On 6 Jul 2023, at 4:32, Peng He wrote:
> Eelco Chaudron <echau...@redhat.com> 于2023年7月5日周三 22:16写道：
>
>>
>>
>> On 1 Jul 2023, at 4:43, Peng He wrote:
>>
>>> OVS allows overlapping megaflows, as long as the actions of these
>>> megaflows are equal. However, the current implementation of action
>>> modification relies on flow_lookup instead of ufid, this could result
>>> in looking up a wrong megaflow and make the ukeys and megaflows
>> inconsistent
>>>
>>> Just like the test case in the patch, at first we have a rule with the
>>> prefix:
>>>
>>> 10.1.2.0/24
>>>
>>> and we will get a megaflow with prefixes 10.1.2.2/24 when a packet with
>> IP
>>> 10.1.2.2 is received.
>>>
>>> Then suppose we change the rule into 10.1.0.0/16. OVS prefers to keep
>> the
>>> 10.1.2.2/24 megaflow and just changes its action instead of extending
>>> the prefix into 10.1.2.2/16.
>>>
>>> then suppose we have a 10.1.0.2 packet, since it misses the megaflow,
>>> this time, we will have an overlapping megaflow with the right prefix:
>>> 10.1.0.2/16
>>>
>>> now we have two megaflows:
>>> 10.1.2.2/24
>>> 10.1.0.2/16
>>>
>>> last, suppose we have changed the ruleset again. The revalidator this
>>> time still decides to change the actions of both megaflows instead of
>>> deleting them.
>>>
>>> The dpif_netdev_flow_put will search the megaflow to modify with unmasked
>>> keys, however it might lookup the wrong megaflow as the key 10.1.2.2
>> matches
>>> both 10.1.2.2/24 and 10.1.0.2/16!
>>>
>>> This patch changes the megaflow lookup code in modification path into
>>> relying the ufid to find the correct megaflow instead of key lookup.
>>
>> Thanks for fixing Ilya’s comments! I’ve also copied in some of the v3
>> discussion, so we can wrap it up here.
>>
>> Acked-by: Eelco Chaudron <echau...@redhat.com>
>>
>> //Eelco
>>
>>> Signed-off-by: Peng He <hepeng.0...@bytedance.com>
>>> ---
>>> lib/dpif-netdev.c | 62 ++++++++++++++++++++++++++---------------------
>>> tests/pmd.at | 48 ++++++++++++++++++++++++++++++++++++
>>> 2 files changed, 82 insertions(+), 28 deletions(-)
>>>
>>> diff --git a/lib/dpif-netdev.c b/lib/dpif-netdev.c
>>> index 70b953ae6..b90ed1542 100644
>>> --- a/lib/dpif-netdev.c
>>> +++ b/lib/dpif-netdev.c
>>> @@ -4198,36 +4198,43 @@ flow_put_on_pmd(struct dp_netdev_pmd_thread *pmd,
>>> memset(stats, 0, sizeof *stats);
>>> }
>>>
>>> - ovs_mutex_lock(&pmd->flow_mutex);
>>> - netdev_flow = dp_netdev_pmd_lookup_flow(pmd, key, NULL);
>>> - if (!netdev_flow) {
>>> - if (put->flags & DPIF_FP_CREATE) {
>>> + if (put->flags & DPIF_FP_CREATE) {
>>
>>
>> EC> Should this not be:
>> EC>
>> EC> if (put->flags & DPIF_FP_CREATE && !(put->flags & DPIF_FP_MODIFY))
>> EC>
>> EC> I know this will break the fix, but I’m wondering what the possible
>> EC> combinations are.
>> EC> Quickly looking at the code the following ones seem to exist:
>> EC>
>> EC> DPIF_FP_CREATE -> Create a flow, if one exists return EEXIST
>> EC> DPIF_FP_MODIFY -> Modify a flow, if it does not exist return ENONT
>> EC> DPIF_FP_CREATE | DPIF_FP_MODIFY -> If it exists modify it, if it does
>> EC> not exists create it.
>> EC>
>> EC> Could the last combination not potentially fail the lookup?
>> EC>
>> EC> Or are we assuming only standalone DPIF_FP_MODIFY’s are the problem? In
>> EC> theory, it could also be the combination.
>> EC>
>>
>> PH> sorry, I was wrong. Such a combination does exist in
>> PH>the dpif_probe_feature, and it probes the datapath by trying to put
>> flows:
>> PH>
>> PH> error = dpif_flow_put(dpif, DPIF_FP_CREATE | DPIF_FP_MODIFY |
>> PH>DPIF_FP_PROBE,
>> PH> key->data, key->size, NULL, 0,
>> PH> nl_actions, nl_actions_size,
>> PH> ufid, NON_PMD_CORE_ID, NULL);
>>
>> PH> so we CANNOT change the code into:
>>
>> PH> if (put->flags & DPIF_FP_CREATE && !(put->flags & DPIF_FP_MODIFY))
>>
>> PH> as the issue the patch tries to fix only exist in MODIFY alone path.
>> PH> If CREATE bit is set, we need to go through the CREATE path no matter
>> if
>> PH> MODIFY exist or not.
>>
>> Ok, if this is only used by the probe function we should be fine. I did
>> quickly search the code and it seems to be the way. However, if it’s ever
>> used by any part of ovs with both flags set, it might fail the lookup and
>> we run into the same problem.
>>
>
> By "the same problem", you mean the problem listed in this patch or this
> fix might lead to a potential failure in other part of OVS?
If you have a request with both DPIF_FP_MODIFY and DPIF_FP_CREATE set, the
lookup could still return the wrong entry. But if this is not used it should be
fine for now.
>
>>
>>> + ovs_mutex_lock(&pmd->flow_mutex);
>>> + netdev_flow = dp_netdev_pmd_lookup_flow(pmd, key, NULL);
>>> + if (!netdev_flow) {
>>> dp_netdev_flow_add(pmd, match, ufid, put->actions,
>>> put->actions_len, ODPP_NONE);
>>> } else {
>>> - error = ENOENT;
>>> + error = EEXIST;
>>> }
>>> + ovs_mutex_unlock(&pmd->flow_mutex);
>>> } else {
>>> + netdev_flow = dp_netdev_pmd_find_flow(pmd, ufid,
>>> + put->key, put->key_len);
>>> +
>>> if (put->flags & DPIF_FP_MODIFY) {
>>> - struct dp_netdev_actions *new_actions;
>>> - struct dp_netdev_actions *old_actions;
>>> + if (!netdev_flow) {
>>> + error = ENOENT;
>>> + } else {
>>> + struct dp_netdev_actions *new_actions;
>>> + struct dp_netdev_actions *old_actions;
>>>
>>> - new_actions = dp_netdev_actions_create(put->actions,
>>> - put->actions_len);
>>> + new_actions = dp_netdev_actions_create(put->actions,
>>> +
>> put->actions_len);
>>>
>>> - old_actions = dp_netdev_flow_get_actions(netdev_flow);
>>> - ovsrcu_set(&netdev_flow->actions, new_actions);
>>> + old_actions = dp_netdev_flow_get_actions(netdev_flow);
>>> + ovsrcu_set(&netdev_flow->actions, new_actions);
>>>
>>> - queue_netdev_flow_put(pmd, netdev_flow, match,
>>> - put->actions, put->actions_len,
>>> - DP_NETDEV_FLOW_OFFLOAD_OP_MOD);
>>> - log_netdev_flow_change(netdev_flow, match, old_actions,
>>> - put->actions, put->actions_len);
>>> + queue_netdev_flow_put(pmd, netdev_flow, match,
>>> + put->actions, put->actions_len,
>>> + DP_NETDEV_FLOW_OFFLOAD_OP_MOD);
>>> + log_netdev_flow_change(netdev_flow, match, old_actions,
>>> + put->actions, put->actions_len);
>>>
>>> - if (stats) {
>>> - get_dpif_flow_status(pmd->dp, netdev_flow, stats, NULL);
>>> - }
>>> - if (put->flags & DPIF_FP_ZERO_STATS) {
>>> + if (stats) {
>>> + get_dpif_flow_status(pmd->dp, netdev_flow, stats,
>> NULL);
>>> + }
>>> + if (put->flags & DPIF_FP_ZERO_STATS) {
>>> /* XXX: The userspace datapath uses thread local
>> statistics
>>> * (for flows), which should be updated only by the
>> owning
>>> * thread. Since we cannot write on stats memory here,
>>> @@ -4237,18 +4244,17 @@ flow_put_on_pmd(struct dp_netdev_pmd_thread *pmd,
>>> * - Should the need arise, this operation can be
>> implemented
>>> * by keeping a base value (to be update here) for
>> each
>>> * counter, and subtracting it before outputting the
>> stats */
>>> - error = EOPNOTSUPP;
>>> + error = EOPNOTSUPP;
>>> + }
>>> + ovsrcu_postpone(dp_netdev_actions_free, old_actions);
>>> }
>>> -
>>> - ovsrcu_postpone(dp_netdev_actions_free, old_actions);
>>> - } else if (put->flags & DPIF_FP_CREATE) {
>>> - error = EEXIST;
>>> } else {
>>> - /* Overlapping flow. */
>>> - error = EINVAL;
>>> + if (netdev_flow) {
>>> + /* Overlapping flow. */
>>> + error = EINVAL;
>>> + }
>>> }
>>> }
>>> - ovs_mutex_unlock(&pmd->flow_mutex);
>>> return error;
>>> }
>>>
>>> diff --git a/tests/pmd.at b/tests/pmd.at
>>> index 48f3d432d..85211a30f 100644
>>> --- a/tests/pmd.at
>>> +++ b/tests/pmd.at
>>> @@ -1300,3 +1300,51 @@ OVS_WAIT_UNTIL([tail -n +$LINENUM
>> ovs-vswitchd.log | grep "PMD load based sleeps
>>>
>>> OVS_VSWITCHD_STOP
>>> AT_CLEANUP
>>> +
>>> +AT_SETUP([PMD - revalidator wrongly modify userspace megaflows])
>>> +
>>> +OVS_VSWITCHD_START(
>>> +[add-port br0 p1 \
>>> + -- set interface p1 type=dummy-pmd \
>>> + -- set bridge br0 datapath-type=dummy \
>>> + -- add-port br0 p2 \
>>> + -- set interface p2 type=dummy-pmd --
>>> +])
>>> +
>>> +dnl Add one openflow rule and generate a megaflow.
>>> +AT_CHECK([ovs-ofctl add-flow br0 'table=0,in_port=p1,ip,nw_dst=
>> 10.1.2.0/24,actions=p2'])
>>> +AT_CHECK([ovs-appctl netdev-dummy/receive p1
>> 'ipv4(src=10.0.0.1,dst=10.1.2.2),tcp(src=1,dst=2)'])
>>> +
>>> +AT_CHECK([ovs-appctl dpctl/dump-flows | sed 's/.*core: [[0-9]]*//'],
>> [0], [
>>>
>> +recirc_id(0),in_port(1),packet_type(ns=0,id=0),eth_type(0x0800),ipv4(dst=
>> 10.1.2.2/255.255.255.0,frag=no), packets:0, bytes:0, used:never, actions:2
>>> +])
>>> +
>>> +AT_CHECK([ovs-appctl netdev-dummy/receive p1
>> 'ipv4(src=10.0.0.1,dst=10.1.2.2),tcp(src=1,dst=2)'])
>>> +dnl Replace openflow rules, trigger the revalidation.
>>> +AT_CHECK([echo 'table=0,in_port=p1,ip,nw_dst=10.1.0.0/16
>> actions=ct(commit)' | dnl
>>> +ovs-ofctl --bundle replace-flows br0 -])
>>> +AT_CHECK([ovs-appctl revalidator/wait])
>>> +
>>> +AT_CHECK([ovs-appctl netdev-dummy/receive p1
>> 'ipv4(src=10.0.0.1,dst=10.1.0.2),tcp(src=1,dst=2)'])
>>> +AT_CHECK([ovs-appctl dpctl/dump-flows | sed 's/.*core: [[0-9]]*//' |
>> strip_xout_keep_actions], [0], [
>>>
>> +recirc_id(0),in_port(1),packet_type(ns=0,id=0),eth_type(0x0800),ipv4(dst=
>> 10.1.0.2/255.255.0.0,frag=no), packets:0, bytes:0, used:never,
>> actions:ct(commit)
>>>
>> +recirc_id(0),in_port(1),packet_type(ns=0,id=0),eth_type(0x0800),ipv4(dst=
>> 10.1.2.2/255.255.255.0,frag=no), packets:0, bytes:0, used:0.0s,
>> actions:ct(commit)
>>> +])
>>> +
>>> +dnl Hold the prefix 10.1.2.2/24 by another 10s.
>>> +AT_CHECK([ovs-appctl netdev-dummy/receive p1
>> 'ipv4(src=10.0.0.1,dst=10.1.2.2),tcp(src=1,dst=2)'])
>>> +dnl Send more 10.1.0.2 to make 10.1.0.0/16 tuple preprend 10.1.2.0/24
>> tuple in pvector of subtable.
>>> +for i in `seq 0 256`;do
>>> +AT_CHECK([ovs-appctl netdev-dummy/receive p1
>> 'ipv4(src=10.0.0.1,dst=10.1.0.2),tcp(src=1,dst=2)'])
>>> +done
>>> +
>>> +AT_CHECK([echo 'table=0,in_port=p1,ip,nw_dst=10.1.0.0/16 actions=p2' |
>> dnl
>>> +ovs-ofctl --bundle replace-flows br0 -])
>>> +
>>> +AT_CHECK([ovs-appctl dpctl/dump-flows | sed 's/.*core: [[0-9]]*//' |
>> strip_xout_keep_actions], [0], [
>>>
>> +recirc_id(0),in_port(1),packet_type(ns=0,id=0),eth_type(0x0800),ipv4(dst=
>> 10.1.0.2/255.255.0.0,frag=no), packets:0, bytes:0, used:0.0s, actions:2
>>>
>> +recirc_id(0),in_port(1),packet_type(ns=0,id=0),eth_type(0x0800),ipv4(dst=
>> 10.1.2.2/255.255.255.0,frag=no), packets:0, bytes:0, used:0.0s, actions:2
>>> +])
>>> +
>>> +OVS_VSWITCHD_STOP
>>> +AT_CLEANUP
>>> --
>>> 2.25.1
>>
>>
>
> --
> hepeng
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