If packet headers changed, the cached nfct is no longer relevant for the packet and attempt to re-use it leads to the incorrect packet classification.

This issue is causing broken connectivity in OpenStack deployments with OVS/OVN due to hairpin traffic being unexpectedly dropped.

The setup has datapath flows with several conntrack actions and tuple changes between them:

actions:ct(commit,zone=8,mark=0/0x1,nat(src)), set(eth(src=00:00:00:00:00:01,dst=00:00:00:00:00:06)), set(ipv4(src=172.18.2.10,dst=192.168.100.6,ttl=62)), ct(zone=8),recirc(0x4)

After the first ct() action the packet headers are almost fully re-written. The next ct() tries to re-use the existing nfct entry and marks the packet as invalid, so it gets dropped later in the pipeline.

Clearing the cached conntrack entry whenever packet tuple is changed to avoid the issue.

The flow key should not be cleared though, because we should still be able to match on the ct_state if the recirculation happens after the tuple change but before the next ct() action.

Cc: stable@vger.kernel.org Fixes: 7f8a436eaa2c ("openvswitch: Add conntrack action") Reported-by: Frode Nordahl frode.nordahl@canonical.com Link: https://mail.openvswitch.org/pipermail/ovs-discuss/2022-May/051829.html Link: https://bugs.launchpad.net/ubuntu/+source/ovn/+bug/1967856 Signed-off-by: Ilya Maximets i.maximets@ovn.org ---

The function ovs_ct_clear() looks a bit differently on older branches, but the change should be exactly the same, i.e. move the ovs_ct_fill_key() under the 'if (key)'.

The same behavior for userspace datapath was introduced along with the conntrack caching support here: https://github.com/openvswitch/ovs/commit/594570ea1cdecc7ef7880d707cbc7a4a4e...

Interestingly, above commit also introduced the system test that can check the issue for the kernel as well, but the test sends only one packet and this packet goes via upcall to userspace and back to the kernel effectively clearing the cached connection along the way and avoiding the issue. If the test is modified to send more than a few packets [1], it starts to fail without the kernel fix:

make check-kernel TESTSUITEFLAGS='-k negative' 142: conntrack - negative test for recirculation optimization FAILED

[1] https://pastebin.com/H1YMqaLa

net/openvswitch/actions.c | 6 ++++++ net/openvswitch/conntrack.c | 4 +++- 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/net/openvswitch/actions.c b/net/openvswitch/actions.c index 1b5d73079dc9..868db4669a29 100644 --- a/net/openvswitch/actions.c +++ b/net/openvswitch/actions.c @@ -373,6 +373,7 @@ static void set_ip_addr(struct sk_buff *skb, struct iphdr *nh, update_ip_l4_checksum(skb, nh, *addr, new_addr); csum_replace4(&nh->check, *addr, new_addr); skb_clear_hash(skb); + ovs_ct_clear(skb, NULL); *addr = new_addr; }

@@ -420,6 +421,7 @@ static void set_ipv6_addr(struct sk_buff *skb, u8 l4_proto, update_ipv6_checksum(skb, l4_proto, addr, new_addr);

skb_clear_hash(skb); + ovs_ct_clear(skb, NULL); memcpy(addr, new_addr, sizeof(__be32[4])); }

@@ -660,6 +662,7 @@ static int set_nsh(struct sk_buff *skb, struct sw_flow_key *flow_key, static void set_tp_port(struct sk_buff *skb, __be16 *port, __be16 new_port, __sum16 *check) { + ovs_ct_clear(skb, NULL); inet_proto_csum_replace2(check, skb, *port, new_port, false); *port = new_port; } @@ -699,6 +702,7 @@ static int set_udp(struct sk_buff *skb, struct sw_flow_key *flow_key, uh->dest = dst; flow_key->tp.src = src; flow_key->tp.dst = dst; + ovs_ct_clear(skb, NULL); }

skb_clear_hash(skb); @@ -761,6 +765,8 @@ static int set_sctp(struct sk_buff *skb, struct sw_flow_key *flow_key, sh->checksum = old_csum ^ old_correct_csum ^ new_csum;

skb_clear_hash(skb); + ovs_ct_clear(skb, NULL); + flow_key->tp.src = sh->source; flow_key->tp.dst = sh->dest;

diff --git a/net/openvswitch/conntrack.c b/net/openvswitch/conntrack.c index 4a947c13c813..4e70df91d0f2 100644 --- a/net/openvswitch/conntrack.c +++ b/net/openvswitch/conntrack.c @@ -1342,7 +1342,9 @@ int ovs_ct_clear(struct sk_buff *skb, struct sw_flow_key *key)

nf_ct_put(ct); nf_ct_set(skb, NULL, IP_CT_UNTRACKED); - ovs_ct_fill_key(skb, key, false); + + if (key) + ovs_ct_fill_key(skb, key, false);

return 0; }