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, 39 insertions, 41 deletions

diff --git a/security/apparmor/include/policy.h b/security/apparmor/include/policy.h
index e9f2baf4467..1ddd5e5728b 100644
--- a/security/apparmor/include/policy.h
+++ b/security/apparmor/include/policy.h
@@ -68,6 +68,7 @@ enum profile_flags {
 	PFLAG_NO_LIST_REF = 0x40,	/* list doesn't keep profile ref */
 	PFLAG_OLD_NULL_TRANS = 0x100,	/* use // as the null transition */
 	PFLAG_INVALID = 0x200,		/* profile replaced/removed */
+	PFLAG_NS_COUNT = 0x400,		/* carries NS ref count */
 
 	/* These flags must correspond with PATH_flags */
 	PFLAG_MEDIATE_DELETED = 0x10000, /* mediate instead delegate deleted */
@@ -78,7 +79,6 @@ struct aa_profile;
 /* struct aa_policy - common part of both namespaces and profiles
  * @name: name of the object
  * @hname - The hierarchical name
- * @count: reference count of the obj
  * @list: list policy object is on
  * @rcu: rcu head used when removing from @list
  * @profiles: head of the profiles list contained in the object
@@ -86,7 +86,6 @@ struct aa_profile;
 struct aa_policy {
 	char *name;
 	char *hname;
-	struct kref count;
 	struct list_head list;
 	struct list_head profiles;
 	struct rcu_head rcu;
@@ -157,6 +156,7 @@ struct aa_replacedby {
 
 /* struct aa_profile - basic confinement data
  * @base - base components of the profile (name, refcount, lists, lock ...)
+ * @count: reference count of the obj
  * @parent: parent of profile
  * @ns: namespace the profile is in
  * @replacedby: is set to the profile that replaced this profile
@@ -189,6 +189,7 @@ struct aa_replacedby {
  */
 struct aa_profile {
 	struct aa_policy base;
+	struct kref count;
 	struct aa_profile __rcu *parent;
 
 	struct aa_namespace *ns;
@@ -223,40 +224,6 @@ void aa_free_namespace_kref(struct kref *kref);
 struct aa_namespace *aa_find_namespace(struct aa_namespace *root,
 				       const char *name);
 
-static inline struct aa_policy *aa_get_common(struct aa_policy *c)
-{
-	if (c)
-		kref_get(&c->count);
-
-	return c;
-}
-
-/**
- * aa_get_namespace - increment references count on @ns
- * @ns: namespace to increment reference count of (MAYBE NULL)
- *
- * Returns: pointer to @ns, if @ns is NULL returns NULL
- * Requires: @ns must be held with valid refcount when called
- */
-static inline struct aa_namespace *aa_get_namespace(struct aa_namespace *ns)
-{
-	if (ns)
-		kref_get(&(ns->base.count));
-
-	return ns;
-}
-
-/**
- * aa_put_namespace - decrement refcount on @ns
- * @ns: namespace to put reference of
- *
- * Decrement reference count of @ns and if no longer in use free it
- */
-static inline void aa_put_namespace(struct aa_namespace *ns)
-{
-	if (ns)
-		kref_put(&ns->base.count, aa_free_namespace_kref);
-}
 
 void aa_free_replacedby_kref(struct kref *kref);
 struct aa_profile *aa_alloc_profile(const char *name);
@@ -285,7 +252,7 @@ ssize_t aa_remove_profiles(char *name, size_t size);
 static inline struct aa_profile *aa_get_profile(struct aa_profile *p)
 {
 	if (p)
-		kref_get(&(p->base.count));
+		kref_get(&(p->count));
 
 	return p;
 }
@@ -299,7 +266,7 @@ static inline struct aa_profile *aa_get_profile(struct aa_profile *p)
  */
 static inline struct aa_profile *aa_get_profile_not0(struct aa_profile *p)
 {
-	if (p && kref_get_not0(&p->base.count))
+	if (p && kref_get_not0(&p->count))
 		return p;
 
 	return NULL;
@@ -319,7 +286,7 @@ static inline struct aa_profile *aa_get_profile_rcu(struct aa_profile __rcu **p)
 	rcu_read_lock();
 	do {
 		c = rcu_dereference(*p);
-	} while (c && !kref_get_not0(&c->base.count));
+	} while (c && !kref_get_not0(&c->count));
 	rcu_read_unlock();
 
 	return c;
@@ -350,8 +317,12 @@ static inline struct aa_profile *aa_get_newest_profile(struct aa_profile *p)
  */
 static inline void aa_put_profile(struct aa_profile *p)
 {
-	if (p)
-		kref_put(&p->base.count, aa_free_profile_kref);
+	if (p) {
+		if (p->flags & PFLAG_NS_COUNT)
+			kref_put(&p->count, aa_free_namespace_kref);
+		else
+			kref_put(&p->count, aa_free_profile_kref);
+	}
 }
 
 static inline struct aa_replacedby *aa_get_replacedby(struct aa_replacedby *p)
@@ -378,6 +349,33 @@ static inline void __aa_update_replacedby(struct aa_profile *orig,
 	aa_put_profile(tmp);
 }
 
+/**
+ * aa_get_namespace - increment references count on @ns
+ * @ns: namespace to increment reference count of (MAYBE NULL)
+ *
+ * Returns: pointer to @ns, if @ns is NULL returns NULL
+ * Requires: @ns must be held with valid refcount when called
+ */
+static inline struct aa_namespace *aa_get_namespace(struct aa_namespace *ns)
+{
+	if (ns)
+		aa_get_profile(ns->unconfined);
+
+	return ns;
+}
+
+/**
+ * aa_put_namespace - decrement refcount on @ns
+ * @ns: namespace to put reference of
+ *
+ * Decrement reference count of @ns and if no longer in use free it
+ */
+static inline void aa_put_namespace(struct aa_namespace *ns)
+{
+	if (ns)
+		aa_put_profile(ns->unconfined);
+}
+
 static inline int AUDIT_MODE(struct aa_profile *profile)
 {
 	if (aa_g_audit != AUDIT_NORMAL)