apparmor: update how unconfined is handled

ns->unconfined is being used read side without locking, nor rcu but is
being updated when a namespace is removed. This works for the root ns
which is never removed but has a race window and can cause failures when
children namespaces are removed.

Also ns and ns->unconfined have a circular refcounting dependency that
is problematic and must be broken. Currently this is done incorrectly
when the namespace is destroyed.

Fix this by forward referencing unconfined via the replacedby infrastructure
instead of directly updating the ns->unconfined pointer.

Remove the circular refcount dependency by making the ns and its unconfined
profile share the same refcount.

Signed-off-by: John Johansen <john.johansen@canonical.com>
Acked-by: Seth Arnold <seth.arnold@canonical.com>

1 files changed, 27 insertions, 41 deletions

diff --git a/security/apparmor/policy.c b/security/apparmor/policy.c
index 41b8f27..0ceee96 100644
--- a/security/apparmor/policy.c
+++ b/security/apparmor/policy.c
@@ -141,7 +141,6 @@ static bool policy_init(struct aa_policy *policy, const char *prefix,
 	policy->name = (char *)hname_tail(policy->hname);
 	INIT_LIST_HEAD(&policy->list);
 	INIT_LIST_HEAD(&policy->profiles);
-	kref_init(&policy->count);
 
 	return 1;
 }
@@ -292,14 +291,10 @@ static struct aa_namespace *alloc_namespace(const char *prefix,
 		goto fail_unconfined;
 
 	ns->unconfined->flags = PFLAG_UNCONFINED | PFLAG_IX_ON_NAME_ERROR |
-	    PFLAG_IMMUTABLE;
+	    PFLAG_IMMUTABLE | PFLAG_NS_COUNT;
 
-	/*
-	 * released by free_namespace, however __remove_namespace breaks
-	 * the cyclic references (ns->unconfined, and unconfined->ns) and
-	 * replaces with refs to parent namespace unconfined
-	 */
-	ns->unconfined->ns = aa_get_namespace(ns);
+	/* ns and ns->unconfined share ns->unconfined refcount */
+	ns->unconfined->ns = ns;
 
 	atomic_set(&ns->uniq_null, 0);
 
@@ -312,6 +307,7 @@ fail_ns:
 	return NULL;
 }
 
+static void free_profile(struct aa_profile *profile);
 /**
  * free_namespace - free a profile namespace
  * @ns: the namespace to free  (MAYBE NULL)
@@ -327,20 +323,33 @@ static void free_namespace(struct aa_namespace *ns)
 	policy_destroy(&ns->base);
 	aa_put_namespace(ns->parent);
 
-	if (ns->unconfined && ns->unconfined->ns == ns)
-		ns->unconfined->ns = NULL;
-
-	aa_put_profile(ns->unconfined);
+	ns->unconfined->ns = NULL;
+	free_profile(ns->unconfined);
 	kzfree(ns);
 }
 
 /**
+ * aa_free_namespace_rcu - free aa_namespace by rcu
+ * @head: rcu_head callback for freeing of a profile  (NOT NULL)
+ *
+ * rcu_head is to the unconfined profile associated with the namespace
+ */
+static void aa_free_namespace_rcu(struct rcu_head *head)
+{
+	struct aa_profile *p = container_of(head, struct aa_profile, base.rcu);
+	free_namespace(p->ns);
+}
+
+/**
  * aa_free_namespace_kref - free aa_namespace by kref (see aa_put_namespace)
  * @kr: kref callback for freeing of a namespace  (NOT NULL)
+ *
+ * kref is to the unconfined profile associated with the namespace
  */
 void aa_free_namespace_kref(struct kref *kref)
 {
-	free_namespace(container_of(kref, struct aa_namespace, base.count));
+	struct aa_profile *p = container_of(kref, struct aa_profile, count);
+	call_rcu(&p->base.rcu, aa_free_namespace_rcu);
 }
 
 /**
@@ -494,8 +503,6 @@ static void __ns_list_release(struct list_head *head);
  */
 static void destroy_namespace(struct aa_namespace *ns)
 {
-	struct aa_profile *unconfined;
-
 	if (!ns)
 		return;
 
@@ -506,30 +513,11 @@ static void destroy_namespace(struct aa_namespace *ns)
 	/* release all sub namespaces */
 	__ns_list_release(&ns->sub_ns);
 
-	unconfined = ns->unconfined;
-	/*
-	 * break the ns, unconfined profile cyclic reference and forward
-	 * all new unconfined profiles requests to the parent namespace
-	 * This will result in all confined tasks that have a profile
-	 * being removed, inheriting the parent->unconfined profile.
-	 */
 	if (ns->parent)
-		ns->unconfined = aa_get_profile(ns->parent->unconfined);
-
-	/* release original ns->unconfined ref */
-	aa_put_profile(unconfined);
-
+		__aa_update_replacedby(ns->unconfined, ns->parent->unconfined);
 	mutex_unlock(&ns->lock);
 }
 
-static void aa_put_ns_rcu(struct rcu_head *head)
-{
-	struct aa_namespace *ns = container_of(head, struct aa_namespace,
-					       base.rcu);
-	/* release ns->base.list ref */
-	aa_put_namespace(ns);
-}
-
 /**
  * __remove_namespace - remove a namespace and all its children
  * @ns: namespace to be removed  (NOT NULL)
@@ -540,10 +528,8 @@ static void __remove_namespace(struct aa_namespace *ns)
 {
 	/* remove ns from namespace list */
 	list_del_rcu(&ns->base.list);
-
 	destroy_namespace(ns);
-
-	call_rcu(&ns->base.rcu, aa_put_ns_rcu);
+	aa_put_namespace(ns);
 }
 
 /**
@@ -656,8 +642,7 @@ static void aa_free_profile_rcu(struct rcu_head *head)
  */
 void aa_free_profile_kref(struct kref *kref)
 {
-	struct aa_profile *p = container_of(kref, struct aa_profile,
-					    base.count);
+	struct aa_profile *p = container_of(kref, struct aa_profile, count);
 	call_rcu(&p->base.rcu, aa_free_profile_rcu);
 }
 
@@ -683,6 +668,7 @@ struct aa_profile *aa_alloc_profile(const char *hname)
 
 	if (!policy_init(&profile->base, NULL, hname))
 		goto fail;
+	kref_init(&profile->count);
 
 	/* refcount released by caller */
 	return profile;
@@ -884,7 +870,7 @@ struct aa_profile *aa_lookup_profile(struct aa_namespace *ns, const char *hname)
 
 	/* the unconfined profile is not in the regular profile list */
 	if (!profile && strcmp(hname, "unconfined") == 0)
-		profile = aa_get_profile(ns->unconfined);
+		profile = aa_get_newest_profile(ns->unconfined);
 
 	/* refcount released by caller */
 	return profile;