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Fix: use-after-free after ClientNetworkCoordinatorSocketHandler::CloseAllConnections() #9534

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merged 1 commit into from Sep 5, 2021

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TrueBrain
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Motivation / Problem

While debugging a GC issue, I managed to cause a use-after-free. Example flow:

Start your own server, and while your server is being probed (takes ~3 seconds), kill the connection (for example by modifying the code or running your own GC that does this).

Possibly there are other ways to trigger a CloseAllConnections.

Description

The function clears all stun-handlers. This causes all of those
objects to be destroyed.
A handler can have a pending connecter, which was only killed in
case CloseConnection() was called. This is never the case when
the object is destroyed. In result, the connecter could finish
and cause a use-after-free by calling into the (now deleted)
handler.

I have no clue why I initially wrote it in CloseConnection() with this comment, and that worries me a bit. I remember there was something special about these objects, but .. yeah, can't remember, and this seems to be the proper solution.

Limitations

Checklist for review

Some things are not automated, and forgotten often. This list is a reminder for the reviewers.

  • The bug fix is important enough to be backported? (label: 'backport requested')
  • This PR touches english.txt or translations? Check the guidelines
  • This PR affects the save game format? (label 'savegame upgrade')
  • This PR affects the GS/AI API? (label 'needs review: Script API')
    • ai_changelog.hpp, gs_changelog.hpp need updating.
    • The compatibility wrappers (compat_*.nut) need updating.
  • This PR affects the NewGRF API? (label 'needs review: NewGRF')

…eAllConnections()

The function clears all stun-handlers. This causes all of those
objects to be destroyed.
A handler can have a pending connecter, which was only killed in
case CloseConnection() was called. This is never the case when
the object is destroyed. In result, the connecter could finish
and cause a use-after-free by calling into the (now deleted)
handler.
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@LordAro LordAro left a comment

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Sure.

@TrueBrain TrueBrain merged commit f656b0a into OpenTTD:master Sep 5, 2021
@TrueBrain TrueBrain deleted the fix-closing-connecter branch September 5, 2021 16:17
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2 participants