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

[David Laight <david.laight.linux@gmail.com>]

On Sun, 21 Dec 2025 20:26:37 +0800
Li Wang <liwang@redhat.com> 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.

And sscanf() will just ignore invalid trailing characters.
Probably much the same as atoi() apart from a leading '-'.

Maybe you could use "%zu%c" and check the count is 1 - but I bet
some static checker won't like that.

Using strtoul() and checking the terminating character is 'reasonable',
but won't detect overflow.

	David

> 
> --- 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");