Re: [PATCH 2/3] selftests: Fix errno checking in syscall_user_dispatch test

[Kees Cook <kees@kernel.org>]

On Tue, Feb 18, 2025 at 05:04:35PM +0100, Dmitry Vyukov wrote:
> Successful syscalls don't change errno, so checking errno is wrong
> to ensure that a syscall has failed. For example for the following
> sequence:
> 
> 	prctl(PR_SET_SYSCALL_USER_DISPATCH, op, 0x0, 0xff, 0);
> 	EXPECT_EQ(EINVAL, errno);
> 	prctl(PR_SET_SYSCALL_USER_DISPATCH, op, 0x0, 0x0, &sel);
> 	EXPECT_EQ(EINVAL, errno);
> 
> only the first syscall may fail and set errno, but the second may succeed
> and keep errno intact, and the check will falsely pass.
> Or if errno happened to be EINVAL before, even the first check may falsely
> pass.
> 
> Also use EXPECT/ASSERT consistently. Currently there is an inconsistent mix
> without obvious reasons for usage of one or another.
> 
> Signed-off-by: Dmitry Vyukov <dvyukov@google.com>

Reviewed-by: Kees Cook <kees@kernel.org>

Yeah, these all look good to me.

-- 
Kees Cook