On Wed, Mar 23, 2011 at 6:49 PM, Feng Gao <kernel.goter@xxxxxxxxx> wrote:
> 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.
>
>
Have you ever tested that? I am afraid no panic will happen.
nf_ct_kill_acct() just drops the reference owned by the corresponding
timeout timer to the ct if the timer is installed, so the skb still
has the reference to the ct after nf_ct_kill_acct() returns. Thanks.
BTW: all the patches related to netfilter should be sent to the
netfilter developer mailing list.
--
Regards,
Changli Gao(xiaosuo@xxxxxxxxx)
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