[jira] [Commented] (ZOOKEEPER-1906) zkpython: invalid data in GetData for empty node

["Michi Mutsuzaki (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/ZOOKEEPER-1906?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13955773#comment-13955773 ] 

Michi Mutsuzaki commented on ZOOKEEPER-1906:
--------------------------------------------

Hi Nikita,

Would you like to submit a patch with a testcase?

Thanks!
--Michi

> zkpython: invalid data in GetData for empty node
> ------------------------------------------------
>
>                 Key: ZOOKEEPER-1906
>                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-1906
>             Project: ZooKeeper
>          Issue Type: Bug
>          Components: contrib-bindings
>         Environment: FreeBSD
>            Reporter: Nikita Vetoshkin
>             Fix For: 3.5.0
>
>
> In python if we ask {{zookeeper.get}} (which translates into {{pyzoo_get}}) for empty node we can get trash in result on Python level. Issue is pretty tricky. It goes like this:
>   * python C extension allocates buffer with malloc {{buffer = malloc(sizeof(char)*buffer_len);}} and calls {{zoo_wget}} providing both {{buffer}} and {{buffer_len}}.
>   * deserialize_GetDataResponse deserializes empty buffer and sets {{buffer_len}} to -1 and {{zoo_wget}} returns.
>   * python C extension calls {{Py_BuildValue( "(s#,N)", buffer,buffer_len ...}} with {{buffer_len}} set to -1.
>   * {{Py_BuildValue}} calls {{do_mkvalue}} to build python string which falls back to {{strlen(str)}} in case string length ({{buffer_len < 0}}) - that's our case.
>   * *usually* strlen returns 0, because e.g. linux uses magic zero filled page as result of mmap (which is being copied upon page fault, i.e. when you want to write to it)
>   * everything works!
> But on FreeBSD (not always) we can get random data in {{malloc}} result and this trash will be exposed to the user.
> Not sure about the right way to fix this, but something like
> {noformat}
> Index: src/contrib/zkpython/src/c/zookeeper.c
> ===================================================================
> --- src/contrib/zkpython/src/c/zookeeper.c	(revision 1583238)
> +++ src/contrib/zkpython/src/c/zookeeper.c	(working copy)
> @@ -1223,7 +1223,7 @@
>    }
>  
>    PyObject *stat_dict = build_stat( &stat );
> -  PyObject *ret = Py_BuildValue( "(s#,N)", buffer,buffer_len, stat_dict );
> +  PyObject *ret = Py_BuildValue( "(s#,N)", buffer,buffer_len < 0 ? 0 : buffer_len, stat_dict );
>    free(buffer);
>  
>    return ret;
> {noformat}
> should do the trick



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