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Fix deadlock with Windows Loader during execute_while_frozen #51

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Fix deadlock with Windows Loader during execute_while_frozen #51

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3d5b242
Fix deadlock with Windows Loader during execute_while_frozen
praydog Dec 28, 2023
37d2810
Also unlock the loader for the visit_fn
praydog Dec 28, 2023
ebc0d28
NULL->nullptr
praydog Dec 28, 2023
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30 changes: 30 additions & 0 deletions src/thread_freezer.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -25,6 +25,20 @@ void execute_while_frozen(
int num_threads_frozen;
auto first_run = true;

ULONG_PTR loader_magic = 0;

typedef NTSTATUS (WINAPI* PFN_LdrLockLoaderLock)(ULONG Flags, ULONG *State, ULONG_PTR *Cookie);
typedef NTSTATUS (WINAPI* PFN_LdrUnlockLoaderLock)(ULONG Flags, ULONG_PTR Cookie);

const auto ntdll = GetModuleHandleW(L"ntdll.dll");

auto lock_loader = (PFN_LdrLockLoaderLock)GetProcAddress(ntdll, "LdrLockLoaderLock");
auto unlock_loader = (PFN_LdrUnlockLoaderLock)GetProcAddress(ntdll, "LdrUnlockLoaderLock");

if (lock_loader != nullptr && unlock_loader != nullptr) {
Comment on lines +30 to +38
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I would prefer if these were just imported normally. See

safetyhook/src/thread_freezer.cpp

Lines 14 to 19 in 521ae9f

extern "C" {
NTSTATUS
NTAPI
NtGetNextThread(HANDLE ProcessHandle, HANDLE ThreadHandle, ACCESS_MASK DesiredAccess, ULONG HandleAttributes,
ULONG Flags, PHANDLE NewThreadHandle);
}

lock_loader(0, nullptr, &loader_magic);
}

do {
num_threads_frozen = 0;
HANDLE thread{};
Expand Down Expand Up @@ -73,7 +87,18 @@ void execute_while_frozen(
}

if (visit_fn) {
// Unlock the loader lock.
if (lock_loader != nullptr && unlock_loader != nullptr) {
unlock_loader(0, loader_magic);
}

visit_fn(thread_id, thread, thread_ctx);

// Lock it again.
if (lock_loader != nullptr && unlock_loader != nullptr) {
loader_magic = 0;
lock_loader(0, nullptr, &loader_magic);
}
}

++num_threads_frozen;
Expand All @@ -82,6 +107,11 @@ void execute_while_frozen(
first_run = false;
} while (num_threads_frozen != 0);

// Unlock the loader lock.
if (lock_loader != nullptr && unlock_loader != nullptr) {
unlock_loader(0, loader_magic);
}

// Run the function.
if (run_fn) {
run_fn();
Expand Down