> On Apr 19, 2017, at 3:30 AM, Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx> wrote:
>
> On Tue, Apr 18, 2017 at 12:24:28PM -0700, Joe Stringer wrote:
>> On 18 April 2017 at 11:33, Jarno Rajahalme <jarno@xxxxxxx> wrote:
>>>
>>>> On Apr 18, 2017, at 11:27 AM, Joe Stringer <joe@xxxxxxx> wrote:
>>>>
>>>> On 14 April 2017 at 14:26, Jarno Rajahalme <jarno@xxxxxxx> wrote:
>>>>> Conntrack helpers do not check for a potentially clashing conntrack
>>>>> entry when creating a new expectation. Also, nf_conntrack_in() will
>>>>> check expectations (via init_conntrack()) only if a conntrack entry
>>>>> can not be found. The expectation for a packet which also matches an
>>>>> existing conntrack entry will not be removed by conntrack, and is
>>>>> currently handled inconsistently by OVS, as OVS expects the
>>>>> expectation to be removed when the connection tracking entry matching
>>>>> that expectation is confirmed.
>>>>>
>>>>> It should be noted that normally an IP stack would not allow reuse of
>>>>> a 5-tuple of an old (possibly lingering) connection for a new data
>>>>> connection, so this is somewhat unlikely corner case. However, it is
>>>>> possible that a misbehaving source could cause conntrack entries be
>>>>> created that could then interfere with new related connections.
>>>>>
>>>>> Fix this in the OVS module by deleting the clashing conntrack entry
>>>>> after an expectation has been matched. This causes the following
>>>>> nf_conntrack_in() call also find the expectation and remove it when
>>>>> creating the new conntrack entry, as well as the forthcoming reply
>>>>> direction packets to match the new related connection instead of the
>>>>> old clashing conntrack entry.
>>>>>
>>>>> Fixes: 7f8a436eaa2c ("openvswitch: Add conntrack action")
>>>>> Reported-by: Yang Song <yangsong@xxxxxxxxxx>
>>>>> Signed-off-by: Jarno Rajahalme <jarno@xxxxxxx>
>>>>> ---
>>>>
>>>> Hi Jarno,
>>>>
>>>>> v3: Removed unnecessary if statement.
>>>>> v2: Fixed commit title.
>>>>>
>>>>> net/openvswitch/conntrack.c | 31 ++++++++++++++++++++++++++++++-
>>>>> 1 file changed, 30 insertions(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/net/openvswitch/conntrack.c b/net/openvswitch/conntrack.c
>>>>> index 7b2c2fc..d796ae7 100644
>>>>> --- a/net/openvswitch/conntrack.c
>>>>> +++ b/net/openvswitch/conntrack.c
>>>>> @@ -514,10 +514,39 @@ ovs_ct_expect_find(struct net *net, const struct nf_conntrack_zone *zone,
>>>>> u16 proto, const struct sk_buff *skb)
>>>>> {
>>>>> struct nf_conntrack_tuple tuple;
>>>>> + struct nf_conntrack_expect *exp;
>>>>>
>>>>> if (!nf_ct_get_tuplepr(skb, skb_network_offset(skb), proto, net, &tuple))
>>>>> return NULL;
>>>>> - return __nf_ct_expect_find(net, zone, &tuple);
>>>>> +
>>>>> + exp = __nf_ct_expect_find(net, zone, &tuple);
>>>>> +
>>>>
>>>> Extraneous whitespace^
>>>>
>>>
>>> You mean the empty line?
>>
>> Yeah.
>
> I can remove this here before applying if that is fine to you, so you
> don't need to resubmit.
>
Yes, fine by me! Thank you!
Jarno
>>>>> + if (exp) {
>>>>> + struct nf_conntrack_tuple_hash *h;
>>>>> +
>>>>> + /* Delete existing conntrack entry, if it clashes with the
>>>>> + * expectation. This can happen since conntrack ALGs do not
>>>>> + * check for clashes between (new) expectations and existing
>>>>> + * conntrack entries. nf_conntrack_in() will check the
>>>>> + * expectations only if a conntrack entry can not be found,
>>>>> + * which can lead to OVS finding the expectation (here) in the
>>>>> + * init direction, but which will not be removed by the
>>>>> + * nf_conntrack_in() call, if a matching conntrack entry is
>>>>> + * found instead. In this case all init direction packets
>>>>> + * would be reported as new related packets, while reply
>>>>> + * direction packets would be reported as un-related
>>>>> + * established packets. */
>>>>> +
>>>>
>>>> Extraneous whitespace^
>
> We're converging to netdev comment style, ie.
>
> * ...
> * established packets.
> */
>
> I know we have a bunch of comments in netfilter ending like the one
> above, but ideally it would be good to use this comment style.
>
>>>>
>>>>> + h = nf_conntrack_find_get(net, zone, &tuple);
>>>>> + if (h) {
>>>>> + struct nf_conn *ct = nf_ct_tuplehash_to_ctrack(h);
>>>>> +
>>>>> + nf_ct_delete(ct, 0, 0);
>>>>> + nf_conntrack_put(&ct->ct_general);
>>>>
>>>> Do we need the extra nf_conntrack_put() here? If
>>>> nf_conntrack_find_get() returns an entry, we'll call nf_ct_delete()
>>>> which releases a reference on the CT entry.
>>>
>>> There is one reference held by the table, but nf_conntrack_find_get() takes another. nf_ct_delete() releases the reference held by the table as the entry is removed, but we need to explicitly release the reference taken by nf_conntrack_find_get().
>>
>> Ah, makes sense.
>>
>> Acked-by: Joe Stringer <joe@xxxxxxx>
>>
>> Did you intend for Pablo to take this? Pablo, is this fine or should
>> Jarno resubmit against net?
>
> I can take this, yes.
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