Re: [PATCH] perf: Check permission only for parent tracepoint event

[Alexander Yarygin]

At Wed, 16 Jul 2014 14:33:29 +0200,
Jiri Olsa wrote:
> 
> There's no need to check cloned event's permission once the
> parent was already checked.
> 
> Also the code is checking 'current' process permissions, which
> is not owner process for cloned events, thus could end up with
> wrong permission check result.
> 
> Reported-by: Alexander Yarygin <yarygin@xxxxxxxxxxxxxxxxxx>
> Cc: Alexander Yarygin <yarygin@xxxxxxxxxxxxxxxxxx>
> Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
> Cc: Corey Ashford <cjashfor@xxxxxxxxxxxxxxxxxx>
> Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: Paul Mackerras <paulus@xxxxxxxxx>
> Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
> Link: http://lkml.kernel.org/r/1405079782-8139-1-git-send-email-jolsa@xxxxxxxxxx
> Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
> ---
>  kernel/trace/trace_event_perf.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/kernel/trace/trace_event_perf.c b/kernel/trace/trace_event_perf.c
> index 5d12bb407b44..4b9c114ee9de 100644
> --- a/kernel/trace/trace_event_perf.c
> +++ b/kernel/trace/trace_event_perf.c
> @@ -30,6 +30,18 @@ static int perf_trace_event_perm(struct ftrace_event_call *tp_event,
>  			return ret;
>  	}
> 
> +	/*
> +	 * We checked and allowed to create parent,
> +	 * allow children without checking.
> +	 */
> +	if (p_event->parent)
> +		return 0;
> +
> +	/*
> +	 * It's ok to check current process (owner) permissions in here,
> +	 * because code below is called only via perf_event_open syscall.
> +	 */
> +
>  	/* The ftrace function trace is allowed only for root. */
>  	if (ftrace_event_is_function(tp_event)) {
>  		if (perf_paranoid_tracepoint_raw() && !capable(CAP_SYS_ADMIN))
> -- 
> 1.8.3.1
> 

Tested-by: Alexander Yarygin <yarygin@xxxxxxxxxxxxxxxxxx>

Thanks.

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