From: Arnaldo Carvalho de Melo <acme@kernel.org>
To: "Lubashev, Igor" <ilubashe@akamai.com>
Cc: Mathieu Poirier <mathieu.poirier@linaro.org>,
Suzuki K Poulose <suzuki.poulose@arm.com>,
Peter Zijlstra <peterz@infradead.org>,
Alexey Budankov <alexey.budankov@linux.intel.com>,
Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Ingo Molnar <mingo@redhat.com>,
Namhyung Kim <namhyung@kernel.org>,
James Morris <jmorris@namei.org>, Jiri Olsa <jolsa@redhat.com>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH v3 2/4] perf: Use CAP_SYS_ADMIN with perf_event_paranoid checks
Date: Tue, 13 Aug 2019 10:20:23 -0300 [thread overview]
Message-ID: <20190813132023.GA12299@kernel.org> (raw)
In-Reply-To: <735aabdfa76f4435bdaff2c63d566044@usma1ex-dag1mb6.msg.corp.akamai.com>
Em Mon, Aug 12, 2019 at 10:33:07PM +0000, Lubashev, Igor escreveu:
> On Mon, August 12, 2019 at 4:16 PM Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com> wrote:
> > Em Mon, Aug 12, 2019 at 05:01:34PM -0300, Arnaldo Carvalho de Melo
> > escreveu:
> > > Em Wed, Aug 07, 2019 at 10:44:15AM -0400, Igor Lubashev escreveu:
> > > > +++ b/tools/perf/util/evsel.c
> > > > @@ -279,7 +279,7 @@ struct evsel *perf_evsel__new_idx(struct
> > > > perf_event_attr *attr, int idx)
> > >
> > > > static bool perf_event_can_profile_kernel(void)
> > > > {
> > > > - return geteuid() == 0 || perf_event_paranoid() == -1;
> > > > + return perf_event_paranoid_check(-1);
> > > > }
> > >
> > > While looking at your changes I think the pre-existing code is wrong,
> > > i.e. the check in sys_perf_event_open(), in the kernel is:
> > >
> > > if (!attr.exclude_kernel) {
> > > if (perf_paranoid_kernel() && !capable(CAP_SYS_ADMIN))
> > > return -EACCES;
> > > }
> > >
> > > And:
> > >
> > > static inline bool perf_paranoid_kernel(void) {
> > > return sysctl_perf_event_paranoid > 1; }
> > >
> > > So we have to change that perf_event_paranoit_check(-1) to pass 1
> > > instead?
>
> Indeed. This seems right. It was a pre-existing problem.
>
>
> > > bool perf_event_paranoid_check(int max_level) {
> > > return perf_cap__capable(CAP_SYS_ADMIN) ||
> > > perf_event_paranoid() <= max_level; }
> > >
> > > Also you defined perf_cap__capable(anything) as:
> > >
> > > #ifdef HAVE_LIBCAP_SUPPORT
> > >
> > > #include <sys/capability.h>
> > >
> > > bool perf_cap__capable(cap_value_t cap);
> > >
> > > #else
> > >
> > > static inline bool perf_cap__capable(int cap __maybe_unused)
> > > {
> > > return false;
> > > }
> > >
> > > #endif /* HAVE_LIBCAP_SUPPORT */
> > >
> > >
> > > I think we should have:
> > >
> > > #else
> > >
> > > static inline bool perf_cap__capable(int cap __maybe_unused) {
> > > return geteuid() == 0;
> > > }
> > >
> > > #endif /* HAVE_LIBCAP_SUPPORT */
> > >
> > > Right?
>
> You can have EUID==0 and not have CAP_SYS_ADMIN, though this would be rare in practice. I did not to use EUID in leu of libcap, since kernel does not do so, and therefore it seemed a bit misleading. But this is a slight matter of taste, and I do not see a problem with choosing to fall back to EUID -- the kernel will do the right thing anyway.
>
> Now, if I were pedantic, I'd say that to use geteuid(), you need to #include <unistd.h> .
Right, and that is how I did it :-)
[acme@seventh perf]$ cat tools/perf/util/cap.h
/* SPDX-License-Identifier: GPL-2.0 */
#ifndef __PERF_CAP_H
#define __PERF_CAP_H
#include <stdbool.h>
#include <linux/capability.h>
#include <linux/compiler.h>
#ifdef HAVE_LIBCAP_SUPPORT
#include <sys/capability.h>
bool perf_cap__capable(cap_value_t cap);
#else
#include <unistd.h>
#include <sys/types.h>
static inline bool perf_cap__capable(int cap __maybe_unused)
{
return geteuid() == 0;
}
#endif /* HAVE_LIBCAP_SUPPORT */
#endif /* __PERF_CAP_H */
[acme@seventh perf]$
>
> > > So I am removing the introduction of perf_cap__capable() from the
> > > first patch you sent, leaving it with _only_ the feature detection
> > > part, using that feature detection to do anything is then moved to a
> > > separate patch, after we finish this discussion about what we should
> > > fallback to when libcap-devel isn't available, i.e. we should use the
> > > previous checks, etc.
> >
> > So, please take a look at the tmp.perf/cap branch in my git repo:
> >
> > https://git.kernel.org/pub/scm/linux/kernel/git/acme/linux.git/log/?h=tmp.p
> > erf/cap
> >
> > I split the patch and made perf_cap__capable() fallback to 'return
> > geteuid() == 0;' when libcap-devel isn't available, i.e. keep the checks made
> > prior to your patchset.
>
> Thank you. And thanks for updating "make_minimal".
Ok!
> >
> > Jiri, can I keep your Acked-by?
> >
> > - Arnaldo
--
- Arnaldo
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next prev parent reply other threads:[~2019-08-13 13:20 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-07 14:44 [PATCH v3 0/4] perf: Use capabilities instead of uid and euid Igor Lubashev
2019-08-07 14:44 ` [PATCH v3 1/4] perf: Add capability-related utilities Igor Lubashev
2019-08-12 19:43 ` Arnaldo Carvalho de Melo
2019-08-07 14:44 ` [PATCH v3 2/4] perf: Use CAP_SYS_ADMIN with perf_event_paranoid checks Igor Lubashev
2019-08-12 20:01 ` Arnaldo Carvalho de Melo
2019-08-12 20:15 ` Arnaldo Carvalho de Melo
2019-08-12 22:33 ` Lubashev, Igor
2019-08-13 13:20 ` Arnaldo Carvalho de Melo [this message]
2019-08-07 14:44 ` [PATCH v3 3/4] perf: Use CAP_SYSLOG with kptr_restrict checks Igor Lubashev
2019-08-14 18:04 ` Mathieu Poirier
2019-08-14 18:48 ` Arnaldo Carvalho de Melo
2019-08-14 18:52 ` Arnaldo Carvalho de Melo
2019-08-14 20:02 ` Lubashev, Igor
2019-08-15 15:01 ` Mathieu Poirier
2019-08-15 20:16 ` Mathieu Poirier
2019-08-15 21:42 ` Arnaldo Carvalho de Melo
2019-08-19 16:51 ` Mathieu Poirier
2019-08-19 22:22 ` Lubashev, Igor
2019-08-20 16:57 ` Mathieu Poirier
2019-08-20 17:13 ` Arnaldo Carvalho de Melo
2019-08-27 1:58 ` Lubashev, Igor
2019-08-15 22:27 ` Lubashev, Igor
2019-08-07 14:44 ` [PATCH v3 4/4] perf: Use CAP_SYS_ADMIN instead of euid==0 with ftrace Igor Lubashev
2019-08-12 20:22 ` Arnaldo Carvalho de Melo
2019-08-12 20:27 ` Arnaldo Carvalho de Melo
2019-08-12 20:29 ` Arnaldo Carvalho de Melo
2019-08-12 21:42 ` Mathieu Poirier
2019-08-13 13:23 ` Arnaldo Carvalho de Melo
2019-08-13 16:35 ` Mathieu Poirier
2019-08-12 9:13 ` [PATCH v3 0/4] perf: Use capabilities instead of uid and euid Jiri Olsa
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