6.18-stable review patch. If anyone has any objections, please let me know.
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From: Wake Liu wakel@google.com
commit 632b874d59a36caf829ab5790dafb90f9b350fd6 upstream.
In the thread_state_get() function, the logic to find the thread's state character was using `sizeof(header) - 1` to calculate the offset from the "State:\t" string.
The `header` variable is a `const char *` pointer. `sizeof()` on a pointer returns the size of the pointer itself, not the length of the string literal it points to. This makes the code's behavior dependent on the architecture's pointer size.
This bug was identified on a 32-bit ARM build (`gsi_tv_arm`) for Android, running on an ARMv8-based device, compiled with Clang 19.0.1.
On this 32-bit architecture, `sizeof(char *)` is 4. The expression `sizeof(header) - 1` resulted in an incorrect offset of 3, causing the test to read the wrong character from `/proc/[tid]/status` and fail.
On 64-bit architectures, `sizeof(char *)` is 8, so the expression coincidentally evaluates to 7, which matches the length of "State:\t". This is why the bug likely remained hidden on 64-bit builds.
To fix this and make the code portable and correct across all architectures, this patch replaces `sizeof(header) - 1` with `strlen(header)`. The `strlen()` function correctly calculates the string's length, ensuring the correct offset is always used.
Link: https://lkml.kernel.org/r/20251210091408.3781445-1-wakel@google.com Fixes: f60b6634cd88 ("mm/selftests: add a test to verify mmap_changing race with -EAGAIN") Signed-off-by: Wake Liu wakel@google.com Acked-by: Peter Xu peterx@redhat.com Reviewed-by: Mike Rapoport (Microsoft) rppt@kernel.org Cc: Bill Wendling morbo@google.com Cc: Justin Stitt justinstitt@google.com Cc: Liam Howlett liam.howlett@oracle.com Cc: Lorenzo Stoakes lorenzo.stoakes@oracle.com Cc: Michal Hocko mhocko@suse.com Cc: Nathan Chancellor nathan@kernel.org Cc: Shuah Khan shuah@kernel.org Cc: Suren Baghdasaryan surenb@google.com Cc: Vlastimil Babka vbabka@suse.cz Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- tools/testing/selftests/mm/uffd-unit-tests.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/tools/testing/selftests/mm/uffd-unit-tests.c +++ b/tools/testing/selftests/mm/uffd-unit-tests.c @@ -1317,7 +1317,7 @@ static thread_state thread_state_get(pid p = strstr(tmp, header); if (p) { /* For example, "State:\tD (disk sleep)" */ - c = *(p + sizeof(header) - 1); + c = *(p + strlen(header)); return c == 'D' ? THR_STATE_UNINTERRUPTIBLE : THR_STATE_UNKNOWN; }