Re: [PATCH v3 1/3] selftests/mm/write_to_hugetlbfs: parse -s as size_t

Waiman Long
2025-12-21T20:23:33Z

On 12/21/25 7:26 AM, Li Wang wrote:
> write_to_hugetlbfs currently parses the -s size argument with atoi()
> into an int. This silently accepts malformed input, cannot report overflow,
> and can truncate large sizes.
>
> --- Error log ---
> # uname -r
> 6.12.0-xxx.el10.aarch64+64k
>
> # ls /sys/kernel/mm/hugepages/hugepages-*
> hugepages-16777216kB/ hugepages-2048kB/ hugepages-524288kB/
>
> #./charge_reserved_hugetlb.sh -cgroup-v2
> # -----------------------------------------
> ...
> # nr hugepages = 10
> # writing cgroup limit: 5368709120
> # writing reseravation limit: 5368709120
> ...
> # Writing to this path: /mnt/huge/test
> # Writing this size: -1610612736 <--------
>
> Switch the size variable to size_t and parse -s with sscanf("%zu", ...).
> Also print the size using %zu.
>
> This avoids incorrect behavior with large -s values and makes the utility
> more robust.
>
> Signed-off-by: Li Wang <liwang@redhat.com>
> Cc: David Hildenbrand <david@kernel.org>
> Cc: Mark Brown <broonie@kernel.org>
> Cc: Shuah Khan <shuah@kernel.org>
> Cc: Waiman Long <longman@redhat.com>
> Acked-by: David Hildenbrand (Red Hat) <david@kernel.org>
> ---
> tools/testing/selftests/mm/write_to_hugetlbfs.c | 9 ++++++---
> 1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/tools/testing/selftests/mm/write_to_hugetlbfs.c b/tools/testing/selftests/mm/write_to_hugetlbfs.c
> index 34c91f7e6128..ecb5f7619960 100644
> --- a/tools/testing/selftests/mm/write_to_hugetlbfs.c
> +++ b/tools/testing/selftests/mm/write_to_hugetlbfs.c
> @@ -68,7 +68,7 @@ int main(int argc, char **argv)
> int key = 0;
> int *ptr = NULL;
> int c = 0;
> - int size = 0;
> + size_t size = 0;
> char path[256] = "";
> enum method method = MAX_METHOD;
> int want_sleep = 0, private = 0;
> @@ -86,7 +86,10 @@ int main(int argc, char **argv)
> while ((c = getopt(argc, argv, "s:p:m:owlrn")) != -1) {
> switch (c) {
> case 's':
> - size = atoi(optarg);
> + if (sscanf(optarg, "%zu", &size) != 1) {
> + perror("Invalid -s.");
> + exit_usage();
> + }
> break;
> case 'p':
> strncpy(path, optarg, sizeof(path) - 1);
> @@ -131,7 +134,7 @@ int main(int argc, char **argv)
> }
>
> if (size != 0) {
> - printf("Writing this size: %d\n", size);
> + printf("Writing this size: %zu\n", size);
> } else {
> errno = EINVAL;
> perror("size not found");

LGTM

Acked-by: Waiman Long <longman@redhat.com>