From c7a4e939f87cc75a9a664485b10c0bf7db632156 Mon Sep 17 00:00:00 2001 From: Anshuman Date: Tue, 18 Aug 2026 19:02:06 +0530 Subject: [PATCH] selftests/mm: fix unchecked ftruncate return value in soft-dirty test test_mprotect() calls ftruncate() to resize the backing file before mmap()'ing it, but never checks the return value. If ftruncate() fails, the file may remain shorter than the requested mapping size. The subsequent mmap() with MAP_SHARED can still succeed in this case, but the very next line writes directly into the mapped memory (*map = 1), which can trigger SIGBUS if the mapping extends beyond the actual file size. Check the return value and fail cleanly with ksft_exit_fail_msg() if ftruncate() fails, matching the error-handling style already used for the mmap() call immediately below it. Link: https://lore.kernel.org/20260818133206.39503-1-anshumantewari123@gmail.com Signed-off-by: Anshuman Reviewed-by: Andrew Morton Reviewed-by: Sarthak Sharma Cc: David Hildenbrand Cc: Shuah Khan Signed-off-by: Andrew Morton --- tools/testing/selftests/mm/soft-dirty.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/tools/testing/selftests/mm/soft-dirty.c b/tools/testing/selftests/mm/soft-dirty.c index e198facf78bb..5f278913c4d7 100644 --- a/tools/testing/selftests/mm/soft-dirty.c +++ b/tools/testing/selftests/mm/soft-dirty.c @@ -152,7 +152,8 @@ static void test_mprotect(int pagemap_fd, int pagesize, bool anon) return; } unlink(fname); - ftruncate(test_fd, pagesize); + if (ftruncate(test_fd, pagesize) != 0) + ksft_exit_fail_msg("ftruncate failed\n"); map = mmap(NULL, pagesize, PROT_READ|PROT_WRITE, MAP_SHARED, test_fd, 0); if (map == MAP_FAILED)