[ovs-dev] [ovs-discuss] a question about ovs crash relationship with learn action

[wangyunjian]

I think the function xlate_cache_clear() needs be called after xlate_push_stats() to
avoid xcache->entries use-after-free.

diff --git a/ofproto/ofproto-dpif-upcall.c b/ofproto/ofproto-dpif-upcall.c
index 85f5792..71b846c 100644
--- a/ofproto/ofproto-dpif-upcall.c
+++ b/ofproto/ofproto-dpif-upcall.c
@@ -2252,6 +2252,7 @@ revalidate_ukey(struct udpif *udpif, struct udpif_key *ukey,
     /* Stats for deleted flows will be attributed upon flow deletion. Skip. */
     if (result != UKEY_DELETE) {
         xlate_push_stats(ukey->xcache, &push);
+        xlate_cache_clear(ukey->xcache);
         ukey->stats = *stats;
         ukey->reval_seq = reval_seq;
     }

> From: wangyunjian 
> Sent: Monday, June 25, 2018 2:19 PM
> To: ovs-discuss at openvswitch.org
> Cc: 'blp at ovn.org' <blp at ovn.org>; Lilijun (Jerry, Cloud Networking) <jerry.lilijun at huawei.com>
> Subject: [ovs-discuss] a question about ovs crash relationship with learn action
> 
> I'm running OVS 2.7.0 on a Linux 3.10.0 kernel. I found a ovs crash.
> I doubt it's caused by use-after-free set match->flow = NULL in
> minimatch_destroy function with following stack:
> 
> (gdb) bt
> #0  0x00007ff273b71197 in raise () from /usr/lib64/libc.so.6
> #1  0x00007ff273b72888 in abort () from /usr/lib64/libc.so.6
> #2  0x0000000000787289 in PAT_abort ()
> #3  0x00000000007843cd in patchIllInsHandler ()
> #4  <signal handler called>
> #5  0x00000000004cbfae in miniflow_n_values (flow=0x0) at lib/flow.h:540
> #6  0x00000000004cc95f in minimask_hash (mask=0x0, basis=0) at lib/classifier-private.h:321
> #7  0x00000000004cf613 in find_subtable (cls=0x38ad6e8, mask=0x0) at lib/classifier.c:1406
> #8  0x00000000004cefa7 in classifier_find_rule_exactly (cls=0x38ad6e8, target=0x7ff118025500, version=18446744073709551615) at lib/classifier.c:1178
> #9  0x000000000047bcaf in collect_rules_strict (ofproto=0x389bc30, criteria=0x7ff1180254f8, rules=0x7ff118025588) at ofproto/ofproto.c:4253
> #10 0x000000000047eba3 in modify_flow_start_strict (ofproto=0x389bc30, ofm=0x7ff1180254f0) at ofproto/ofproto.c:5492
> #11 0x0000000000482c9f in ofproto_flow_mod_start (ofproto=0x389bc30, ofm=0x7ff1180254f0) at ofproto/ofproto.c:7506
> #12 0x000000000047dc01 in ofproto_flow_mod_learn_start (ofm=0x7ff1180254f0) at ofproto/ofproto.c:5088
> #13 0x000000000047dd4b in ofproto_flow_mod_learn (ofm=0x7ff1180254f0, keep_ref=true) at ofproto/ofproto.c:5140
> #14 0x00000000004b55d4 in xlate_push_stats_entry (entry=0x7ff118015148, stats=0x7ff11d6675f0) at ofproto/ofproto-dpif-xlate-cache.c:130
> #15 0x00000000004b57b6 in xlate_push_stats (xcache=0x7ff1180254a0, stats=0x7ff11d6675f0) at ofproto/ofproto-dpif-xlate-cache.c:183
> #16 0x00000000004a312f in revalidate_ukey (udpif=0x38a5260, ukey=0x7ff0fc015910, stats=0x7ff11d668260, odp_actions=0x7ff11d66a3d0, reval_seq=25145760, recircs=0x7ff11d66a3b0) at ofproto/ofproto-dpif-upcall.c:2134
> #17 0x00000000004a3d76 in revalidate (revalidator=0x4cdda08) at ofproto/ofproto-dpif-upcall.c:2428
> #18 0x00000000004a0528 in udpif_revalidator (arg=0x4cdda08) at ofproto/ofproto-dpif-upcall.c:954
> #19 0x000000000058f811 in ovsthread_wrapper (aux_=0x55088a0) at lib/ovs-thread.c:682
> #20 0x00007ff27549adc5 in start_thread () from /usr/lib64/libpthread.so.0
> 
> Any idea about this? 
> Thanks,
> Yunjian