Re: [PATCH] selinux: add tracepoint on denials

From: peter enderborg
Date: Thu Jul 30 2020 - 04:03:48 EST

On 7/28/20 6:02 PM, ThiÃbaud Weksteen wrote:
> On Tue, Jul 28, 2020 at 5:12 PM Paul Moore <paul@xxxxxxxxxxxxxx> wrote:
>> Perhaps it would be helpful if you provided an example of how one
>> would be expected to use this new tracepoint? That would help put
>> things in the proper perspective.
> The best example is the one I provided in the commit message, that is
> using perf (or a perf equivalent), to hook onto that tracepoint.
>> Well, to be honest, the very nature of this tracepoint is duplicating
>> the AVC audit record with a focus on using perf to establish a full
>> backtrace at the expense of reduced information. At least that is how
>> it appears to me.
> I see both methods as complementary. By default, the kernel itself can
> do some reporting (i.e avc message) on which process triggered the
> denial, what was the context, etc. This is useful even in production
> and doesn't require any extra tooling.
> The case for adding this tracepoint can be seen as advanced debugging.
> That is, once an avc denial has been confirmed, a developer can use
> this tracepoint to surface the userland stacktrace. It requires more
> userland tools and symbols on the userland binaries.

I think from development view you would like to have a better
way to trap this events in userspace. One idea that I have is
is to have more outcomes from a rule. We have today allow,
dontaudit, auditallow i think it would be good to have signal sent too.
"signal-xxx-allow" for some set of signals. SIGBUS, SIGSEGV, SIGABRT maybe.

That will be a good way to pickup the problem with a debugger or generate a
a core file.

I have also done some selinux trace functions. I think they collide with this set,
but I think I can rebase them upon yours and see if they give some more functionality.

I see this functionality very much needed in some form.