[ovs-dev] [PATCHv2] connmgr: Check nullptr inside ofmonitor_report()

[Ilya Maximets]

On 2/19/21 3:12 AM, 贺鹏 wrote:
> Hi,
> 
> Looks like this bug is caused by violating the fact that if a rule is
> referenced, the related ofproto should not be destroyed.
> 
> If so, I have a patch that also fixes the problem, not sure if this helps.
> 
> http://patchwork.ozlabs.org/project/openvswitch/patch/20200717015041.82746-1-hepeng.0320@bytedance.com/

There is at least one more problem that is not strictly related but
in more or less the same part of the code:
  https://mail.openvswitch.org/pipermail/ovs-dev/2021-February/380582.html

> 
> William Tu <u9012063 at gmail.com> 于2021年2月19日周五 上午8:10写道：
>>
>> On Wed, Feb 17, 2021 at 1:09 PM Yifeng Sun <pkusunyifeng at gmail.com> wrote:
>>>
>>> ovs-vswitchd could crash under these circumstances:
>>> 1. When one bridge is being destroyed, ofproto_destroy() is called and
>>> connmgr pointer of its ofproto struct is nullified. This ofproto struct is
>>> deallocated through 'ovsrcu_postpone(ofproto_destroy_defer__, p);'.
>>> 2. Before RCU enters quiesce state to actually free this ofproto struct,
>>> revalidator thread calls udpif_revalidator(), which could handle
>>> a learn flow and calls ofproto_flow_mod_learn(), it later calls
>>> ofmonitor_report() and ofproto struct's connmgr pointer is accessed.
>>>
>>> The crash stack trace is shown below:
>>>
>>> 0  ofmonitor_report (mgr=0x0, rule=rule at entry=0x7fa4ac067c30, event=event at entry=NXFME_ADDED,
>>>     reason=reason at entry=OFPRR_IDLE_TIMEOUT, abbrev_ofconn=0x0, abbrev_xid=0, old_actions=old_actions at entry=0x0)
>>>     at ofproto/connmgr.c:2160
>>> 1  0x00007fa4d6803495 in add_flow_finish (ofproto=0x55d9075d4ab0, ofm=<optimized out>, req=req at entry=0x0)
>>>     at ofproto/ofproto.c:5221
>>> 2  0x00007fa4d68036af in modify_flows_finish (req=0x0, ofm=0x7fa4980753f0, ofproto=0x55d9075d4ab0)
>>>     at ofproto/ofproto.c:5823
>>> 3  ofproto_flow_mod_finish (ofproto=0x55d9075d4ab0, ofm=ofm at entry=0x7fa4980753f0, req=req at entry=0x0)
>>>     at ofproto/ofproto.c:8088
>>> 4  0x00007fa4d680372d in ofproto_flow_mod_learn_finish (ofm=ofm at entry=0x7fa4980753f0,
>>>     orig_ofproto=orig_ofproto at entry=0x0) at ofproto/ofproto.c:5439
>>> 5  0x00007fa4d68072f9 in ofproto_flow_mod_learn (ofm=0x7fa4980753f0, keep_ref=keep_ref at entry=true,
>>>     limit=<optimized out>, below_limitp=below_limitp at entry=0x0) at ofproto/ofproto.c:5499
>>> 6  0x00007fa4d6835d33 in xlate_push_stats_entry (entry=0x7fa498012448, stats=stats at entry=0x7fa4d2701a10,
>>>     offloaded=offloaded at entry=false) at ofproto/ofproto-dpif-xlate-cache.c:127
>>> 7  0x00007fa4d6835e3a in xlate_push_stats (xcache=<optimized out>, stats=stats at entry=0x7fa4d2701a10,
>>>     offloaded=offloaded at entry=false) at ofproto/ofproto-dpif-xlate-cache.c:181
>>> 8  0x00007fa4d6822046 in revalidate_ukey (udpif=udpif at entry=0x55d90760b240, ukey=ukey at entry=0x7fa4b0191660,
>>>     stats=stats at entry=0x7fa4d2705118, odp_actions=odp_actions at entry=0x7fa4d2701b50,
>>>     reval_seq=reval_seq at entry=5655486242, recircs=recircs at entry=0x7fa4d2701b40, offloaded=false)
>>>     at ofproto/ofproto-dpif-upcall.c:2294
>>> 9  0x00007fa4d6825aee in revalidate (revalidator=0x55d90769dd00) at ofproto/ofproto-dpif-upcall.c:2683
>>> 10 0x00007fa4d6825cf3 in udpif_revalidator (arg=0x55d90769dd00) at ofproto/ofproto-dpif-upcall.c:936
>>> 11 0x00007fa4d6259c9f in ovsthread_wrapper (aux_=<optimized out>) at lib/ovs-thread.c:423
>>> 12 0x00007fa4d582cea5 in start_thread () from /usr/lib64/libpthread.so.0
>>> 13 0x00007fa4d504b96d in clone () from /usr/lib64/libc.so.6
>>>
>>> At the time of crash, the involved ofproto was already deallocated:
>>>
>>> (gdb) print *ofproto
>>> $1 = ..., name = 0x55d907602820 "nsx-managed", ..., ports = {...,
>>>     one = 0x0, mask = 63, n = 0}, ..., connmgr = 0x0, ...
>>>
>>> This patch fixes it.
>>>
>>> VMware-BZ: #2700626
>>> Signed-off-by: Yifeng Sun <pkusunyifeng at gmail.com>
>>> ---
>>> v1->v2: Add check for ofmonitor_flush, thanks William.
>>>
>>
>> LGTM, thanks.
>> Acked-by: William Tu < u9012063 at gmail.com>
>>
>> CC Ilya and Ben to see if any comments.
>>
>> I feel this kind of RCU issue is hard to find out, and
>> existing tools such as addressSanitizer are usually
>> not helpful.
>>
>> William
>>
>>>  ofproto/connmgr.c | 6 +++++-
>>>  1 file changed, 5 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/ofproto/connmgr.c b/ofproto/connmgr.c
>>> index 9c5c633b4171..fa8f6cd0e83a 100644
>>> --- a/ofproto/connmgr.c
>>> +++ b/ofproto/connmgr.c
>>> @@ -2140,7 +2140,7 @@ ofmonitor_report(struct connmgr *mgr, struct rule *rule,
>>>                   const struct rule_actions *old_actions)
>>>      OVS_REQUIRES(ofproto_mutex)
>>>  {
>>> -    if (rule_is_hidden(rule)) {
>>> +    if (!mgr || rule_is_hidden(rule)) {
>>>          return;
>>>      }
>>>
>>> @@ -2244,6 +2244,10 @@ ofmonitor_flush(struct connmgr *mgr)
>>>  {
>>>      struct ofconn *ofconn;
>>>
>>> +    if (!mgr) {
>>> +        return;
>>> +    }
>>> +
>>>      LIST_FOR_EACH (ofconn, connmgr_node, &mgr->conns) {
>>>          struct rconn_packet_counter *counter = ofconn->monitor_counter;
>>>
>>> --
>>> 2.7.4
>>>
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> 
> 
>