On 2/27/21 10:34 AM, Peng He wrote:
> CT zone could be set from a field that is not included in frozen
> metadata. Consider the example rules which are typically seen in
> OpenStack security group rules:
>
> priority=100,in_port=1,tcp,ct_state=-trk,action=ct(zone=5,table=0)
> priority=100,in_port=1,tcp,ct_state=+trk,action=ct(commit,zone=NXM_NX_CT_ZONE[]),2
>
> The zone is set from the first rule's ct action. These two rules will
> generate two megaflows: the first one uses zone=5 to query the CT module,
> the second one sets the zone-id from the first megaflow and commit to CT.
>
> The current implementation will generate a megaflow that does not use
> ct_zone=5 as a match, but directly commit into the ct using zone=5, as zone is
> set by an Imm not a field.
>
> Consider a situation that one changes the zone id (for example to 15)
> in the first rule, however, still keep the second rule unchanged. During
> this change, there is traffic hitting the two generated megaflows, the
> revaldiator would revalidate all megaflows, however, the revalidator will
> not change the second megaflow, because zone=5 is recorded in the
> megaflow, so the xlate will still translate the commit action into zone=5,
> and the new traffic will still commit to CT as zone=5, not zone=15,
> resulting in taffic drops and other issues.
>
> Just like OVS set-field convention, if a field X is set by Y
> (Y is a variable not an Imm), we should also mask Y as a match
> in the generated megaflow. An exception is that if the zone-id is
> set by the field that is included in the frozen state (i.e. regs) and this
> upcall is a resume of a thawed xlate, the un-wildcarding can be skipped,
> as the recirc_id is a hash of the values in these fields, and it will change
> following the changes of these fields. When the recirc_id changes,
> all megaflows with the old recirc id will be invalid later.
>
> Fixes: 07659514c3 ("Add support for connection tracking.")
> Reported-by: Sai Su <susai...@bytedance.com>
> Signed-off-by: Peng He <hepeng.0...@bytedance.com>
> ---
> include/openvswitch/meta-flow.h | 1 +
> lib/meta-flow.c | 13 ++++++++++
> ofproto/ofproto-dpif-xlate.c | 12 +++++++++
> tests/system-traffic.at | 45 +++++++++++++++++++++++++++++++++
> 4 files changed, 71 insertions(+)
>
> diff --git a/include/openvswitch/meta-flow.h b/include/openvswitch/meta-flow.h
> index 95e52e358..045dce8f5 100644
> --- a/include/openvswitch/meta-flow.h
> +++ b/include/openvswitch/meta-flow.h
> @@ -2305,6 +2305,7 @@ void mf_set_flow_value_masked(const struct mf_field *,
> const union mf_value *mask,
> struct flow *);
> bool mf_is_tun_metadata(const struct mf_field *);
> +bool mf_is_frozen_metadata(const struct mf_field *);
> bool mf_is_pipeline_field(const struct mf_field *);
> bool mf_is_set(const struct mf_field *, const struct flow *);
> void mf_mask_field(const struct mf_field *, struct flow_wildcards *);
> diff --git a/lib/meta-flow.c b/lib/meta-flow.c
> index c808d205d..e03cd8d0c 100644
> --- a/lib/meta-flow.c
> +++ b/lib/meta-flow.c
> @@ -1788,6 +1788,19 @@ mf_is_tun_metadata(const struct mf_field *mf)
> mf->id < MFF_TUN_METADATA0 + TUN_METADATA_NUM_OPTS;
> }
>
> +bool
> +mf_is_frozen_metadata(const struct mf_field *mf)
> +{
> + if (mf->id >= MFF_TUN_ID && mf->id <= MFF_IN_PORT_OXM) {
> + return true;
> + }
> +
> + if (mf->id >= MFF_REG0 && mf->id < MFF_ETH_SRC) {
> + return true;
> + }
> + return false;
> +}
> +
> bool
> mf_is_pipeline_field(const struct mf_field *mf)
> {
> diff --git a/ofproto/ofproto-dpif-xlate.c b/ofproto/ofproto-dpif-xlate.c
> index 7108c8a30..14d00db1e 100644
> --- a/ofproto/ofproto-dpif-xlate.c
> +++ b/ofproto/ofproto-dpif-xlate.c
> @@ -6195,6 +6195,18 @@ compose_conntrack_action(struct xlate_ctx *ctx, struct
> ofpact_conntrack *ofc,
>
> if (ofc->zone_src.field) {
> zone = mf_get_subfield(&ofc->zone_src, &ctx->xin->flow);
> + if (ctx->xin->frozen_state) {
> + /* If the upcall is a resume of a recirculation, we only need to
> + * unwildcard the fields that are not in the frozen_metadata, as
> + * when the rules update, OVS will generate a new recirc_id,
> + * which will invalidate the megaflow with old the recirc_id.
> + */
> + if (!mf_is_frozen_metadata(ofc->zone_src.field)) {
> + mf_mask_field(ofc->zone_src.field, ctx->wc);
> + }
> + } else {
> + mf_mask_field(ofc->zone_src.field, ctx->wc);
> + }
IIUC, in current code above block is equal to just a single line:
mf_mask_field(ofc->zone_src.field, ctx->wc);
That is because zone is not part of a frozen metadata, right?
Can we just remove all this extra logic and unwildcard unconditionally?
I understand that this code might save us one match in case someday
zone will be part of a frozen metadata, but is that really important?
Is there any harm in unwildcarding this field unconditionally?
Best regards, Ilya Maximets.
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