Hey, Eric.
On Tue, Nov 06, 2012 at 07:34:07AM -0800, Eric W. Biederman wrote:
> Having thought about this a little more I can give a definitive answer.
>
> Adding a process to the device control group is equivalent to calling
> mknod, as it allows that process to open device nodes, or equivalently
> not open device nodes. Therefore a capable check is absolutely
> required.
>
> Without a capability check it would be possible to remove access to
> /dev/console for a suid root application keeping it from reporting
> attempts to hack it for example.
You understand that the whole thing is gated by VFS permission check,
right? I'm kinda lost what you're talking about.
> The generic cgroup check in attach_task_by_pid to see if you can move
> another process into a cgroup needs to be a capability call and not a
> test for uid == 0.
>
> static int attach_task_by_pid(struct cgroup *cgrp, u64 pid, bool threadgroup)
> {
> if (pid) {
> tsk = find_task_by_vpid(pid);
>
> /*
> * even if we're attaching all tasks in the thread group, we
> * only need to check permissions on one of them.
> */
> tcred = __task_cred(tsk);
> if (!uid_eq(cred->euid, GLOBAL_ROOT_UID) &&
> ^^^^^^^^^^^^^^^
> !uid_eq(cred->euid, tcred->uid) &&
> !uid_eq(cred->euid, tcred->suid)) {
> rcu_read_unlock();
> ret = -EACCES;
> goto out_unlock_cgroup;
This one isn't gated by VFS so we need to add CAP check to this
function. No?
Thanks.
--
tejun
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