Am Freitag, 1. November 2013, 09:25:37 schrieb Patrick McHardy:
> On Fri, Nov 01, 2013 at 09:45:29AM +0100, Steffen Klassert wrote:
> > On Wed, Oct 30, 2013 at 12:07:11AM +0000, Patrick McHardy wrote:
> > > The problem is that the reassembled packet is referenced by the
> > > individual
> > > fragments, so we trigger the BUG_ON in pskb_expand_head(). In this
> > > particular case the case we BUG() on is actually OK, but I'm looking at
> > > a way we can fix this without special casing. Hope to have a patch for
> > > testing in the next hours.
> >
> > Just for the record. I'm observing similar, quite reproducable crashes
> > when
> > receiving fragmented icmp echo request packets on an IPsec gateway with
> > nf_conntrack_ipv6.
> >
> > Since git commit 58a317f10 ("netfilter: ipv6: add IPv6 NAT support")
> > netfilter might insert a reassembled ipv6 packet with a shared skb and
> > local_df = 1 to the ok function. In case of xfrm, __xfrm6_output()
> > fragments the packet again and when adjusting the headroom later, we
> > crash because of a shared skb.
> >
> > I can fix it by checking for a shared skb in ip6_fragment() and do
> > slow path fragmentation then. But we never needed such a check in
> > ip6_fragment(), so it's maybe better to fix it in netfilter.
>
> So what seems to be happening is that this case in __ipv6_conntrack_in()
> triggers:
>
> /* Conntrack helpers need the entire reassembled packet in the
> * POST_ROUTING hook. In case of unconfirmed connections NAT
> * might reassign a helper, so the entire packet is also
> * required.
> */
> ct = nf_ct_get(reasm, &ctinfo);
> if (ct != NULL && !nf_ct_is_untracked(ct)) {
> help = nfct_help(ct);
> if ((help && help->helper) || !nf_ct_is_confirmed(ct)) {
> nf_conntrack_get_reasm(reasm);
> NF_HOOK_THRESH(NFPROTO_IPV6, hooknum, reasm,
> (struct net_device *)in,
> (struct net_device *)out,
> okfn, NF_IP6_PRI_CONNTRACK + 1);
>
> Since this code is called while walking through the fragment chain, we have
> extra references to the reassembled skb. So I think what we need to do is
> to release the fragment chain before calling NF_HOOK_THRESH() and indicate
> this to nf_ct_frag6_output() so it will stop processing the chain
> immediately.
>
> I'll give it a try, will let you know when I have a patch for testing.
> --
> To unsubscribe from this list: send the line "unsubscribe netdev" in
> the body of a message to majordomo@xxxxxxxxxxxxxxx
> More majordomo info at http://vger.kernel.org/majordomo-info.html
Are there patches available? I can crash my 3.12 kernel easily doing
fping -p 20 -l -b 4000 bla
3.11.x does not expose this problem.
Regards,
--
Wolfgang Walter
Studentenwerk München
Anstalt des öffentlichen Rechts
--
To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
