Messages in this thread | | | Subject | Re: [PATCH v5 01/10] capabilities: introduce CAP_PERFMON to kernel and user space | From | Stephen Smalley <> | Date | Wed, 12 Feb 2020 10:21:22 -0500 |
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On 2/12/20 8:53 AM, Alexey Budankov wrote: > On 12.02.2020 16:32, Stephen Smalley wrote: >> On 2/12/20 3:53 AM, Alexey Budankov wrote: >>> Hi Stephen, >>> >>> On 22.01.2020 17:07, Stephen Smalley wrote: >>>> On 1/22/20 5:45 AM, Alexey Budankov wrote: >>>>> >>>>> On 21.01.2020 21:27, Alexey Budankov wrote: >>>>>> >>>>>> On 21.01.2020 20:55, Alexei Starovoitov wrote: >>>>>>> On Tue, Jan 21, 2020 at 9:31 AM Alexey Budankov >>>>>>> <alexey.budankov@linux.intel.com> wrote: >>>>>>>> >>>>>>>> >>>>>>>> On 21.01.2020 17:43, Stephen Smalley wrote: >>>>>>>>> On 1/20/20 6:23 AM, Alexey Budankov wrote: >>>>>>>>>> >>> <SNIP> >>>>>>>>>> Introduce CAP_PERFMON capability designed to secure system performance >>>>>>>>> >>>>>>>>> Why _noaudit()? Normally only used when a permission failure is non-fatal to the operation. Otherwise, we want the audit message. >>>>> >>>>> So far so good, I suggest using the simplest version for v6: >>>>> >>>>> static inline bool perfmon_capable(void) >>>>> { >>>>> return capable(CAP_PERFMON) || capable(CAP_SYS_ADMIN); >>>>> } >>>>> >>>>> It keeps the implementation simple and readable. The implementation is more >>>>> performant in the sense of calling the API - one capable() call for CAP_PERFMON >>>>> privileged process. >>>>> >>>>> Yes, it bloats audit log for CAP_SYS_ADMIN privileged and unprivileged processes, >>>>> but this bloating also advertises and leverages using more secure CAP_PERFMON >>>>> based approach to use perf_event_open system call. >>>> >>>> I can live with that. We just need to document that when you see both a CAP_PERFMON and a CAP_SYS_ADMIN audit message for a process, try only allowing CAP_PERFMON first and see if that resolves the issue. We have a similar issue with CAP_DAC_READ_SEARCH versus CAP_DAC_OVERRIDE. >>> >>> I am trying to reproduce this double logging with CAP_PERFMON. >>> I am using the refpolicy version with enabled perf_event tclass [1], in permissive mode. >>> When running perf stat -a I am observing this AVC audit messages: >>> >>> type=AVC msg=audit(1581496695.666:8691): avc: denied { open } for pid=2779 comm="perf" scontext=user_u:user_r:user_systemd_t tcontext=user_u:user_r:user_systemd_t tclass=perf_event permissive=1 >>> type=AVC msg=audit(1581496695.666:8691): avc: denied { kernel } for pid=2779 comm="perf" scontext=user_u:user_r:user_systemd_t tcontext=user_u:user_r:user_systemd_t tclass=perf_event permissive=1 >>> type=AVC msg=audit(1581496695.666:8691): avc: denied { cpu } for pid=2779 comm="perf" scontext=user_u:user_r:user_systemd_t tcontext=user_u:user_r:user_systemd_t tclass=perf_event permissive=1 >>> type=AVC msg=audit(1581496695.666:8692): avc: denied { write } for pid=2779 comm="perf" scontext=user_u:user_r:user_systemd_t tcontext=user_u:user_r:user_systemd_t tclass=perf_event permissive=1 >>> >>> However there is no capability related messages around. I suppose my refpolicy should >>> be modified somehow to observe capability related AVCs. >>> >>> Could you please comment or clarify on how to enable caps related AVCs in order >>> to test the concerned logging. >> >> The new perfmon permission has to be defined in your policy; you'll have a message in dmesg about "Permission perfmon in class capability2 not defined in policy.". You can either add it to the common cap2 definition in refpolicy/policy/flask/access_vectors and rebuild your policy or extract your base module as CIL, add it there, and insert the updated module. > > Yes, I already have it like this: > common cap2 > { > <------>mac_override<--># unused by SELinux > <------>mac_admin > <------>syslog > <------>wake_alarm > <------>block_suspend > <------>audit_read > <------>perfmon > } > > dmesg stopped reporting perfmon as not defined but audit.log still doesn't report CAP_PERFMON denials. > BTW, audit even doesn't report CAP_SYS_ADMIN denials, however perfmon_capable() does check for it.
Some denials may be silenced by dontaudit rules; semodule -DB will strip those and semodule -B will restore them. Other possibility is that the process doesn't have CAP_PERFMON in its effective set and therefore never reaches SELinux at all; denied first by the capability module.
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