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 12:09:27 -0500 |
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On 2/12/20 11:56 AM, Alexey Budankov wrote: > > > On 12.02.2020 18:45, Stephen Smalley wrote: >> 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). > > It is user_t for local terminal session: > ps -Z > LABEL PID TTY TIME CMD > user_u:user_r:user_t 11317 pts/9 00:00:00 bash > user_u:user_r:user_t 11796 pts/9 00:00:00 ps > > For local terminal root session: > ps -Z > LABEL PID TTY TIME CMD > user_u:user_r:user_su_t 2926 pts/3 00:00:00 bash > user_u:user_r:user_su_t 10995 pts/3 00:00:00 ps > > For remote ssh session: > ps -Z > LABEL PID TTY TIME CMD > user_u:user_r:user_t 7540 pts/8 00:00:00 ps > user_u:user_r:user_systemd_t 8875 pts/8 00:00:00 bash
That's a bug in either your policy or your userspace/distro integration. In any event, unless user_systemd_t is allowed all capability2 permissions by your policy, you should see the denials if CAP_PERFMON is set in the effective capability set of the process.
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