This patch adds logic to allows a process to migrate other tasks between cgroups if they have CAP_SYS_RESOURCE. 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. I feel the approach taken there overloads CAP_SYS_NICE a bit much for non-android environments. So this patch, as suggested by Michael Kerrisk, simply adds a check for CAP_SYS_RESOURCE. I've tested this with AOSP master, and this seems to work well as Zygote and system_server already use CAP_SYS_RESOURCE. I've also submitted patches against the android-4.4 kernel to change it to use CAP_SYS_RESOURCE, and the Android developers just merged it. Thouhts and feedback would be appreciated! Cc: Tejun Heo <tj@xxxxxxxxxx> Cc: Li Zefan <lizefan@xxxxxxxxxx> Cc: Jonathan Corbet <corbet@xxxxxxx> Cc: cgroups@xxxxxxxxxxxxxxx Cc: Android Kernel Team <kernel-team@xxxxxxxxxxx> Cc: Rom Lemarchand <romlem@xxxxxxxxxxx> Cc: Colin Cross <ccross@xxxxxxxxxxx> Cc: Dmitry Shmidt <dimitrysh@xxxxxxxxxx> Cc: Todd Kjos <tkjos@xxxxxxxxxx> Cc: Christian Poetzsch <christian.potzsch@xxxxxxxxxx> Cc: Amit Pundir <amit.pundir@xxxxxxxxxx> Cc: Dmitry Torokhov <dmitry.torokhov@xxxxxxxxx> Cc: Kees Cook <keescook@xxxxxxxxxxxx> Cc: Serge E. Hallyn <serge@xxxxxxxxxx> Cc: linux-api@xxxxxxxxxxxxxxx Acked-by: Serge Hallyn <serge@xxxxxxxxxx> Signed-off-by: John Stultz <john.stultz@xxxxxxxxxx> --- v2: Renamed to just CAP_CGROUP_MIGRATE as reccomended by Tejun v3: Switched to just using CAP_SYS_RESOURCE as suggested by Michael v4: Send out properly folded down version of the patch. :P --- kernel/cgroup.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/kernel/cgroup.c b/kernel/cgroup.c index 85bc9be..866059a 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -2856,7 +2856,8 @@ 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_SYS_RESOURCE)) ret = -EACCES; if (!ret && cgroup_on_dfl(dst_cgrp)) { -- 2.7.4 -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html