Re: [PATCH v2 2/7] perf/core: open access for CAP_SYS_PERFMON privileged process

[Alexey Budankov]

On 16.12.2019 19:12, Lubashev, Igor wrote:
> On Mon, Dec 16, 2019 at 2:15 AM, Alexey Budankov <alexey.budankov@xxxxxxxxxxxxxxx> wrote:
>>
>> Open access to perf_events monitoring for CAP_SYS_PERFMON privileged
>> processes.
>> For backward compatibility reasons access to perf_events subsystem remains
>> open for CAP_SYS_ADMIN privileged processes but CAP_SYS_ADMIN usage
>> for secure perf_events monitoring is discouraged with respect to
>> CAP_SYS_PERFMON capability.
>>
>> Signed-off-by: Alexey Budankov <alexey.budankov@xxxxxxxxxxxxxxx>
>> ---
>>  include/linux/perf_event.h | 9 ++++++---
>>  1 file changed, 6 insertions(+), 3 deletions(-)
>>
>> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h index
>> 34c7c6910026..52313d2cc343 100644
>> --- a/include/linux/perf_event.h
>> +++ b/include/linux/perf_event.h
>> @@ -1285,7 +1285,8 @@ static inline int perf_is_paranoid(void)
>>
>>  static inline int perf_allow_kernel(struct perf_event_attr *attr)  {
>> -	if (sysctl_perf_event_paranoid > 1 && !capable(CAP_SYS_ADMIN))
>> +	if (sysctl_perf_event_paranoid > 1 &&
>> +	   !(capable(CAP_SYS_PERFMON) || capable(CAP_SYS_ADMIN)))
>>  		return -EACCES;
>>
>>  	return security_perf_event_open(attr, PERF_SECURITY_KERNEL); @@
>> -1293,7 +1294,8 @@ static inline int perf_allow_kernel(struct
>> perf_event_attr *attr)
>>
>>  static inline int perf_allow_cpu(struct perf_event_attr *attr)  {
>> -	if (sysctl_perf_event_paranoid > 0 && !capable(CAP_SYS_ADMIN))
>> +	if (sysctl_perf_event_paranoid > 0 &&
>> +	    !(capable(CAP_SYS_PERFMON) || capable(CAP_SYS_ADMIN)))
>>  		return -EACCES;
>>
>>  	return security_perf_event_open(attr, PERF_SECURITY_CPU); @@ -
>> 1301,7 +1303,8 @@ static inline int perf_allow_cpu(struct perf_event_attr
>> *attr)
>>
>>  static inline int perf_allow_tracepoint(struct perf_event_attr *attr)  {
>> -	if (sysctl_perf_event_paranoid > -1 && !capable(CAP_SYS_ADMIN))
>> +	if (sysctl_perf_event_paranoid > -1 &&
>> +	    !(capable(CAP_SYS_PERFMON) || capable(CAP_SYS_ADMIN)))
>>  		return -EPERM;
>>
>>  	return security_perf_event_open(attr, PERF_SECURITY_TRACEPOINT);
>> --
>> 2.20.1
> 
> Thanks.  I like the idea of CAP_SYS_PERFMON that does not require CAP_SYS_ADMIN.  It makes granting users ability to run perf a bit safer.
> 
> I see a lot of "(capable(CAP_SYS_PERFMON) || capable(CAP_SYS_ADMIN)" constructs now.  Maybe wrapping it in an " inline bool perfmon_capable()" defined somewhere (like in /include/linux/capability.h)?

Sounds reasonable, thanks!

~Alexey

> 
> - Igor
>