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

[Li Wang <liwang@redhat.com>]

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