[v3] selftests/mm: hugetlb cgroup charging: robustness fixes

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

Posted by Li Wang 1 month, 2 weeks ago

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");
-- 
2.49.0

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

Posted by Waiman Long 1 month, 2 weeks ago

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>

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

Posted by David Laight 1 month, 2 weeks ago

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");