linux-kernel - Re: [PATCH] selinux: add tracepoint on denials

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Message-ID: <def030b4-91c3-4aa1-e8ad-e3797688d18d@sony.com>
Date:   Thu, 30 Jul 2020 10:03:41 +0200
From:   peter enderborg <peter.enderborg@...y.com>
To:     Thiébaud Weksteen <tweek@...gle.com>,
        Paul Moore <paul@...l-moore.com>
CC:     Steven Rostedt <rostedt@...dmis.org>,
        Stephen Smalley <stephen.smalley.work@...il.com>,
        Nick Kralevich <nnk@...gle.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Eric Paris <eparis@...isplace.org>,
        Ingo Molnar <mingo@...hat.com>,
        Mauro Carvalho Chehab <mchehab+huawei@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Rob Herring <robh@...nel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        SElinux list <selinux@...r.kernel.org>
Subject: Re: [PATCH] selinux: add tracepoint on denials

On 7/28/20 6:02 PM, Thiébaud Weksteen wrote:
> On Tue, Jul 28, 2020 at 5:12 PM Paul Moore <paul@...l-moore.com> 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.