Re: [PATCH 1/2] selftests/bpf: Fix read_iter buffer termination in test_bpffs

[Yonghong Song <yonghong.song@linux.dev>]

On 3/10/26 3:21 AM, Sun Jian wrote:
> read_iter() always NUL-terminated at the end of the buffer, so strstr()
> could scan uninitialized stack bytes on short reads. Terminate at len and
> use O_RDONLY.
>
> Signed-off-by: Sun Jian <sun.jian.kdev@gmail.com>
> ---
>   tools/testing/selftests/bpf/prog_tests/test_bpffs.c | 6 +++---
>   1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/test_bpffs.c b/tools/testing/selftests/bpf/prog_tests/test_bpffs.c
> index ea933fd151c3..e8021ff0581c 100644
> --- a/tools/testing/selftests/bpf/prog_tests/test_bpffs.c
> +++ b/tools/testing/selftests/bpf/prog_tests/test_bpffs.c
> @@ -17,11 +17,11 @@ static int read_iter(char *file)
>   	char buf[1024];
>   	int fd, len;
>   
> -	fd = open(file, 0);
> +	fd = open(file, O_RDONLY);
>   	if (fd < 0)
>   		return -1;
> -	while ((len = read(fd, buf, sizeof(buf))) > 0) {
> -		buf[sizeof(buf) - 1] = '\0';
> +	while ((len = read(fd, buf, sizeof(buf) - 1)) > 0) {
> +		buf[len] = '\0';
>   		if (strstr(buf, "iter")) {
>   			close(fd);
>   			return 0;

The change here is unnecessary. Typically /sys/fs/bpf/ should be mounted
earlier and the 'iter' should appear with early prog/map id's. This ensure
'iter' will be discovered earlier. If you have an issue for this, fix
your setup.

>
> base-commit: 1f318b96cc84d7c2ab792fcc0bfd42a7ca890681