linux-kernel - Re: [PATCH v3 4/4] perf: Use CAP_SYS_ADMIN instead of euid==0 with ftrace

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Date:   Mon, 12 Aug 2019 15:42:17 -0600
From:   Mathieu Poirier <mathieu.poirier@...aro.org>
To:     Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
Cc:     Igor Lubashev <ilubashe@...mai.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Jiri Olsa <jolsa@...hat.com>,
        Alexey Budankov <alexey.budankov@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        James Morris <jmorris@...ei.org>
Subject: Re: [PATCH v3 4/4] perf: Use CAP_SYS_ADMIN instead of euid==0 with ftrace

On Mon, 12 Aug 2019 at 14:29, Arnaldo Carvalho de Melo
<arnaldo.melo@...il.com> wrote:
>
> Em Mon, Aug 12, 2019 at 05:27:06PM -0300, Arnaldo Carvalho de Melo escreveu:
> > Em Mon, Aug 12, 2019 at 05:22:51PM -0300, Arnaldo Carvalho de Melo escreveu:
> > > Em Wed, Aug 07, 2019 at 10:44:17AM -0400, Igor Lubashev escreveu:
> > > > @@ -281,7 +283,7 @@ static int __cmd_ftrace(struct perf_ftrace *ftrace, int argc, const char **argv)
> > > >           .events = POLLIN,
> > > >   };
> > > >
> > > > - if (geteuid() != 0) {
> > > > + if (!perf_cap__capable(CAP_SYS_ADMIN)) {
> > > >           pr_err("ftrace only works for root!\n");
> > >
> > > I guess we should update the error message too?
> > >
> >
> > I.e. I applied this as a follow up patch:
> >
> > diff --git a/tools/perf/builtin-ftrace.c b/tools/perf/builtin-ftrace.c
> > index 01a5bb58eb04..ba8b65c2f9dc 100644
> > --- a/tools/perf/builtin-ftrace.c
> > +++ b/tools/perf/builtin-ftrace.c
> > @@ -284,7 +284,12 @@ static int __cmd_ftrace(struct perf_ftrace *ftrace, int argc, const char **argv)
> >       };
> >
> >       if (!perf_cap__capable(CAP_SYS_ADMIN)) {
> > -             pr_err("ftrace only works for root!\n");
> > +             pr_err("ftrace only works for %s!\n",
> > +#ifdef HAVE_LIBCAP_SUPPORT
> > +             "users with the SYS_ADMIN capability"
> > +#else
> > +             "root"
> > +#endif
>
>                 );
>
> :-)
>
> >               return -1;
> >       }
> >
>
> I've pushed the whole set to my tmp.perf/cap branch, please chec

Please hold on before moving further - I'm getting a segmentation
fault on ARM64 that I'm still trying to figure out.

>
> - Arnaldo