NtClose hook improvements: #31
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- Change the fast mutex guarding the NtClose hook to a kernel mutex. This is slower but safer since it prevents a deadlock in the case that NtClose recursively calls itself, which is highly unlikely but possible - Use ObQueryObjectAuditingByHandle() to test handle validity. This has the advantage of not needing to clear and reset the process debug port each time ObCloseHandle is called. This way other kernel threads will never see a NULL debug port on a process that is actually being debugged - Remove the DebugPort class, which was mostly a lot of hairy version specific code to find the debug port offset. This is no longer needed due to above change Also add a bunch of casts (HANDLE to ULONG) to satisfy the VS2017 compiler
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- Change the fast mutex guarding the NtClose hook to a kernel mutex. This is slower but safer since it prevents a deadlock in the case that NtClose recursively calls itself, which is highly unlikely but possible - Use ObQueryObjectAuditingByHandle() to test handle validity. This has the advantage of not needing to clear and reset the process debug port each time ObCloseHandle is called. This way other kernel threads will never see a NULL debug port on a process that is actually being debugged - Remove the DebugPort class, which was mostly a lot of hairy version specific code to find the debug port offset. This is no longer needed due to above change Also add a bunch of casts (HANDLE to ULONG) to satisfy the VS2017 compiler
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See #29. (2)
I'm not completely clear on the amount of performance degradation caused by going from a fast mutex to a regular kernel mutex. If this turns out to be an issue, shared pushlocks could be an alternative (this would allow multiple simultaneous readers, but exclusive acquire attempts while there are shared owners will guarantee a deadlock.) Pushlocks are also undocumented of course, but when has that ever stopped anyone?