Fixed Thread reply count is incorrect after soft-deleting large number of posts in a long enough thread

[Xon]

Affected version

2.3.10

If a user deletes a large number of individual posts in a sufficiently long thread, there is a race for xf_thread.reply_count being set to the actual correct value. This can result in the thread being "broken" where position numbers are re-used.

This is because Thread::postRemoved() acts on the existing loaded Thread object when adjusting reply_count, and not the actual database record.

Ideally the xf_thread record needs to be locked at the start of the update and the actual database value pushed into the thread entity and then adjusted. Switching to SQL for atomically incrementing/decrementing reply_count is another solution, and then updating the in-memory entity similar to how alert counts are handled.

This race condition probably applies to a post being hard-deleted as well.

 

[XF Bug Bot]

Thank you for reporting this issue, it has now been resolved. We are aiming to include any changes that have been made in a future XF release (2.3.14).

Change log:

Prevent wrong reply counts and reused post numbers when posts are deleted during new replies

There may be a delay before changes are rolled out to the XenForo Community.