ntdll/tests: Fix incorrect calculation of context length in test_copy_context().

`(BYTE *)dst_ex - (BYTE *)dst` is the size of the legacy context, but `dst_ex->All` already contains the legacy context. Therefore, `context_length` has the legacy context size added *twice*. This becomes a problem when `context_length` exceeds `sizeof(src_context_buffer)`. This confuses `check_changes_in_range()`, causing out-of-bounds read and unpredictable test results.

ntdll/tests: Fix incorrect calculation of context length in test_copy_context().
7ba9dea9 · Jinoh Kang · Alexandre Julliard · 3995ff24 · 7ba9dea9
Commit 7ba9dea9 authored Jan 06, 2024 by Jinoh Kang Committed by Alexandre Julliard Jan 08, 2024
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exception.c dlls/ntdll/tests/exception.c +1 -1

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--- a/dlls/ntdll/tests/exception.c
+++ b/dlls/ntdll/tests/exception.c
@@ -11952,7 +11952,7 @@ static void test_copy_context(void)
        *(DWORD *)((BYTE *)dst + flags_offset) = 0;
        *(DWORD *)((BYTE *)src + flags_offset) = 0;
-        context_length = (BYTE *)dst_ex - (BYTE *)dst + dst_ex->All.Length;
+        context_length = dst_ex->All.Length;
        if (flags & 0x40)
        {