Re: [PATCH net] openvswitch: Fix skb leak in IPv6 reassembly.

[Joe Stringer <joe@ovn.org>]

On 28 November 2016 at 16:45, Florian Westphal <fw@strlen.de> wrote:
> Eric Dumazet <eric.dumazet@gmail.com> wrote:
>> On Mon, 2016-11-28 at 15:43 -0800, Daniele Di Proietto wrote:
>> > If nf_ct_frag6_gather() returns an error other than -EINPROGRESS, it
>> > means that we still have a reference to the skb.  We should free it
>> > before returning from handle_fragments, as stated in the comment above.
>> >
>> > Fixes: daaa7d647f81 ("netfilter: ipv6: avoid nf_iterate recursion")
>> > CC: Florian Westphal <fw@strlen.de>
>> > CC: Pravin B Shelar <pshelar@ovn.org>
>> > CC: Joe Stringer <joe@ovn.org>
>> > Signed-off-by: Daniele Di Proietto <diproiettod@ovn.org>
>> > ---
>> >  net/openvswitch/conntrack.c | 5 ++++-
>> >  1 file changed, 4 insertions(+), 1 deletion(-)
>> >
>> > diff --git a/net/openvswitch/conntrack.c b/net/openvswitch/conntrack.c
>> > index 31045ef..fecefa2 100644
>> > --- a/net/openvswitch/conntrack.c
>> > +++ b/net/openvswitch/conntrack.c
>> > @@ -370,8 +370,11 @@ static int handle_fragments(struct net *net, struct sw_flow_key *key,
>> >             skb_orphan(skb);
>> >             memset(IP6CB(skb), 0, sizeof(struct inet6_skb_parm));
>> >             err = nf_ct_frag6_gather(net, skb, user);
>> > -           if (err)
>> > +           if (err) {
>> > +                   if (err != -EINPROGRESS)
>> > +                           kfree_skb(skb);
>> >                     return err;
>> > +           }
>> >
>> >             key->ip.proto = ipv6_hdr(skb)->nexthdr;
>> >             ovs_cb.mru = IP6CB(skb)->frag_max_size;
>>
>> Interesting, have you followed the "GPF in eth_header" thread today ?
>>
>> In a nutshell, we want a complete patch, not something that would solve
>> part of the problem.
>
> I think this patch is fine, intent seems to be to only take fully reassembled
> skb, rather than a stray fragment (ovs does NOT seem to call handle_fragments
> in case skb is already known to not contain a fragment header, afaics).

Correct, this is used in OVS only for fragmented packets and this
function either morphs the skb into the full skb fragment chain, or
steals/frees the skb.

> I'll send a patch for the GPF in eth_header thing soon.