Hi Paul,
Attaching PID 0 to a cgroup caused the current task to be attached to
the cgroup. Looking at the code,
if (pid) {
rcu_read_lock();
tsk = find_task_by_vpid(pid);
if (!tsk || tsk->flags & PF_EXITING) {
rcu_read_unlock();
return -ESRCH;
}
get_task_struct(tsk);
rcu_read_unlock();
if ((current->euid) && (current->euid != tsk->uid)
&& (current->euid != tsk->suid)) {
put_task_struct(tsk);
return -EACCES;
}
} else {
tsk = current;
get_task_struct(tsk);
}
I was wondering, why this was done. It seems to be unexpected behavior.
Wouldn't something like the following be a better response? (I've used
EINVAL, but I can change it to ESRCH if that is better.)
---
cgroups: Don't allow PID 0 to be attached to a group
Currently when one trys to attach PID 0 to a cgroup, it attaches
the current task. That is not expected behavior. It should return
an error instead.
Signed-off-by: Dhaval Giani <dhaval@linux.vnet.ibm.com>
Index: linux-2.6/kernel/cgroup.c
===================================================================
--- linux-2.6.orig/kernel/cgroup.c
+++ linux-2.6/kernel/cgroup.c
@@ -1309,8 +1309,7 @@ static int attach_task_by_pid(struct cgr
return -EACCES;
}
} else {
- tsk = current;
- get_task_struct(tsk);
+ return -EINVAL;
}
ret = cgroup_attach_task(cgrp, tsk);
--
regards,
Dhaval
--
