Messages in this thread | | | From | Arnaldo Carvalho de Melo <> | Date | Mon, 12 Aug 2019 17:01:34 -0300 | Subject | Re: [PATCH v3 2/4] perf: Use CAP_SYS_ADMIN with perf_event_paranoid checks |
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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?
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?
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.
- Arnaldo
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