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 10:45:12 -0500 |
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On 2/12/20 10:21 AM, Stephen Smalley wrote: > 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.
Also, the fact that your denials are showing up in user_systemd_t suggests that something is off in your policy or userspace/distro; I assume that is a domain type for the systemd --user instance, but your shell and commands shouldn't be running in that domain (user_t would be more appropriate for that).
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