CHROMIUM: cgroups: relax permissions on moving tasks between cgroups

Android expects system_server to be able to move tasks between different
cgroups/cpusets, but does not want to be running as root. Let's relax
permission check so that processes can move other tasks if they have
CAP_SYS_NICE in the affected task's user namespace.

BUG=b:31790445,chromium:647994
TEST=Boot android container, examine logcat

Change-Id: Ia919c66ab6ed6a6daf7c4cf67feb38b13b1ad09b
Signed-off-by: Dmitry Torokhov <dtor@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/394927
Reviewed-by: Ricky Zhou <rickyz@chromium.org>

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 371ee5a827e007a3cf4299c050cca8f6857fbd0c..45c5e134d05b0d205e91d5e57ee329f695c8cb16 100644 (file)
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -2677,7 +2677,8 @@ 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_NICE))
                ret = -EACCES;
 
        if (!ret && cgroup_on_dfl(dst_cgrp)) {