cred: Refcount the user_ns pointed to by the cred.

struct user_struct will shortly loose it's user_ns reference
so make the cred user_ns reference a proper reference complete
with reference counting.

Acked-by: Serge Hallyn <serge.hallyn@canonical.com>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>

2 files changed, 8 insertions, 8 deletions

diff --git a/kernel/cred.c b/kernel/cred.c
index 97b36ee..7a0d806 100644
--- a/kernel/cred.c
+++ b/kernel/cred.c
@@ -148,6 +148,7 @@ static void put_cred_rcu(struct rcu_head *rcu)
 	if (cred->group_info)
 		put_group_info(cred->group_info);
 	free_uid(cred->user);
+	put_user_ns(cred->user_ns);
 	kmem_cache_free(cred_jar, cred);
 }
 
@@ -303,6 +304,7 @@ struct cred *prepare_creds(void)
 	set_cred_subscribers(new, 0);
 	get_group_info(new->group_info);
 	get_uid(new->user);
+	get_user_ns(new->user_ns);
 
 #ifdef CONFIG_KEYS
 	key_get(new->thread_keyring);
@@ -412,11 +414,6 @@ int copy_creds(struct task_struct *p, unsigned long clone_flags)
 			goto error_put;
 	}
 
-	/* cache user_ns in cred.  Doesn't need a refcount because it will
-	 * stay pinned by cred->user
-	 */
-	new->user_ns = new->user->user_ns;
-
 #ifdef CONFIG_KEYS
 	/* new threads get their own thread keyrings if their parent already
 	 * had one */
@@ -676,6 +673,7 @@ struct cred *prepare_kernel_cred(struct task_struct *daemon)
 	atomic_set(&new->usage, 1);
 	set_cred_subscribers(new, 0);
 	get_uid(new->user);
+	get_user_ns(new->user_ns);
 	get_group_info(new->group_info);
 
 #ifdef CONFIG_KEYS
diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index f084083..58bb878 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -24,7 +24,7 @@ static struct kmem_cache *user_ns_cachep __read_mostly;
  */
 int create_user_ns(struct cred *new)
 {
-	struct user_namespace *ns;
+	struct user_namespace *ns, *parent_ns = new->user_ns;
 	struct user_struct *root_user;
 	int n;
 
@@ -57,8 +57,10 @@ int create_user_ns(struct cred *new)
 #endif
 	/* tgcred will be cleared in our caller bc CLONE_THREAD won't be set */
 
-	/* root_user holds a reference to ns, our reference can be dropped */
-	put_user_ns(ns);
+	/* Leave the reference to our user_ns with the new cred */
+	new->user_ns = ns;
+
+	put_user_ns(parent_ns);
 
 	return 0;
 }