| Message ID | 1475626874-22949-1-git-send-email-john.stultz@linaro.org |
|---|---|
| State | Superseded |
| Headers | show |
On Tue, Oct 4, 2016 at 5:38 PM, Serge E. Hallyn <serge@hallyn.com> wrote: > Quoting John Stultz (john.stultz@linaro.org): >> So this patch, as suggested by Tejun, simply adds a new process >> capability flag (CAP_CGROUP_MIGRATE_TASK), and uses it when checking > > So realistically, what all can this mean? Freezing tasks, changing > cpu/memory limits, changing network and disk throughput, forbid forking, > and (most importantly) forbid access to certain devices. > > I think that's all ok. (And we still separately check for inode write > perms.) Sounds good. > If anything I'd say the GLOBAL_ROOT_UID check could be taken out since > otherwise a host-root task effectively cannot drop this capability. Is this ok to leave for a separate patch? > Acked-by: Serge Hallyn <serge@hallyn.com> Thanks for the review! Unless there's other feedback, I'll sit on this until the merge window is over and then resubmit for consideration for 4.10. thanks -john
diff --git a/include/uapi/linux/capability.h b/include/uapi/linux/capability.h index 49bc062..e199ea0 100644 --- a/include/uapi/linux/capability.h +++ b/include/uapi/linux/capability.h @@ -349,8 +349,11 @@ struct vfs_cap_data { #define CAP_AUDIT_READ 37 +/* Allow migrating tasks between cgroups */ -#define CAP_LAST_CAP CAP_AUDIT_READ +#define CAP_CGROUP_MIGRATE_TASK 38 + +#define CAP_LAST_CAP CAP_CGROUP_MIGRATE_TASK #define cap_valid(x) ((x) >= 0 && (x) <= CAP_LAST_CAP) diff --git a/kernel/cgroup.c b/kernel/cgroup.c index 9ba28310..a318956 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -2847,7 +2847,8 @@ static int cgroup_procs_write_permission(struct task_struct *task, */ if (!uid_eq(cred->euid, GLOBAL_ROOT_UID) && !uid_eq(cred->euid, tcred->uid) && - !uid_eq(cred->euid, tcred->suid)) + !uid_eq(cred->euid, tcred->suid) && + !ns_capable(tcred->user_ns, CAP_CGROUP_MIGRATE_TASK)) ret = -EACCES; if (!ret && cgroup_on_dfl(dst_cgrp)) {
This patch adds CAP_GROUP_MIGRATE_TASK and logic to allows a process to migrate other tasks between cgroups. In Android (where this feature originated), the ActivityManager tracks various application states (TOP_APP, FOREGROUND, BACKGROUND, SYSTEM, etc), and then as applications change states, the SchedPolicy logic will migrate the application tasks between different cgroups used to control the different application states (for example, there is a background cpuset cgroup which can limit background tasks to stay on one low-power cpu, and the bg_non_interactive cpuctrl cgroup can then further limit those background tasks to a small percentage of that one cpu's cpu time). However, for security reasons, Android doesn't want to make the system_server (the process that runs the ActivityManager and SchedPolicy logic), run as root. So in the Android common.git kernel, they have some logic to allow cgroups to loosen their permissions so CAP_SYS_NICE tasks can migrate other tasks between cgroups. The approach taken there overloads CAP_SYS_NICE a bit much, and is maybe more complicated then needed. So this patch, as suggested by Tejun, simply adds a new process capability flag (CAP_CGROUP_MIGRATE_TASK), and uses it when checking if a task can migrate other tasks between cgroups. I've tested this with AOSP master (though its a bit hacked in as I still need to properly get the selinux bits aware of the new capability bit) with selinux set to permissive and it seems to be working well. Thouhts and feedback would be appreciated! Cc: Tejun Heo <tj@kernel.org> Cc: Li Zefan <lizefan@huawei.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: cgroups@vger.kernel.org Cc: Android Kernel Team <kernel-team@android.com> Cc: Rom Lemarchand <romlem@android.com> Cc: Colin Cross <ccross@android.com> Cc: Dmitry Shmidt <dimitrysh@google.com> Cc: Todd Kjos <tkjos@google.com> Cc: Christian Poetzsch <christian.potzsch@imgtec.com> Cc: Amit Pundir <amit.pundir@linaro.org> Cc: Serge E. Hallyn <serge@hallyn.com> Signed-off-by: John Stultz <john.stultz@linaro.org> --- include/uapi/linux/capability.h | 5 ++++- kernel/cgroup.c | 3 ++- 2 files changed, 6 insertions(+), 2 deletions(-) -- 1.9.1