linux-kernel - Re: [PATCH 1/3] selftests/mm/write_to_hugetlbfs: parse -s with strtoull and use size

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Message-Id: <20251220105811.3516167661cd696f464cc3b0@linux-foundation.org>
Date: Sat, 20 Dec 2025 10:58:11 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: Li Wang <liwang@...hat.com>
Cc: linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-mm@...ck.org, David Hildenbrand <david@...nel.org>, Mark Brown
 <broonie@...nel.org>, Shuah Khan <shuah@...nel.org>, Waiman Long
 <longman@...hat.com>
Subject: Re: [PATCH 1/3] selftests/mm/write_to_hugetlbfs: parse -s with
 strtoull and use size_t

On Sat, 20 Dec 2025 19:16:43 +0800 Li Wang <liwang@...hat.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.
> 
> --- 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

Can we fix that typo while we're in there?  "reservation".

>  ...
>  # Writing to this path: /mnt/huge/test
>  # Writing this size: -1610612736        <--------
> 
> Switch size to size_t and parse -s using strtoull() with proper validation.
> Also print the size using %zu.
> 
> This makes the test utility more robust and avoids undefined/incorrect
> behavior with large or invalid -s values.
> 
> ...
>
> --- 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 +86,20 @@ int main(int argc, char **argv)
>  	while ((c = getopt(argc, argv, "s:p:m:owlrn")) != -1) {
>  		switch (c) {
>  		case 's':
> -			size = atoi(optarg);
> +			errno = 0;
> +			char *end = NULL;
> +			unsigned long long tmp = strtoull(optarg, &end, 10);

Coding-style nits: we do accept c99-style definitions nowadays but I do
think our eyes prefer the less surprising "definitions come before
code" style.  So the above could be

			char *end = NULL;
			unsigned long long tmp = strtoull(optarg, &end, 10);

			errno = 0;

Also, `errno' belongs to libc.  It seems wrong to be altering it from
within our client code.

> +			if (errno || end == optarg || *end != '\0') {
> +				errno = EINVAL;
> +				perror("Invalid -s size");
> +				exit_usage();
> +			}
> +			if (tmp == 0) {
> +				errno = EINVAL;
> +				perror("size not found");
> +				exit_usage();
> +			}
> +			size = (size_t)tmp;
>  			break;

I'm not really clear on what problems we're trying to solve here, but
this all seems like a lot of fuss.  Can we just do

	if (sscanf(optarg, "%zu", &size) != 1)

?

>  		case 'p':
>  			strncpy(path, optarg, sizeof(path) - 1);
> @@ -131,7 +144,7 @@ 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");