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Date: Tue, 7 Feb 2017 21:31:24 -0800
From: Jarno Rajahalme <jarno@....org>
To: Joe Stringer <joe@....org>
Cc: netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next 6/7] openvswitch: Add force commit.
> On Feb 7, 2017, at 2:15 PM, Joe Stringer <joe@....org> wrote:
>
> On 2 February 2017 at 17:10, Jarno Rajahalme <jarno@....org> wrote:
>> Stateful network admission policy may allow connections to one
>> direction and reject connections initiated in the other direction.
>> After policy change it is possible that for a new connection an
>> overlapping conntrack entry already exist, where the connection
>> original direction is opposed to the new connection's initial packet.
>>
>> Most importantly, conntrack state relating to the current packet gets
>> the "reply" designation based on whether the original direction tuple
>> or the reply direction tuple matched. If this "directionality" is
>> wrong w.r.t. to the stateful network admission policy it may happen
>> that packets in neither direction are correctly admitted.
>>
>> This patch adds a new "force commit" option to the OVS conntrack
>> action that checks the original direction of an existing conntrack
>> entry. If that direction is opposed to the current packet, the
>> existing conntrack entry is deleted and a new one is subsequently
>> created in the correct direction.
>>
>> Signed-off-by: Jarno Rajahalme <jarno@....org>
>> ---
>> include/uapi/linux/openvswitch.h | 10 ++++++++++
>> net/openvswitch/conntrack.c | 27 +++++++++++++++++++++++++--
>> 2 files changed, 35 insertions(+), 2 deletions(-)
>>
>> diff --git a/include/uapi/linux/openvswitch.h b/include/uapi/linux/openvswitch.h
>> index 90af8b8..d5ba9a9 100644
>> --- a/include/uapi/linux/openvswitch.h
>> +++ b/include/uapi/linux/openvswitch.h
>> @@ -674,6 +674,10 @@ struct ovs_action_hash {
>> * @OVS_CT_ATTR_HELPER: variable length string defining conntrack ALG.
>> * @OVS_CT_ATTR_NAT: Nested OVS_NAT_ATTR_* for performing L3 network address
>> * translation (NAT) on the packet.
>> + * @OVS_CT_ATTR_FORCE_COMMIT: Like %OVS_CT_ATTR_COMMIT, but instead of doing
>> + * nothing if the connection is already committed will check that the current
>> + * packet is in conntrack entry's original direction. If directionality does
>> + * not match, will delete the existing conntrack entry and commit a new one.
>> */
>> enum ovs_ct_attr {
>> OVS_CT_ATTR_UNSPEC,
>> @@ -684,6 +688,12 @@ enum ovs_ct_attr {
>> OVS_CT_ATTR_HELPER, /* netlink helper to assist detection of
>> related connections. */
>> OVS_CT_ATTR_NAT, /* Nested OVS_NAT_ATTR_* */
>> + OVS_CT_ATTR_FORCE_COMMIT, /* No argument, commits connection. If the
>> + * conntrack entry original direction tuple
>> + * does not match the current packet header
>> + * values, will delete the current conntrack
>> + * entry and create a new one.
>> + */
>
> We only need one copy of the explanation, keep it above the enum, then
> the inline comment can be /* No argument */.
>
OK.
>> __OVS_CT_ATTR_MAX
>> };
>>
>> diff --git a/net/openvswitch/conntrack.c b/net/openvswitch/conntrack.c
>> index 1afe153..1f27f44 100644
>> --- a/net/openvswitch/conntrack.c
>> +++ b/net/openvswitch/conntrack.c
>> @@ -65,6 +65,7 @@ struct ovs_conntrack_info {
>> struct nf_conn *ct;
>> u8 commit : 1;
>> u8 nat : 3; /* enum ovs_ct_nat */
>> + u8 force : 1;
>> u16 family;
>> struct md_mark mark;
>> struct md_labels labels;
>> @@ -631,10 +632,13 @@ static bool skb_nfct_cached(struct net *net,
>> */
>> if (!ct && key->ct.state & OVS_CS_F_TRACKED &&
>> !(key->ct.state & OVS_CS_F_INVALID) &&
>> - key->ct.zone == info->zone.id)
>> + key->ct.zone == info->zone.id) {
>> ct = ovs_ct_find_existing(net, &info->zone, info->family, skb,
>> !!(key->ct.state
>> & OVS_CS_F_NAT_MASK));
>> + if (ct)
>> + nf_ct_get(skb, &ctinfo);
>> + }
>
> If ctinfo is only used with the new call below, we can unconditionally
> fetch this just before it's used...
>
>> if (!ct)
>> return false;
>> if (!net_eq(net, read_pnet(&ct->ct_net)))
>> @@ -648,6 +652,19 @@ static bool skb_nfct_cached(struct net *net,
>> if (help && rcu_access_pointer(help->helper) != info->helper)
>> return false;
>> }
>> + /* Force conntrack entry direction to the current packet? */
>
> Here.
>
But then we would be executing nf_ct_get() twice in the common case?
>> + if (info->force && CTINFO2DIR(ctinfo) != IP_CT_DIR_ORIGINAL) {
>> + /* Delete the conntrack entry if confirmed, else just release
>> + * the reference.
>> + */
>> + if (nf_ct_is_confirmed(ct))
>> + nf_ct_delete(ct, 0, 0);
>> + else
>> + nf_ct_put(ct);
>
> We've already ensured that ct is non-NULL, we can use
> nf_conntrack_put() instead.
>
Right.
>> + skb->nfct = NULL;
>> + skb->nfctinfo = 0;
>> + return false;
>> + }
>>
>> return true;
>> }
>> @@ -1226,6 +1243,7 @@ static int parse_nat(const struct nlattr *attr,
>>
>> static const struct ovs_ct_len_tbl ovs_ct_attr_lens[OVS_CT_ATTR_MAX + 1] = {
>> [OVS_CT_ATTR_COMMIT] = { .minlen = 0, .maxlen = 0 },
>> + [OVS_CT_ATTR_FORCE_COMMIT] = { .minlen = 0, .maxlen = 0 },
>> [OVS_CT_ATTR_ZONE] = { .minlen = sizeof(u16),
>> .maxlen = sizeof(u16) },
>> [OVS_CT_ATTR_MARK] = { .minlen = sizeof(struct md_mark),
>> @@ -1265,6 +1283,9 @@ static int parse_ct(const struct nlattr *attr, struct ovs_conntrack_info *info,
>> }
>>
>> switch (type) {
>> + case OVS_CT_ATTR_FORCE_COMMIT:
>> + info->force = true;
>> + /* fall through. */
>> case OVS_CT_ATTR_COMMIT:
>> info->commit = true;
>> break;
>> @@ -1491,7 +1512,9 @@ int ovs_ct_action_to_attr(const struct ovs_conntrack_info *ct_info,
>> if (!start)
>> return -EMSGSIZE;
>>
>> - if (ct_info->commit && nla_put_flag(skb, OVS_CT_ATTR_COMMIT))
>> + if (ct_info->commit && nla_put_flag(skb, ct_info->force
>> + ? OVS_CT_ATTR_FORCE_COMMIT
>> + : OVS_CT_ATTR_COMMIT))
>> return -EMSGSIZE;
>> if (IS_ENABLED(CONFIG_NF_CONNTRACK_ZONES) &&
>> nla_put_u16(skb, OVS_CT_ATTR_ZONE, ct_info->zone.id))
>> --
>> 2.1.4
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