Re: [PATCH 0/2] selftests/seccomp: Report event mismatches more clearly

[Eric W. Biederman]

Kees Cook <keescook@xxxxxxxxxxxx> writes:

> On Wed, Nov 03, 2021 at 01:37:51PM -0500, Eric W. Biederman wrote:
>> Kees Cook <keescook@xxxxxxxxxxxx> writes:
>> 
>> > Hi,
>> >
>> > This expands the seccomp selftests slightly to add additional debug
>> > reporting detail and a new "immediate fatal SIGSYS under tracing" test.
>> > I expect to be taking these via my seccomp tree.
>> 
>> Acked-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
>> 
>> I am a little fuzzy on the details but I understand what and why
>> you are testing (I broken it).  So this is my 10,000 foot ack.
>
> Thanks! Yeah, and the other tests did catch it, but it was kind of a
> "side effect", so I added the specific "direct" case where it can be
> seen more clearly.

Hey.  Did you happen to understand the bit about racing with sigaction?

As much as I care about not braking ptrace.  What really decided me was
the on SA_IMMUTABLE was closing the race with sigaction changing the
signal handler.  Especially for something like seccomp.

It is a race so probably very fickle to write a test for, but if we can
figure out how to write a reliable test I expect it will be a good idea.
Do you have any ideas?

I am concerned there is some threaded program somewhere using seccomp
that is allowed to call sigaction, can use sigaction to keep from
being killed (before I send the fix to Linus). 

Eric