On Mon, 22 Dec 2025 09:45:41 +0800 Li Wang liwang@redhat.com wrote:
On Mon, Dec 22, 2025 at 6:11 AM David Laight david.laight.linux@gmail.com wrote:
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.
Yes, that would be stronger, since it would reject trailing garbage. But for a selftest this is probably sufficient: switching to size_t and parsing with "%zu" already avoids the int truncation issue.
Have you checked at what does sscanf() does with an overlong digit string? I'd guess that it just processes all the digits and then masks the result to fix (like the kernel one does).
It reality scanf() is 'not the function you are lookign for'.
IIRC the 'SUS' (used to) say that this was absolutely fine for command line parsing for 'standard utilities'.
It is best to use strtoul() and check the 'end' character is '\0'.
David
@Andrew Morton akpm@linux-foundation.org,
Hi Andrew, I noticed you have addedthe patches to your mm-new branch, Let me know if you prefer the "%zu%c" enhancement in a new version.
David Laight david.laight.linux@gmail.com wrote:
Maybe you could use "%zu%c" and check the count is 1 - but I bet some static checker won't like that.
Yes, that would be stronger, since it would reject trailing garbage. But for a selftest this is probably sufficient: switching to size_t and parsing with "%zu" already avoids the int truncation issue.
Have you checked at what does sscanf() does with an overlong digit string? I'd guess that it just processes all the digits and then masks the result to fix (like the kernel one does).
It will truncate the number to the size SIZE_MAX.
From my test:
# ./write_to_hugetlbfs -m 0 -s 99999999999999999999999999 -p /mnt/huge/test -o Writing to this path: /mnt/huge/test Writing this size: 18446744073709551615 <---------- SIZE_MAX Populating. Not writing to memory. Using method=0 Shared mapping. RESERVE mapping. Allocating using HUGETLBFS. write_to_hugetlbfs: Error mapping the file: Invalid argument
It reality scanf() is 'not the function you are lookign for'.
IIRC the 'SUS' (used to) say that this was absolutely fine for command line parsing for 'standard utilities'.
It is best to use strtoul() and check the 'end' character is '\0'.
Hmm, that sounds like we need to go back to the patch V1 [1] method. But I am not sure, @Andrew Morton, do you think so?
--- a/tools/testing/selftests/mm/write_to_hugetlbfs.c +++ b/tools/testing/selftests/mm/write_to_hugetlbfs.c @@ -86,10 +86,17 @@ int main(int argc, char **argv) while ((c = getopt(argc, argv, "s:p:m:owlrn")) != -1) { switch (c) { case 's': - if (sscanf(optarg, "%zu", &size) != 1) { - perror("Invalid -s."); + char *end = NULL; + unsigned long tmp = strtoul(optarg, &end, 10); + if (errno || end == optarg || *end != '\0') { + perror("Invalid -s size"); exit_usage(); } + if (tmp == 0) { + perror("size not found"); + exit_usage(); + } + size = (size_t)tmp; break; case 'p':
[1] https://lore.kernel.org/linux-kselftest/20251220111645.2246009-3-liwang@redh...
-- Regards, Li Wang
linux-kselftest-mirror@lists.linaro.org
-
David Laight -
Li Wang