Re: [PATCH] selftests/mm: fix unchecked ftruncate return value in soft-dirty test

[Sarthak Sharma <sarthak.sharma@arm.com>]

On 8/18/26 7:02 PM, Anshuman wrote:
> 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.
> 
> Signed-off-by: Anshuman <anshumantewari123@gmail.com>
> ---

Looks good to me.

Reviewed-by: Sarthak Sharma <sarthak.sharma@arm.com>

>  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 fb1864a68..a52ef79dd 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)