selftests/mm: check stat() return value in khugepaged get_finfo()

get_finfo() calls stat() to get metadata about the target directory, but
never checks the return value.  On failure, stat() returns -1 and leaves
path_stat unmodified, so path_stat.st_mode may contain uninitialized stack
data.

The code then checks S_ISDIR(path_stat.st_mode) against this potentially
garbage value.  This can produce a misleading "Not a directory" error when
the real problem is a nonexistent or inaccessible path, or, in the worst
case, the check could pass by chance on garbage data and let the function
continue using an invalid path_stat for the rest of its logic.

Check the return value and fail with a clear error message if stat()
fails, matching the error-handling style already used for statfs() and
read_file() later in the same function.

Link: https://lore.kernel.org/20260819121426.49500-1-anshumantewari123@gmail.com
Signed-off-by: Anshuman <anshumantewari123@gmail.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: SJ Park <sj@kernel.org>
Reviewed-by: Sarthak Sharma <sarthak.sharma@arm.com>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/tools/testing/selftests/mm/khugepaged.c b/tools/testing/selftests/mm/khugepaged.c
index d3a5367..1d2d6bd 100644 (file)
--- a/tools/testing/selftests/mm/khugepaged.c
+++ b/tools/testing/selftests/mm/khugepaged.c
@@ -124,7 +124,8 @@ static void get_finfo(const char *dir)
        char *str, *end;
 
        finfo.dir = dir;
-       stat(finfo.dir, &path_stat);
+       if (stat(finfo.dir, &path_stat))
+               ksft_exit_fail_perror("stat()");
        if (!S_ISDIR(path_stat.st_mode))
                ksft_exit_fail_msg("%s: Not a directory (%s)\n", __func__, finfo.dir);
        if (snprintf(finfo.path, sizeof(finfo.path), "%s/" TEST_FILE,