> 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?
>> + 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^
>
>> + 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().
Jarno
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