[Bug 50194] New: x64dbg snapshots >= 2020-11-12_05-12 crashes on unimplemented function ntdll.dll.NtCreateDebugObject when attaching to process

[WineHQ Bugzilla]

https://bugs.winehq.org/show_bug.cgi?id=50194

            Bug ID: 50194
           Summary: x64dbg snapshots >= 2020-11-12_05-12 crashes on
                    unimplemented function ntdll.dll.NtCreateDebugObject
                    when attaching to process
           Product: Wine
           Version: 5.22
          Hardware: x86-64
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P2
         Component: ntdll
          Assignee: wine-bugs at winehq.org
          Reporter: focht at gmx.net
      Distribution: ---

Hello folks,

as it says. I've reported it to x64dbg project as well since they switched the
debug engine implementation to use native API for attaching to processes.

https://github.com/x64dbg/x64dbg/issues/2525

Copy/pasta from there:

...

Symptom: attaching to any 32-bit or 64-bit process results in x32dbg/x64dbg
crash. If x32dbg/x64dbg is registered as default crash handler you get a nice
debugger crash "fork" bomb ;-)

It crashes on unimplemented NtCreateDebugObject() which is native API.

https://source.winehq.org/git/wine.git/blob/40d4fbe45997a1820296e7909ba2212518bcfacc:/dlls/ntdll/ntdll.spec#l162

--- snip ---
 162 # @ stub NtCreateDebugObject
--- snip ---

Even with a small stub it wouldn't work because NtDebugActiveProcess is a stub
as well.

https://source.winehq.org/git/wine.git/blob/40d4fbe45997a1820296e7909ba2212518bcfacc:/dlls/ntdll/ntdll.spec#l193

The native API used to implement remote breakin:

https://github.com/x64dbg/TitanEngine/blob/91f57815c886d6bef94f1b512d60c5e2d8bb43fe/TitanEngine/Global.Debugger.cpp#L246

--- snip ---
static NTSTATUS NTAPI DbgUiConnectToDbg_()
{
    if(NtCurrentTeb()->DbgSsReserved[1] != NULL)
        return STATUS_SUCCESS;

    OBJECT_ATTRIBUTES ObjectAttributes;
    InitializeObjectAttributes(&ObjectAttributes, NULL, 0, NULL, NULL);
    return NtCreateDebugObject(&NtCurrentTeb()->DbgSsReserved[1],
DEBUG_ALL_ACCESS, &ObjectAttributes, 0);
}

// Source:
https://github.com/mirror/reactos/blob/c6d2b35ffc91e09f50dfb214ea58237509329d6b/reactos/dll/win32/kernel32/client/debugger.c#L480
BOOL WINAPI DebugActiveProcess_(IN DWORD dwProcessId)
{
    /* Connect to the debugger */
    NTSTATUS Status = DbgUiConnectToDbg_();
    if(!NT_SUCCESS(Status))
    {
        BaseSetLastNTError(Status);
        return FALSE;
    }

    /* Get the process handle */
    HANDLE Handle = ProcessIdToHandle(dwProcessId);
    if(!Handle)
    {
        return FALSE;
    }

    /* Now debug the process */
    Status = DbgUiDebugActiveProcess_(Handle);

    /* Close the handle since we're done */
    NtClose(Handle);

    /* Check if debugging worked */
    if(!NT_SUCCESS(Status))
    {
        /* Fail */
        BaseSetLastNTError(Status);
        return FALSE;
    }

    /* Success */
    return TRUE;
}
--- snip ---

Apparently this debugging functionality which makes use of native API was
switched to being a debug engine default here:

https://github.com/x64dbg/TitanEngine/commit/0a1c3236b84ab1e6022116e38df1cc586280383e
("Make SafeAttach the default")

Previously it could be controlled by *SafeAttach* config setting which is still
there but now no longer usable:

https://github.com/x64dbg/x64dbg/blob/dad16543c320640fe681b8d897235bf8d6c301ae/src/dbg/_exports.cpp#L1018

--- snip ---
        SetEngineVariable(UE_ENGINE_SAFE_ATTACH, settingboolget("Engine",
"SafeAttach"));
--- snip ---

A workaround exists: use the last snapshot before the breaking change:

https://sourceforge.net/projects/x64dbg/files/snapshots/snapshot_2020-11-05_15-25.zip/download

As already mentioned a simple stub prevents the crash but doesn't make
debugging work.

--- snip ---
$ wine ./x32dbg.exe 
...
0144:fixme:process:NtCreateDebugObject (0x7ff72f24 1f000f 0x614fe78 0), stub!
0144:fixme:process:NtDebugActiveProcess (0x214 (nil)), stub!
--- snip ---

I will create follow-up bug(s) to cover the missing functionality.

$ sha1sum snapshot_2020-11-12_05-12.zip 
6e88d4ce8fb967d08b381084f9ab805e5bcc4f18  snapshot_2020-11-12_05-12.zip

$ du -sh snapshot_2020-11-12_05-12.zip 
32M    snapshot_2020-11-12_05-12.zip

$ wine --version
wine-5.22-96-g4957599bbf5

Regards

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