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Date: Thu, 10 Oct 2019 19:09:49 +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 11:13:33AM -0400, Joel Fernandes wrote:
> On Thu, Oct 10, 2019 at 10:12:51AM +0200, Peter Zijlstra wrote:
> > +static inline int perf_allow_tracepoint(struct perf_event_attr *attr)
> > {
> > - return sysctl_perf_event_paranoid > 1;
> > + if (sysctl_perf_event_paranoid > -1 && !capable(CAP_SYS_ADMIN))
> > + return -EPERM;
> > +
>
> Here the sysctl check of > -1 also is now coupled with a CAP_SYS_ADMIN check.
> However..
>
> > + return security_perf_event_open(attr, PERF_SECURITY_TRACEPOINT);
>
> > }
> >
> > --- a/kernel/events/core.c
> > +++ b/kernel/events/core.c
> > @@ -5862,14 +5859,8 @@ static int perf_mmap(struct file *file,
> > lock_limit >>= PAGE_SHIFT;
> > locked = atomic64_read(&vma->vm_mm->pinned_vm) + extra;
> >
> > - if (locked > lock_limit) {
> > - if (perf_paranoid_tracepoint_raw() && !capable(CAP_IPC_LOCK)) {
> > - ret = -EPERM;
> > - goto unlock;
> > - }
> > -
> > - ret = security_perf_event_open(&event->attr,
> > - PERF_SECURITY_TRACEPOINT);
> > + if (locked > lock_limit && !capable(CAP_IPC_LOCK)) {
> > + ret = perf_allow_tracepoint(&event->attr);
>
> In previous code, this check did not involve a check for CAP_SYS_ADMIN.
>
> I am Ok with adding the CAP_SYS_ADMIN check as well which does make sense to
> me for tracepoint access. But it is still a change in the logic so I wanted
> to bring it up.
>
> Let me know any other thoughts and then I'll post a new patch.
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")
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