linux-kernel - Re: [PATCH RFC] perf_event: Add support for LSM and SELinux checks

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Message-ID: <20191011070543.GV2328@hirez.programming.kicks-ass.net>
Date:   Fri, 11 Oct 2019 09:05:43 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Joel Fernandes <joel@...lfernandes.org>
Cc:     linux-kernel@...r.kernel.org, rostedt@...dmis.org,
        primiano@...gle.com, rsavitski@...gle.com, jeffv@...gle.com,
        kernel-team@...roid.com, Alexei Starovoitov <ast@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        bpf@...r.kernel.org, Daniel Borkmann <daniel@...earbox.net>,
        Ingo Molnar <mingo@...hat.com>,
        James Morris <jmorris@...ei.org>, Jiri Olsa <jolsa@...hat.com>,
        Kees Cook <keescook@...omium.org>,
        linux-security-module@...r.kernel.org,
        Matthew Garrett <matthewgarrett@...gle.com>,
        Namhyung Kim <namhyung@...nel.org>, selinux@...r.kernel.org,
        Song Liu <songliubraving@...com>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        Yonghong Song <yhs@...com>
Subject: Re: [PATCH RFC] perf_event: Add support for LSM and SELinux checks

On Thu, Oct 10, 2019 at 02:31:14PM -0400, Joel Fernandes wrote:
> On Thu, Oct 10, 2019 at 07:09:49PM +0200, Peter Zijlstra wrote:

> > Yes, I did notice, I found it weird.
> > 
> > If you have CAP_IPC_LIMIT you should be able to bust mlock memory
> > limits, so I don't see why we should further relate that to paranoid.
> > 
> > The way I wrote it, we also allow to bust the limit if we have disabled
> > all paranoid checks. Which makes some sense I suppose.
> > 
> > The original commit is this:
> > 
> >   459ec28ab404 ("perf_counter: Allow mmap if paranoid checks are turned off")
> 
> I am thinking we can just a new function perf_is_paranoid() that has nothing
> to do with the CAP_SYS_ADMIN check and doesn't have tracepoint wording:
> 
> static inline int perf_is_paranoid(void)
> {
> 	return sysctl_perf_event_paranoid > -1;
> }
> 
> And then call that from the mmap() code:
> if (locked > lock_limit && perf_is_paranoid() && !capable(CAP_IPC_LOCK)) {
> 	return -EPERM;
> }
> 
> I don't think we need to add selinux security checks here since we are
> already adding security checks earlier in mmap(). This will make the code and
> its intention more clear and in line with the commit 459ec28ab404 you
> mentioned. Thoughts?

Mostly that I'm confused by the current code ;-)

Like I said, CAP_IPC_LIMIT on its own should already allow busting the
limit, I don't really see why we should make it conditional on paranoid.

But if you want to preserve behaviour (arguably a sane thing for your
patch) then yes, feel free to do as you propose.