cgroup: Add generic cgroup subsystem permission checks
Rather than using explicit euid == 0 checks when trying to move
tasks into a cgroup via CFS, move permission checks into each
specific cgroup subsystem. If a subsystem does not specify a
'allow_attach' handler, then we fall back to doing our checks
the old way.
Use the 'allow_attach' handler for the 'cpu' cgroup to allow
non-root processes to add arbitrary processes to a 'cpu' cgroup
if it has the CAP_SYS_NICE capability set.
This version of the patch adds a 'allow_attach' handler instead
of reusing the 'can_attach' handler. If the 'can_attach' handler
is reused, a new cgroup that implements 'can_attach' but not
the permission checks could end up with no permission checks
at all.
Change-Id: Icfa950aa9321d1ceba362061d32dc7dfa2c64f0c
Original-Author: San Mehat <san@google.com>
Signed-off-by: Colin Cross <ccross@android.com>
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index f6e7b4a..241b74a 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -2199,6 +2199,24 @@
return retval;
}
+static int cgroup_allow_attach(struct cgroup *cgrp, struct task_struct *tsk)
+{
+ struct cgroup_subsys *ss;
+ int ret;
+
+ for_each_subsys(cgrp->root, ss) {
+ if (ss->allow_attach) {
+ ret = ss->allow_attach(cgrp, tsk);
+ if (ret)
+ return ret;
+ } else {
+ return -EACCES;
+ }
+ }
+
+ return 0;
+}
+
/*
* Find the task_struct of the task to attach by vpid and pass it along to the
* function to attach either it or all tasks in its threadgroup. Will take
@@ -2244,9 +2262,16 @@
if (cred->euid &&
cred->euid != tcred->uid &&
cred->euid != tcred->suid) {
- rcu_read_unlock();
- cgroup_unlock();
- return -EACCES;
+ /*
+ * if the default permission check fails, give each
+ * cgroup a chance to extend the permission check
+ */
+ ret = cgroup_allow_attach(cgrp, tsk);
+ if (ret) {
+ rcu_read_unlock();
+ cgroup_unlock();
+ return ret;
+ }
}
get_task_struct(tsk);
rcu_read_unlock();