On 21.01.2020 17:43, Stephen Smalley wrote: > On 1/20/20 6:23 AM, Alexey Budankov wrote: >> >> Introduce CAP_PERFMON capability designed to secure system performance >> monitoring and observability operations so that CAP_PERFMON would assist >> CAP_SYS_ADMIN capability in its governing role for perf_events, i915_perf >> and other performance monitoring and observability subsystems. >> >> CAP_PERFMON intends to harden system security and integrity during system >> performance monitoring and observability operations by decreasing attack >> surface that is available to a CAP_SYS_ADMIN privileged process [1]. >> Providing access to system performance monitoring and observability >> operations under CAP_PERFMON capability singly, without the rest of >> CAP_SYS_ADMIN credentials, excludes chances to misuse the credentials and >> makes operation more secure. >> >> CAP_PERFMON intends to take over CAP_SYS_ADMIN credentials related to >> system performance monitoring and observability operations and balance >> amount of CAP_SYS_ADMIN credentials following the recommendations in the >> capabilities man page [1] for CAP_SYS_ADMIN: "Note: this capability is >> overloaded; see Notes to kernel developers, below." >> >> Although the software running under CAP_PERFMON can not ensure avoidance >> of related hardware issues, the software can still mitigate these issues >> following the official embargoed hardware issues mitigation procedure [2]. >> The bugs in the software itself could be fixed following the standard >> kernel development process [3] to maintain and harden security of system >> performance monitoring and observability operations. >> >> [1] http://man7.org/linux/man-pages/man7/capabilities.7.html >> [2] https://www.kernel.org/doc/html/latest/process/embargoed-hardware-issues.html >> [3] https://www.kernel.org/doc/html/latest/admin-guide/security-bugs.html >> >> Signed-off-by: Alexey Budankov <alexey.budankov@xxxxxxxxxxxxxxx> >> --- >> include/linux/capability.h | 12 ++++++++++++ >> include/uapi/linux/capability.h | 8 +++++++- >> security/selinux/include/classmap.h | 4 ++-- >> 3 files changed, 21 insertions(+), 3 deletions(-) >> >> diff --git a/include/linux/capability.h b/include/linux/capability.h >> index ecce0f43c73a..8784969d91e1 100644 >> --- a/include/linux/capability.h >> +++ b/include/linux/capability.h >> @@ -251,6 +251,18 @@ extern bool privileged_wrt_inode_uidgid(struct user_namespace *ns, const struct >> extern bool capable_wrt_inode_uidgid(const struct inode *inode, int cap); >> extern bool file_ns_capable(const struct file *file, struct user_namespace *ns, int cap); >> extern bool ptracer_capable(struct task_struct *tsk, struct user_namespace *ns); >> +static inline bool perfmon_capable(void) >> +{ >> + struct user_namespace *ns = &init_user_ns; >> + >> + if (ns_capable_noaudit(ns, CAP_PERFMON)) >> + return ns_capable(ns, CAP_PERFMON); >> + >> + if (ns_capable_noaudit(ns, CAP_SYS_ADMIN)) >> + return ns_capable(ns, CAP_SYS_ADMIN); >> + >> + return false; >> +} > > Why _noaudit()? Normally only used when a permission failure is non-fatal to the operation. Otherwise, we want the audit message. Some of ideas from v4 review. Well, on the second sight, it defenitly should be logged for CAP_SYS_ADMIN. Probably it is not so fatal for CAP_PERFMON, but personally I would unconditionally log it for CAP_PERFMON as well. Good catch, thank you. ~Alexey
