[
https://issues.apache.org/jira/browse/ZOOKEEPER-3286?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]
Mate Szalay-Beko updated ZOOKEEPER-3286:
----------------------------------------
Fix Version/s: (was: 3.5.10)
> xid wrap-around causes connection loss/segfault when hitting predefined XIDs
> ----------------------------------------------------------------------------
>
> Key: ZOOKEEPER-3286
> URL: https://issues.apache.org/jira/browse/ZOOKEEPER-3286
> Project: ZooKeeper
> Issue Type: Bug
> Components: c client
> Affects Versions: 3.5.4
> Environment: CentOS 7.2
> Reporter: Christian Czezatke
> Priority: Minor
> Labels: pull-request-available
> Attachments: c-client-xid.diff
>
> Time Spent: 2.5h
> Remaining Estimate: 0h
>
> *Description:*
> The get_xid functions in mt_adaptor.c/st_adaptor.c return a 32 bit signed
> integer that is initialized to the current unix epoch timestamp on startup.
> This counter will eventually wrap around, which is not a problem per se,
> since the client does not expect XID values to monotonically increase: It
> just verifies that replies to operations come back in order by checking the
> XID of a request received against the next XID expected.
> (zookeeper.c:zookeeper_process).
> However, after a wrap-around the XID values will eventually collide with the
> reserved XIDs ad defined in zk_adaptor.h:
> * The first collision will be with SET_WATCHES_XID (-8): The reply to the
> request that happens to get tagged with -8 will be misinterpreted as a reply
> to SET_WATCHES. This causes the client to see a connection timeout.
> * The next collision will be with AUTH_XID (-4): At that point the client
> will segfault, when mis-interpreting the reply:
> #0 0x0000000000407645 in auth_completion_func (zh=0x61d010, rc=0) at
> src/zookeeper.c:1823
> #1 zookeeper_process (zh=zh@entry=0x61d010, events=<optimized out>) at
> src/zookeeper.c:2896
> #2 0x000000000040c34c in do_io (v=0x61d010) at src/mt_adaptor.c:451
> #3 0x00007ffff7bc8dc5 in start_thread () from /lib64/libpthread.so.0
> #4 0x00007ffff75f573d in clone () from /lib64/libc.so.6
> I hit this with a busy C client that runs for a very long time (months).
> Also, when a client spins in a tight loop trying to submit more operations
> even for a short period of time after a connection loss the xid values will
> increment very fast.
>
> *Proposed patch:*
> To avoid introducing any additional locking, this can be solved by just
> masking out the MSB in the xid returned by get_xid. Effectively this prevents
> the returned XID from ever going negative.
> To avoid a race when the static xid variable hits -1 eventually after a wrap,
> around, I propose to not initialize xid with the result of time(0) on
> startup. This is not needed. This also means that the get_xid function in
> mt_adapter.c no longer needs to be flagged as constructor.
> Proposed patch is attached.
>
> I ran into this on zookeeper 3.5.4 but other versions are likely affected as
> well.
--
This message was sent by Atlassian Jira
(v8.20.7#820007)
