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. > > 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. > >> 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
