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>
[AmitP: Refactored original changes to align with upstream commit
        201af4c0fab0 ("cgroup: move cgroup files under kernel/cgroup/")]
Signed-off-by: Amit Pundir <amit.pundir@linaro.org>

diff --git a/kernel/cgroup/cgroup-v1.c b/kernel/cgroup/cgroup-v1.c
index 024085daab1aede5958235b0663c19ec667b5836..cc816dcb83c75ec1d430dd75a9e6dc0f134a05a1 100644 (file)
--- a/kernel/cgroup/cgroup-v1.c
+++ b/kernel/cgroup/cgroup-v1.c
@@ -537,7 +537,8 @@ static ssize_t __cgroup1_procs_write(struct kernfs_open_file *of,
        tcred = get_task_cred(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;
        put_cred(tcred);
        if (ret)