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

[Yi-Hung Wei]

On Tue, Feb 16, 2021 at 1:06 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>
> ---

LGTM.

Acked-by: Yi-Hung Wei <yihung.wei at gmail.com>