On 6/9/21 3:12 PM, Aaron Conole wrote: > Ilya Maximets <[email protected]> writes: > >> On 6/7/21 3:59 PM, Ilya Maximets wrote: >>> On 6/7/21 3:09 PM, Aaron Conole wrote: >>>> Ilya Maximets <[email protected]> writes: >>>> >>>>>> Here is a patch with both a test and a fix. >>>> >>>> Thanks so much! It's nice to get fixes, but I think it's really great >>>> when test cases come along with them. >>>> >>>>> Hi. Thanks for working n this! >>>>> >>>>> CC: ovs-dev >>>>> >>>>>> Not submitting as a formal >>>>>> patch because I would like some feedback on whether 1) maintainers feel >>>>>> this is worth fixing and >>>>> >>>>> I can reproduce the crash with your test. Basically, actions in userspace >>>>> datapath may drop packets if something goes wrong. 'meter' action just >>>>> seems to be the most explicit variant. So, I think, this is definitely >>>>> worth fixing as some other condition might trigger this crash on >>>>> packet-out >>>>> as well. >>>>> >>>>> ==2568112==ERROR: AddressSanitizer: heap-use-after-free >>>>> on address 0x61600000699c at pc 0x000000573860 bp 0x7ffebc6cc880 sp >>>>> 0x7ffebc6cc878 >>>>> READ of size 1 at 0x61600000699c thread T0 >>>>> #0 0x57385f in dp_packet_delete lib/dp-packet.h:242:16 >>>>> #1 0x57372c in ofproto_packet_out_uninit ofproto/ofproto.c:3562:5 >>>>> #2 0x585e77 in handle_packet_out ofproto/ofproto.c:3722:5 >>>>> #3 0x583801 in handle_single_part_openflow ofproto/ofproto.c:8499:16 >>>>> #4 0x570c9c in handle_openflow ofproto/ofproto.c:8686:21 >>>>> #5 0x611781 in ofconn_run ofproto/connmgr.c:1329:13 >>>>> #6 0x6112ed in connmgr_run ofproto/connmgr.c:356:9 >>>>> #7 0x56fdf4 in ofproto_run ofproto/ofproto.c:1891:5 >>>>> #8 0x545ec0 in bridge_run__ vswitchd/bridge.c:3251:9 >>>>> #9 0x5456a5 in bridge_run vswitchd/bridge.c:3310:5 >>>>> #10 0x55f5b1 in main vswitchd/ovs-vswitchd.c:127:9 >>>>> #11 0x7f85bfe09081 in __libc_start_main (/lib64/libc.so.6+0x27081) >>>>> #12 0x46d00d in _start (vswitchd/ovs-vswitchd+0x46d00d) >>>>> >>>>>> 2) whether this is the way to fix it. >>>>> >>>>> See inline. >>>>> >>>>>> >>>>>> I have tried to make the most minimal change possible, but this means >>>>>> that >>>>>> there might be paths through the code that give unexpected behaviour >>>>>> (which >>>>>> in the worst case would be a memory leak I suppose). >>>>>> >>>>>> Tony >>>>>> >>>>>> diff --git a/lib/dp-packet.h b/lib/dp-packet.h >>>>>> index 246be14d0..5e0dabe67 100644 >>>>>> --- a/lib/dp-packet.h >>>>>> +++ b/lib/dp-packet.h >>>>>> @@ -739,6 +739,7 @@ struct dp_packet_batch { >>>>>> size_t count; >>>>>> bool trunc; /* true if the batch needs truncate. */ >>>>>> bool do_not_steal; /* Indicate that the packets should not be stolen. >>>>>> */ >>>>>> + bool packet_out; /* Indicate single packet is PACKET_OUT */ >>>>>> struct dp_packet *packets[NETDEV_MAX_BURST]; >>>>>> }; >>>>>> >>>>>> @@ -748,6 +749,7 @@ dp_packet_batch_init(struct dp_packet_batch *batch) >>>>>> batch->count = 0; >>>>>> batch->trunc = false; >>>>>> batch->do_not_steal = false; >>>>>> + batch->packet_out = false; >>>>>> } >>>>>> >>>>>> static inline void >>>>>> diff --git a/lib/dpif-netdev.c b/lib/dpif-netdev.c >>>>>> index 650e67ab3..deba4a94a 100644 >>>>>> --- a/lib/dpif-netdev.c >>>>>> +++ b/lib/dpif-netdev.c >>>>>> @@ -4170,6 +4170,7 @@ dpif_netdev_execute(struct dpif *dpif, struct >>>>>> dpif_execute *execute) >>>>>> >>>>>> dp_packet_batch_init_packet(&pp, execute->packet); >>>>>> pp.do_not_steal = true; >>>>>> + pp.packet_out = execute->packet_out; >>>>>> dp_netdev_execute_actions(pmd, &pp, false, execute->flow, >>>>>> execute->actions, execute->actions_len); >>>>> >>>>> There is already a dirty hack named "do_not_steal" that was introduced, >>>>> I guess, exactly to avoid crash in the conntrack code that could >>>>> drop/steal >>>>> the packet just like meter action. And it seems that here in >>>>> dpif_netdev_execute() is the only problematic entry point as all other >>>>> normal paths expects that packet might be destroyed. >>>>> >>>>> The problem was, I suppose, introduced when we tried to unify semantics >>>>> of "may_steal" flag by turning it into "should_steal". But it seems that >>>>> in this function we really need to prohibit stealing of the packet since >>>>> ofproto layer still owns it regardless of the result of execution. >>>>> >>>>> I don't think that we need one more flag here, but we have several options >>>>> how to fix the crash: >>>>> >>>>> 1. Start honoring batch->do_not_steal flag in all actions that may result >>>>> in packet drops. As the original idea of having 'do_not_steal' flag >>>>> for >>>>> a batch is very hacky, I'd like to not do that. >>>> >>>> +1 >>>> >>>>> 2. Try to propagate information that packet was deleted up to ofproto >>>>> layer, >>>>> i.e. make handle_packet_out() aware of that. Will, probably, be not >>>>> that >>>>> easy to do. >>>> >>>> I had a look at doing this, but as you note it is quite intrusive, and >>>> we need to make changes all over. >>>> >>>>> 3. This function (dpif_netdev_execute) is not on a hot path in userspace >>>>> datapath, IIUC. It might be that it's just easier to remove the >>>>> 'do_not_steal' flag entirely, clone the packet here and call the >>>>> dp_netdev_execute_actions() with should_steal=true. >>>>> This sounds like the best solution for me, unless I overlooked some >>>>> scenario, where this code is on a hot path. >>>> >>>> I like this approach. >>>> >>>>> Thoughts? >>>>> >>>>> Aaron, you have a patch[1] to remove 'do_not_steal' flag, so fix for this >>>>> issue >>>>> will, likely, touch the same parts of the code. What do you think about >>>>> this >>>>> issue and possible solutions? >>>> >>>> I guess we should do the same thing we do in other places, ie: default >>>> assume that the packet cannot be 'stolen' and we should clone our own >>>> copies. >>> >>> I'm not sure that I understood this correctly, but the idea was that default >>> assumption is that packet can be stolen at any point of datapath processing >>> and higher layers should deal with this. > > Re-reading what I wrote, I don't either. :-/ I agree with what you've > written. > >>> For the IP fragmentation handling this will mean that ipf will just take a >>> packet directly from the original batch without copying, so the original >>> batch will not have this packet anymore and ipf is allowed to free it at >>> any point in time, because now it owns this packet. >>> This aligns with the "should_steal" semantics, as any function called with >>> "should_steal=true" must take the ownership of the packet. If the function >>> called with "should_steal=false" it still allowed to take ownership of some >>> packets from the batch and caller must be prepared for that. >>> If some function in datapath has no "should_steal" argument, it should be >>> treated as a function with "should_steal=false". This applies to both >>> conntrack_execute() and dp_netdev_run_meter(), also to netdev_pop_header() >>> and so on. >> >> Hmm, OVS_ACTION_ATTR_TUNNEL_POP implies recirculation, so netdev_pop_header() >> is not a fully valid example here. Actions that implies recirculation or >> recirculates packets in any other way (e.g. OVS_ACTION_ATTR_USERSPACE) should >> clone packets before doing that if not asked to take ownership. > > The ownership of the dp_packet object needs to be well established. Use > of should_steal could be okay, but as an example, we have something in > the packet batch but it doesn't actually get honored (which is why I > proposed removing it).
Yeah. It looks like we have more issues than I thought initially. I thought that ip fragmentation module actually steals packets from the original batch, but it doesn't. Instead it tries to hack some poor form of reference counting with 'do_not_steal' flag. This also creates yet another logical difference with kernel conntrack implementation that actually steals fragments and therefore stops their processing until reassembled. In the end, I think we can't create a consolidated solution here for all problems at once. At least, we can't do that easily. So, what I will do is that I'll review and apply Aaron's fix for ipf: https://patchwork.ozlabs.org/project/openvswitch/patch/[email protected]/ And this bug with crash on packet_out with meters should be fixed by cloning the packet inside dpif_netdev_execute() and calling the dp_netdev_execute_actions() with should_steal=true. Tony, could you prepare a patch for this? Best regards, Ilya Maximets. > >>>> If we are worried about the time it takes to copy the dp_packet >>>> structure and buffer, we can always introduce a reference counting >>>> mechanism later as an optimization. >>>> >>>> I would just prefer to do clone, and then the functional area which >>>> needs to hold a reference to a valid packet buffer can delete when it >>>> makes sense. >>>> >>>> Hope it helps. >>>> >>>>> Best regards, Ilya Maximets. >>>>> >>>>> >>>>> [1] >>>>> https://patchwork.ozlabs.org/project/openvswitch/patch/[email protected]/ >>>>> >>>>> Non-line-wrapped version of the test for convenience: >>>>> >>>>> diff --git a/tests/ofproto-dpif.at b/tests/ofproto-dpif.at >>>>> index 31064ed95..d01f438b8 100644 >>>>> --- a/tests/ofproto-dpif.at >>>>> +++ b/tests/ofproto-dpif.at >>>>> @@ -2159,6 +2159,27 @@ meter:controller flow_count:0 packet_in_count:8 >>>>> byte_in_count:112 duration:0.0s >>>>> OVS_VSWITCHD_STOP >>>>> AT_CLEANUP >>>>> >>>>> +AT_SETUP([ofproto-dpif packet-out table meter drop qwe]) >>>>> +OVS_VSWITCHD_START >>>>> +add_of_ports br0 1 2 >>>>> + >>>>> +AT_CHECK([ovs-ofctl -O OpenFlow13 add-meter br0 'meter=1 pktps >>>>> bands=type=drop rate=1']) >>>>> +AT_CHECK([ovs-ofctl -O OpenFlow13 add-flow br0 'in_port=1 >>>>> action=meter:1,output:2']) >>>>> + >>>>> +ovs-ofctl -O OpenFlow13 packet-out br0 "in_port=1 >>>>> packet=50540000000a50540000000908004500001c000000000011a4cd0a0101010a0101020001000400080000 >>>>> actions=resubmit(,0)" >>>>> +ovs-ofctl -O OpenFlow13 packet-out br0 "in_port=1 >>>>> packet=50540000000a50540000000908004500001c000000000011a4cd0a0101010a0101020001000400080000 >>>>> actions=resubmit(,0)" >>>>> + >>>>> +# Check that vswitchd hasn't crashed by dumping the meter added above >>>>> +AT_CHECK([ovs-ofctl -O OpenFlow13 dump-meters br0 | ofctl_strip], [0], >>>>> [dnl >>>>> +OFPST_METER_CONFIG reply (OF1.3): >>>>> +meter=1 pktps bands= >>>>> +type=drop rate=1 >>>>> +]) >>>>> + >>>>> +OVS_VSWITCHD_STOP >>>>> +AT_CLEANUP >>>>> + >>>>> + >>>>> AT_SETUP([ofproto-dpif - MPLS handling]) >>>>> OVS_VSWITCHD_START([dnl >>>>> add-port br0 p1 -- set Interface p1 type=dummy >>>>> --- >>>> >>> > _______________________________________________ dev mailing list [email protected] https://mail.openvswitch.org/mailman/listinfo/ovs-dev
