cgroups: fix API thinko

cgroup_attach_task_current_cg API that have upstream is backwards: we
really need an API to attach to the cgroups from another process A to
the current one.

In our case (vhost), a priveledged user wants to attach it's task to cgroups
from a less priveledged one, the API makes us run it in the other
task's context, and this fails.

So let's make the API generic and just pass in 'from' and 'to' tasks.
Add an inline wrapper for cgroup_attach_task_current_cg to avoid
breaking bisect.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Li Zefan <lizf@cn.fujitsu.com>
Acked-by: Paul Menage <menage@google.com>

1 files changed, 5 insertions, 4 deletions

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index a8ce09954404..9d90c08f3bde 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1789,10 +1789,11 @@ out:
 }
 
 /**
- * cgroup_attach_task_current_cg - attach task 'tsk' to current task's cgroup
+ * cgroup_attach_task_all - attach task 'tsk' to all cgroups of task 'from'
+ * @from: attach to all cgroups of a given task
  * @tsk: the task to be attached
  */
-int cgroup_attach_task_current_cg(struct task_struct *tsk)
+int cgroup_attach_task_all(struct task_struct *from, struct task_struct *tsk)
 {
         struct cgroupfs_root *root;
         struct cgroup *cur_cg;
@@ -1800,7 +1801,7 @@ int cgroup_attach_task_current_cg(struct task_struct *tsk)
 
         cgroup_lock();
         for_each_active_root(root) {
-                cur_cg = task_cgroup_from_root(current, root);
+                cur_cg = task_cgroup_from_root(from, root);
                 retval = cgroup_attach_task(cur_cg, tsk);
                 if (retval)
                         break;
@@ -1809,7 +1810,7 @@ int cgroup_attach_task_current_cg(struct task_struct *tsk)
 
         return retval;
 }
-EXPORT_SYMBOL_GPL(cgroup_attach_task_current_cg);
+EXPORT_SYMBOL_GPL(cgroup_attach_task_all);
 
 /*
  * Attach task with pid 'pid' to cgroup 'cgrp'. Call with cgroup_mutex