The clone_args structure is extensible, with the syscall passing in the
length of the structure. Inside the kernel we use copy_struct_from_user()
to read the struct but this has the unfortunate side effect of silently
accepting some overrun in the structure size providing the extra data is
all zeros. This means that we can't discover the clone3() features that
the running kernel supports by simply probing with various struct sizes.
We need to check this for the benefit of test systems which run newer
kselftests on old kernels.

Add a flag which can be set on a test to indicate that clone3() may return
-E2BIG due to the use of newer struct versions. Currently no tests need
this but it will become an issue for testing clone3() support for shadow
stacks, the support for shadow stacks is already present on x86.

Reviewed-by: Kees Cook <kees@kernel.org>
Tested-by: Kees Cook <kees@kernel.org>
Acked-by: Shuah Khan <skhan@linuxfoundation.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
---
 tools/testing/selftests/clone3/clone3.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/tools/testing/selftests/clone3/clone3.c b/tools/testing/selftests/clone3/clone3.c
index e066b201fa64eb17c55939b7cec18ac5d109613b..5b8b7d640e70132242fc6939450669acd0c534f9 100644
--- a/tools/testing/selftests/clone3/clone3.c
+++ b/tools/testing/selftests/clone3/clone3.c
@@ -39,6 +39,7 @@ struct test {
 	size_t size;
 	size_function size_function;
 	int expected;
+	bool e2big_valid;
 	enum test_mode test_mode;
 	filter_function filter;
 };
@@ -146,6 +147,11 @@ static void test_clone3(const struct test *test)
 	ksft_print_msg("[%d] clone3() with flags says: %d expected %d\n",
 			getpid(), ret, test->expected);
 	if (ret != test->expected) {
+		if (test->e2big_valid && ret == -E2BIG) {
+			ksft_print_msg("Test reported -E2BIG\n");
+			ksft_test_result_skip("%s\n", test->name);
+			return;
+		}
 		ksft_print_msg(
 			"[%d] Result (%d) is different than expected (%d)\n",
 			getpid(), ret, test->expected);

-- 
2.39.2