linux-kernel - Re: [PATCH v1] perf/core: take over CAP_SYS_PTRACE creds to CAP

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Date:   Thu, 6 Aug 2020 09:16:48 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Alexey Budankov <alexey.budankov@...ux.intel.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Andi Kleen <ak@...ux.intel.com>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1] perf/core: take over CAP_SYS_PTRACE creds to
 CAP_PERFMON cap

Em Wed, Aug 05, 2020 at 10:56:56AM +0300, Alexey Budankov escreveu:
> 
> Open access to per-process monitoring for CAP_PERFMON only
> privileged processes [1]. Extend ptrace_may_access() check
> in perf_events subsystem with perfmon_capable() to simplify
> user experience and make monitoring more secure by reducing
> attack surface.


Acked-by: Arnaldo Carvalho de Melo <acme@...hat.com>

Peter, can you pick up this one? You said it was ok last time we
discussed this.

- Arnaldo
 
> [1] https://lore.kernel.org/lkml/7776fa40-6c65-2aa6-1322-eb3a01201000@linux.intel.com/
> 
> Signed-off-by: Alexey Budankov <alexey.budankov@...ux.intel.com>
> ---
>  kernel/events/core.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 856d98c36f56..f50d528af444 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -11587,7 +11587,7 @@ SYSCALL_DEFINE5(perf_event_open,
>  			goto err_task;
>  
>  		/*
> -		 * Reuse ptrace permission checks for now.
> +		 * Preserve ptrace permission check for backwards compatibility.
>  		 *
>  		 * We must hold exec_update_mutex across this and any potential
>  		 * perf_install_in_context() call for this new event to
> @@ -11595,7 +11595,7 @@ SYSCALL_DEFINE5(perf_event_open,
>  		 * perf_event_exit_task() that could imply).
>  		 */
>  		err = -EACCES;
> -		if (!ptrace_may_access(task, PTRACE_MODE_READ_REALCREDS))
> +		if (!perfmon_capable() && !ptrace_may_access(task, PTRACE_MODE_READ_REALCREDS))
>  			goto err_cred;
>  	}
>  
> -- 
> 2.24.1
> 

-- 

- Arnaldo