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https://issues.apache.org/jira/browse/ZOOKEEPER-2443?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Patrick Hunt reassigned ZOOKEEPER-2443:
---------------------------------------
Assignee: Chris Nauroth
[~cnauroth], [~fpj], [~rgs] can you take a look at this? According to Paul the
issue was introduced in ZOOKEEPER-1029.
> Invalid Memory Access (SEGFAULT) and undefined behaviour in c client
> --------------------------------------------------------------------
>
> Key: ZOOKEEPER-2443
> URL: https://issues.apache.org/jira/browse/ZOOKEEPER-2443
> Project: ZooKeeper
> Issue Type: Bug
> Components: c client
> Reporter: Paul Asmuth
> Assignee: Chris Nauroth
>
> Hey,
> I encountered some issues with the zookeepeer c client.
> The problem starts in the zookeeper_init_internal method. A lot of
> initialization work is performed here and if any of the initialization
> routines fails, the code jumps to the "abort" label to perform various
> cleanup tasks [1]. The conceptual issue is that a bunch of the cleanup code
> tries to take locks on the zk structure that are only intialized in
> adaptor_init in line 1181 (at the very end of the zookeeper_init_internal
> method) [2]. So if we fail before reaching adaptor_init this causes trouble.
> One specific instance of an invalid memory access that this causes is in
> free_completions [3]. Here, in line 1651 zoo_lock_auth will fail because it
> tries to grab an invalid mutex, after which the a_list struct is
> uninitialized (the linked list next pointer points to random memory) and
> subsequently the free routine segfaults.
> An easy way to trigger this bug-path is to pass an invalid hostname, or do
> anything else that causes the zookeeper_init_internal method to fail before
> adaptor_init.
> In my local checkout/codebase, I have added correct initialization for the
> a_list struct in the free_completions routine, which at least fixes the
> segfault for now. However this still leaves the issue that the cleanup code
> tries to grab a lot of invalid locks, which all fail. I think in order to fix
> this properly, one would need to do a larger refactoring of the code (add
> another adaptor_preinit routine to the adaptor interface maybe?) and I wasn't
> sure if that would be appreciated, so I didn't attach a patch for now. If
> someone wants me to try and clean this up, I would be happy to give it a try.
> PS: I think this bug was introduced in SVN #1719528, which - as it seems -
> tried to work around the uninitialized locks problem by adding an int return
> code to all the lock_xxx functions, allowing them to indicate a failure. The
> change introduce the invalid memory access since some (always required) init
> code is only run after the lock was obtained successfully.
> However, I think there is a much large issue with the change and I think it
> must be reverted. Trying to lock an uninitialized mutex is undefined
> behaviour on POSIX and may lead to deadlocks, etc.
> >> If mutex does not refer to an initialized mutex object, the behavior of
> >> pthread_mutex_lock(), pthread_mutex_trylock(), and pthread_mutex_unlock()
> >> is undefined.
> http://pubs.opengroup.org/onlinepubs/9699919799/functions/pthread_mutex_lock.html
> [1] https://github.com/apache/zookeeper/blob/trunk/src/c/src/zookeeper.c#L1078
> [2] https://github.com/apache/zookeeper/blob/trunk/src/c/src/zookeeper.c#L1181
> [3] https://github.com/apache/zookeeper/blob/trunk/src/c/src/zookeeper.c#L1651
> ------------------
> BACKTRACE
> Program received signal SIGSEGV, Segmentation fault.
> 0x000000010004f6d5 in free_auth_completion (a_list=0x7fff5fbff048) at
> /deps/3rdparty/zookeeper/source/src/zookeeper.c:260
> 260 tmp = tmp->next;
> #0 0x000000010004f6d5 in free_auth_completion (a_list=0x7fff5fbff048) at
> /deps/3rdparty/zookeeper/source/src/zookeeper.c:260
> #1 0x000000010004f500 in free_completions (zh=0x1003022f0, callCompletion=1,
> reason=-116) at /deps/3rdparty/zookeeper/source/src/zookeeper.c:1219
> #2 0x0000000100057bfd in cleanup_bufs (zh=0x1003022f0, callCompletion=1,
> rc=-116) at /deps/3rdparty/zookeeper/source/src/zookeeper.c:1227
> #3 0x000000010004ee42 in destroy (zh=0x1003022f0) at
> /deps/3rdparty/zookeeper/source/src/zookeeper.c:393
> #4 0x000000010004eaf3 in zookeeper_init (host=0x1006005b0
> "xxxinvalidhostname:2181", watcher=0x100007670 <xxx::zk_watch_cb(_zhandle*,
> int, int, char const*, void*)>,
> recv_timeout=10000, clientid=0x0, context=0x100600350, flags=0) at
> /deps/3rdparty/zookeeper/source/src/zookeeper.c:877
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