On Wed, Aug 31, 2016 at 01:38:35PM -0700, Andrey Vagin wrote:

On Tue, Aug 30, 2016 at 7:56 PM, Serge E. Hallyn [off-list ref] wrote:

quoted

On Fri, Aug 26, 2016 at 04:08:08PM -0700, Andrei Vagin wrote:

quoted

+struct ns_common *ns_get_owner(struct ns_common *ns)
+{
+     struct user_namespace *my_user_ns = current_user_ns();
+     struct user_namespace *owner, *p;
+
+     /* See if the owner is in the current user namespace */
+     owner = p = ns->ops->get_owner(ns);
+     for (;;) {
+             if (!p)
+                     return ERR_PTR(-EPERM);
+             if (p == my_user_ns)
+                     break;
+             p = p->parent;
+     }
+
+     return &get_user_ns(owner)->ns;

get_user_ns() bumps the owner's refcount.  I don't see where
this is being dropped, especially when ns_ioctl() uses it in
the next patch.

It is dropped in __ns_get_path if a namespace has a dentry, otherwise
it is dropped from nsfs_evict.

static void *__ns_get_path(struct path *path, struct ns_common *ns)
        |                return -EPERM;
...
        ns->ops->put(ns);                                                      |
got_it:
        |        /* See if the owner is in the current user namespace
*/
        path->mnt = mnt;
        |        owner = p = ns->ops->get_owner(ns);
        path->dentry = dentry;
        |        for (;;) {
        return NULL;
...

static void nsfs_evict(struct inode *inode)                                    |
{
        |        if (!ns_capable(user_ns, CAP_SYS_ADMIN))
        struct ns_common *ns = inode->i_private;
        |                return -EPERM;
        clear_inode(inode);                                                    |
        ns->ops->put(ns);
        |        cred = prepare_creds();
}

Gotcha, thanks.