[PATCH] KVM: selftests: Fix the never-true negative UFFD delay check

[Chaithanya Lagisetty <nagachaithanya9911@gmail.com>]

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 <nagachaithanya9911@gmail.com>
---
 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