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

[Peter Zijlstra <peterz@infradead.org>]

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.