linux-kernel - [PATCH] kunit/fortify: Fix memcmp() test to be amplitude agnostic

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Date: Sat, 18 May 2024 11:40:23 -0700
From: Kees Cook <keescook@...omium.org>
To: linux-hardening@...r.kernel.org
Cc: Kees Cook <keescook@...omium.org>,
	Nathan Chancellor <nathan@...nel.org>,
	linux-kernel@...r.kernel.org
Subject: [PATCH] kunit/fortify: Fix memcmp() test to be amplitude agnostic

When memcmp() returns a non-zero value, only the signed bit has any
meaning. The actual value may differ between implementations.

Reported-by: Nathan Chancellor <nathan@...nel.org>
Closes: https://github.com/ClangBuiltLinux/linux/issues/2025
Tested-by: Nathan Chancellor <nathan@...nel.org>
Signed-off-by: Kees Cook <keescook@...omium.org>
---
Cc: linux-hardening@...r.kernel.org
---
 lib/fortify_kunit.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/fortify_kunit.c b/lib/fortify_kunit.c
index d2377e00caab..39da5b3bc649 100644
--- a/lib/fortify_kunit.c
+++ b/lib/fortify_kunit.c
@@ -990,7 +990,7 @@ static void fortify_test_memcmp(struct kunit *test)
 	KUNIT_ASSERT_EQ(test, memcmp(one, two, one_len), 0);
 	KUNIT_EXPECT_EQ(test, fortify_read_overflows, 0);
 	/* Still in bounds, but no longer matching. */
-	KUNIT_ASSERT_EQ(test, memcmp(one, two, one_len + 1), -32);
+	KUNIT_ASSERT_LT(test, memcmp(one, two, one_len + 1), 0);
 	KUNIT_EXPECT_EQ(test, fortify_read_overflows, 0);
 
 	/* Catch too-large ranges. */
-- 
2.34.1