Re: [PATCH v3 3/3] selftests/seccomp: Test kernel catches garbage on SECCOMP_IOCTL_NOTIF_RECV

On Sun, Dec 29, 2019 at 03:42:17PM -0800, Sargun Dhillon wrote:

On Sun, Dec 29, 2019 at 11:43 AM Christian Brauner
[off-list ref] wrote:

quoted

On Sun, Dec 29, 2019 at 11:06:25AM -0800, Sargun Dhillon wrote:

quoted

On Sun, Dec 29, 2019 at 12:14 PM Christian Brauner
[off-list ref] wrote:

quoted

Does that even work if no dup() syscall has been made and trapped?

Yes, the first check that occurs is the check which checks if
seccom_notif has been
zeroed out. This happens before any of the other work.

Ah, then sure I don't mind doing it this way. Though plumbing it
directly into TEST(user_notification_basic) like I did below seems
cleaner to me.

quoted

quoted

This looks like it would give you ENOENT...

This ioctl is a blocking ioctl. It'll block until there is a wakeup.
In this case, the wakeup
will never come, but that doesn't mean we get an ENOENT.

Yeah, but that wold mean the test will hang weirdly if it bypasses the
check. Sure it'll timeout but meh. I think I would prefer to have this
done as part of the basic test where we know that there is an event but
_shrug_.

I'd like to design the tests to not _depend_ on the timeout to catch bad
behaviors. The timeout is there for us to not break a test runner when
we forget weird corner cases.

My one worry about this is that the behaviour should be if the input
(seccomp_notif) is invalid, it should immediately bail out, whether
or not there is an event waiting. If we add it to basic_test, then
it would hide the erroneous behaviour if bailout isn't immediate.

I'm not following this paragraph. The ioctl's zero check is immediate,
so this test should fail the EXPECT (but continue to the next "correct"
ioctl) -- it's not an ASSERT (which would stop the test). I think
Christian's test might be a cleaner approach, unless I'm still missing
something here?

-- 
Kees Cook