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From "Enrico Olivelli (Jira)" <j...@apache.org>
Subject [jira] [Updated] (ZOOKEEPER-1519) Zookeeper Async calls can reference free()'d memory
Date Fri, 06 Sep 2019 15:45:06 GMT

     [ https://issues.apache.org/jira/browse/ZOOKEEPER-1519?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Enrico Olivelli updated ZOOKEEPER-1519:
---------------------------------------
    Fix Version/s:     (was: 3.5.6)

> Zookeeper Async calls can reference free()'d memory
> ---------------------------------------------------
>
>                 Key: ZOOKEEPER-1519
>                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-1519
>             Project: ZooKeeper
>          Issue Type: Bug
>          Components: c client
>    Affects Versions: 3.3.3, 3.3.6
>         Environment: Ubuntu 11.10, Ubuntu packaged Zookeeper 3.3.3 with some backported
fixes.
>            Reporter: Mark Gius
>            Assignee: Daniel Lescohier
>            Priority: Major
>             Fix For: 3.6.0, 3.5.7
>
>         Attachments: zookeeper-1519.patch
>
>
> zoo_acreate() and zoo_aset() take a char * argument for data and prepare a call to zookeeper.
 This char * doesn't seem to be duplicated at any point, making it possible that the caller
of the asynchronous function might potentially free() the char * argument before the zookeeper
library completes its request.  This is unlikely to present a real problem unless the freed
memory is re-used before zookeeper consumes it.  I've been unable to reproduce this issue
using pure C as a result.
> However, ZKPython is a whole different story.  Consider this snippet:
>   ok = zookeeper.acreate(handle, path, json.dumps(value), 
>                          acl, flags, callback)
>   assert ok == zookeeper.OK
> In this snippet, json.dumps() allocates a string which is passed into the acreate().
 When acreate() returns, the zookeeper request has been constructed with a pointer to the
string allocated by json.dumps().  Also when acreate() returns, that string is now referenced
by 0 things (ZKPython doesn't bump the refcount) and the string is eligible for garbage collection
and re-use.  The Zookeeper request now has a pointer to dangerous freed memory.
> I've been seeing odd behavior in our development environments for some time now, where
it appeared as though two separate JSON payloads had been joined together.  Python has been
allocating a new JSON string in the middle of the old string that an incomplete zookeeper
async call had not yet processed.
> I am not sure if this is a behavior that should be documented, or if the C binding implementation
needs to be updated to create copies of the data payload provided for aset and acreate.



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