possibly memory corruption

[mrexodia]

Yesterday I was debugging some programs and after restarting I saw that the status label stayed stuck on Initializing. At first it didn't seem to impact anything, but pretty soon after that other things started breaking as well.

My steps to reproduce (yesterday, today it all works fine obviously):

• Load some debuggee
• Hold step for some time
• Press restart

There are two things that could happen:

1. The label stays stuck on initializing
2. The label stays stuck on paused (much more rare)

The first case means that TaskThread.WakeUp doesn't wake up the thread (ReleaseSemaphore fails with an invalid handle error)

The second case means that WaitForSingleObject in TaskThread.Loop always instantly returns and keeps executing the relevant function (GuiSetDebugState) with whatever the last value was (paused).

I tried running under appverifier, but that just hung the process so nothing useful came out of that for me.

[mrexodia]

Some progress:

Duncan (mrexodia), [04.11.17 19:25]
MOTHERFUCK

Duncan (mrexodia), [04.11.17 19:25]
@Nukem9 you on?

Duncan (mrexodia), [04.11.17 19:26]
because this shit is crazy

Duncan (mrexodia), [04.11.17 19:26]
the TaskThread didn't get memory corrupted, but somehow CloseHandle is called

Duncan (mrexodia), [04.11.17 19:26]
at first I had a named semaphore with handle 0x624

Duncan (mrexodia), [04.11.17 19:26]
then reloading a bunch of times to trigger the bug

Duncan (mrexodia), [04.11.17 19:27]
https://i.imgur.com/7Z20nM3.png

Duncan (mrexodia), [04.11.17 19:27]
I just smell kernel bugs

[mrexodia]

Relevant blog post: https://x64dbg.com/blog/2017/11/04/the-big-handle-gamble.html