_reasm);
> +#endif
> +#ifdef CONFIG_BRIDGE_NETFILTER
> +       nf_bridge_put(dst->nf_bridge);
> +       dst->nf_bridge  = src->nf_bridge;
> +       nf_bridge_get(src->nf_bridge);
> +#endif
> +}
> +
>  #ifdef CONFIG_NETWORK_SECMARK
>  static inline void skb_copy_secmark(struct sk_buff *to, const struct
> sk_buff *from)
>  {
>
> diff -Nur ip_output.c ip_output.c.frag
> --- ip_output.c 2008-08-21 02:16:14.000000000 +0800
> +++ ip_output.c.frag    2011-03-23 19:27:57.000000000 +0800
> @@ -413,7 +413,14 @@
>  #ifdef CONFIG_NET_SCHED
>        to->tc_index = from->tc_index;
>  #endif
> -       nf_copy(to, from);
> +       struct tcphdr *th = (struct tcphdr *)((char *)iph + (iph->ihl << 2));
> +       if(iph->protocol == IPPROTO_TCP && th->rst){
> +               /*RST packet*/
> +               nf_copy_rst(to, from);
> +       }else{
> +                /*Other packet*/
> +               nf_copy(to, from);
> +       }
>  #if defined(CONFIG_NETFILTER_XT_TARGET_TRACE) || \
>     defined(CONFIG_NETFILTER_XT_TARGET_TRACE_MODULE)
>        to->nf_trace = from->nf_trace;
>
> 2011/3/23 Eric Dumazet <eric.dumazet@...il.com>:
>> Le mercredi 23 mars 2011 à 18:49 +0800, Feng Gao a écrit :
>>> Hello everyone:
>>>
>>> PC(A)-linux(B)-PC(C)
>>> computer(linux B) with two net interface,eth0 and eth1.
>>> PC(A) send syn to PC(C)  though linux B.
>>> then PC(C) replay a big packet  with RST flag(use tcpsic or other tools).
>>>
>>> This RST packet(1480) come in from eth0(mtu 1500) and go out from
>>> eth1(mtu 700), so this RST packet should fragment.
>>>
>>> BUT in tcp_packet func: if the connection has no reply packet,and
>>> receive the RST packet.ip_conntrack should  destroy.
>>>   if (!test_bit(IPS_SEEN_REPLY_BIT, &ct->status)) {
>>>                 /* If only reply is a RST, we can consider ourselves not to
>>>                    have an established connection: this is a fairly common
>>>                    problem case, so we can delete the conntrack
>>>                    immediately.  --RR */
>>>                 if (th->rst) {
>>>                         nf_ct_kill_acct(ct, ctinfo, skb);
>>>                         return NF_ACCEPT;
>>>                 }
>>>         }
>>>
>>> BUT the skb->nfct is not set NULL in func nf_ct_kill_acct.
>>> so when this RST packet goto ip_fragment,ip_fragment call nf_copy, in
>>> __nf_copy func
>>> the fragment skb->nfct point to the destory mem.
>>> dst->nfct = src->nfct;
>>> nf_conntrack_get(src->nfct);
>>>
>>> SO finally.kfree_skb call destroy_conntrack again. this may result in
>>> LINUX B kernel panic.
>>>
>>>
>>> here is the patch,sorry ,i dont know how to use diff to generate patch.
>>> :-D
>>>
>>
>> Hi Feng
>>
>> Oh well, please learn how to do this. If you are able to make such
>> analysis, you sure can learn how to use diff !!!
>>
>> What is the version of linux you use ?
>>
>>
>>
>>
>
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