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FIX #7693: concurrent task execution: fixed dereference of NULL #7694

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In the function TaskConcurrentCancelCheck() the pointer "task" was utilized after checking against NULL, which can lead to dereference of the null pointer.
To avoid the problem, added a separate handling of the case when the pointer is null with an interruption of execution.

Fixes: 1f8675d("nonblocking concurrent task execution via background workers")

@ProjectMutilation ProjectMutilation changed the title FIX#7693: concurrent task execution: fixed dereference of NULL FIX #7693: concurrent task execution: fixed dereference of NULL Sep 30, 2024
if (!task)
{
ereport(ERROR, (errmsg("task is invalid")));
}
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You message is not very helpful.

See around line 300 a similar pattern, here patched:

		if (!task)
		{
			ereport(ERROR, (errmsg("no task found with taskid: %ld", handleEntry->taskid)));
		}

Also I suggest to move your patch one line up (before the assignment).

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I wonder if the error message should not be more strong: 'unexpected missing task id: ...;'

Maybe an Assert() given "task" is always expected to be set....

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ereport(ERROR, ...) doesn't return control

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I'm unsure what Citus guidelines are here but I don't think task is ever supposed to be NULL in this function.
That's why maybe an Assert() and not an ereport(ERROR)...

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I'm not sure whether the use of the "assert" is more appropriate, but the ereport(ERROR) is a normal shutdown in the event of errors.


if (!task || task->status == BACKGROUND_TASK_STATUS_CANCELLING)
if (task->status == BACKGROUND_TASK_STATUS_CANCELLING)
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that's a bit of a trouble, in the "else" part too it depends on task being set.

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@ProjectMutilation ProjectMutilation Oct 8, 2024

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if exit the function earlier, it will not be trouble

In the function TaskConcurrentCancelCheck() the pointer "task"
was utilized after checking against NULL, which can lead
to dereference of the null pointer.
To avoid the problem, added a separate handling of the case
when the pointer is null with an interruption of execution.

Fixes: 1f8675d("nonblocking concurrent task execution via background workers")

Signed-off-by: Maksim Korotkov <[email protected]>
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2 participants