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https://issues.apache.org/jira/browse/IMPALA-11365?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17557175#comment-17557175
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ASF subversion and git services commented on IMPALA-11365:
----------------------------------------------------------

Commit da14fdcf35da28d2ff86c6ca9413a95cc3f8f346 in impala's branch 
refs/heads/master from Daniel Becker
[ https://gitbox.apache.org/repos/asf?p=impala.git;h=da14fdcf3 ]

IMPALA-11365: Dereferencing null pointer in TopNNode

In the constructor of TopNNode, if 'pnode.partition_comparator_config_'
is NULL, we initialise 'partition_cmp_' with a NULL pointer. However,
when initialising 'partition_heaps_', we dereference 'partition_cmp_'
because 'ComparatorWrapper' expects a reference.

This has so far not lead to a crash because in this case the comparator
of 'partition_heaps_' is not used, but assigning a NULL pointer to a
reference is undefined behaviour.

After this change, instead of assigning a NULL pointer to
'partition_cmp_', we use a dummy comparator, and no undefined behaviour
is invoked.

Change-Id: I0b15b06f608b4d17fdf8a24e05967aaa16ebb79c
Reviewed-on: http://gerrit.cloudera.org:8080/18629
Reviewed-by: Zoltan Borok-Nagy <[email protected]>
Tested-by: Impala Public Jenkins <[email protected]>


> Dereferencing null pointer in TopNNode
> --------------------------------------
>
>                 Key: IMPALA-11365
>                 URL: https://issues.apache.org/jira/browse/IMPALA-11365
>             Project: IMPALA
>          Issue Type: Bug
>            Reporter: Daniel Becker
>            Assignee: Daniel Becker
>            Priority: Major
>
> In the constructor of TopNNode, if {{pnode.partition_comparator_config_}} is 
> NULL, we initialise {{partition_cmp_}} with a NULL pointer. However, when 
> initialising {{{}partition_heaps_{}}}, we dereference {{partition_cmp_}} 
> because {{ComparatorWrapper}} expects a reference.
> This has so far not lead to a crash because in this case the comparator of 
> {{partition_heaps_}} is not used, but assigning a NULL pointer to a reference 
> is undefined behaviour.



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