On Mon, Sep 07, 2026 at 04:52:46AM +0000, Chaithanya Lagisetty wrote:
> demand_paging_test parses the -d option with strtoul() and then asserts
> that the result is not negative:
>
> p.uffd_delay = strtoul(optarg, NULL, 0);
> TEST_ASSERT(p.uffd_delay >= 0, "A negative UFFD delay is not
> supported.");
>
> p.uffd_delay is a useconds_t, which is an unsigned type, so the comparison
> is always true and the assertion can never fire. GCC points this out with
> -Wtype-limits, which is enabled by -Wextra.
>
> As a result, "-d -1" is accepted and converted to a very large unsigned
> delay, causing each demand paging fault to sleep for an unexpectedly long
> time in usleep() instead of rejecting the argument up front. The return
> value of strtoul() is not validated either, so a non-numeric argument
> such as "-d abc" is silently treated as a zero delay.
>
> Use atoi_non_negative() instead. It rejects negative values, unparsable
> input, and trailing garbage. It is already used a few lines below for -v,
> and hexadecimal input keeps working because atoi_paranoid() also passes a
> base of 0 to strtol().
>
> Fixes: 0119cb365c93 ("KVM: selftests: Add configurable demand paging delay")
> Signed-off-by: Chaithanya Lagisetty <[email protected]>
> ---
> tools/testing/selftests/kvm/demand_paging_test.c | 3 +--
> 1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/tools/testing/selftests/kvm/demand_paging_test.c
> b/tools/testing/selftests/kvm/demand_paging_test.c
> index f8b3d0b68830..619a0b2be45c 100644
> --- a/tools/testing/selftests/kvm/demand_paging_test.c
> +++ b/tools/testing/selftests/kvm/demand_paging_test.c
> @@ -297,8 +297,7 @@ int main(int argc, char *argv[])
> p.single_uffd = true;
> break;
> case 'd':
> - p.uffd_delay = strtoul(optarg, NULL, 0);
> - TEST_ASSERT(p.uffd_delay >= 0, "A negative UFFD delay
> is not supported.");
> + p.uffd_delay = atoi_non_negative("UFFD delay", optarg);
> break;
> case 'b':
> guest_percpu_mem_size = parse_size(optarg);
> --
> 2.43.0
>
With this patch applied, the test fails as intended:
# ./demand_paging_test -d -1
Random seed: 0x236c0ed9
==== Test Assertion Failure ====
include/test_util.h:236: num >= 0
pid=3674565 tid=3674565 errno=0 - Success
1 0x00000000004010d0: atoi_non_negative at test_util.h:236
2 (inlined by) main at demand_paging_test.c:300
3 0x00007f907d9f05b4: ?? ??:0
4 0x00007f907d9f0667: ?? ??:0
5 0x0000000000401374: _start at ??:?
UFFD delay must be non-negative, got '-1'
Tested-by: Gautam Menghani <[email protected]>
Reviewed-by: Gautam Menghani <[email protected]>
