apparmor: add a conditional version of get_newest_label

get_newest_label() will always return a refcount, on the profile it
returns. However there are cases where we only need the refcount
if the label is stale and get_newest_label() will return a different
label.

Optimize this by making the get/put happen conditionally, by keeping
a flag indicating if the get was performed and a put is needed.

Signed-off-by: John Johansen <john.johansen@canonical.com>

2 files changed, 43 insertions, 11 deletions

diff --git a/security/apparmor/include/label.h b/security/apparmor/include/label.h
index 335f21930702..b5a722a47fd2 100644
--- a/security/apparmor/include/label.h
+++ b/security/apparmor/include/label.h
@@ -423,6 +423,38 @@ static inline struct aa_label *aa_get_newest_label(struct aa_label *l)
 	return aa_get_label(l);
 }
 
+/**
+ * aa_get_newest_label_condref - find the newest version of @l
+ * @l: the label to check for newer versions of
+ * @needput: returns whether the reference needs put
+ *
+ * Returns: refcounted newest version of @l taking into account
+ *          replacement, renames and removals
+ *          return @l.
+ */
+static inline struct aa_label *aa_get_newest_label_condref(struct aa_label *l,
+							   bool *needput)
+{
+	if (l && unlikely(label_is_stale(l))) {
+		struct aa_label *tmp;
+
+		AA_BUG(!l->proxy);
+		AA_BUG(!l->proxy->label);
+		/* BUG: only way this can happen is @l ref count and its
+		 * replacement count have gone to 0 and are on their way
+		 * to destruction. ie. we have a refcounting error
+		 */
+		tmp = aa_get_label_rcu(&l->proxy->label);
+		AA_BUG(!tmp);
+
+		*needput = true;
+		return tmp;
+	}
+
+	*needput = false;
+	return l;
+}
+
 static inline void aa_put_label(struct aa_label *l)
 {
 	if (l)
diff --git a/security/apparmor/label.c b/security/apparmor/label.c
index 3a721fdf1833..a8850d118c9c 100644
--- a/security/apparmor/label.c
+++ b/security/apparmor/label.c
@@ -1176,22 +1176,21 @@ static struct aa_label *__label_find_merge(struct aa_labelset *ls,
 struct aa_label *aa_label_find_merge(struct aa_label *a, struct aa_label *b)
 {
 	struct aa_labelset *ls;
-	struct aa_label *label, *ar = NULL, *br = NULL;
+	struct aa_label *label;
 	unsigned long flags;
+	bool a_needput, b_needput;
 
 	AA_BUG(!a);
 	AA_BUG(!b);
 
-	if (label_is_stale(a))
-		a = ar = aa_get_newest_label(a);
-	if (label_is_stale(b))
-		b = br = aa_get_newest_label(b);
+	a = aa_get_newest_label_condref(a, &a_needput);
+	b = aa_get_newest_label_condref(b, &b_needput);
 	ls = labelset_of_merge(a, b);
 	read_lock_irqsave(&ls->lock, flags);
 	label = __label_find_merge(ls, a, b);
 	read_unlock_irqrestore(&ls->lock, flags);
-	aa_put_label(ar);
-	aa_put_label(br);
+	aa_put_label_condref(a, a_needput);
+	aa_put_label_condref(b, b_needput);
 
 	return label;
 }
@@ -1228,9 +1227,10 @@ struct aa_label *aa_label_merge(struct aa_label *a, struct aa_label *b,
 
 	if (!label) {
 		struct aa_label *new;
+		bool a_needput, b_needput;
 
-		a = aa_get_newest_label(a);
-		b = aa_get_newest_label(b);
+		a = aa_get_newest_label_condref(a, &a_needput);
+		b = aa_get_newest_label_condref(b, &b_needput);
 
 		/* could use label_merge_len(a, b), but requires double
 		 * comparison for small savings
@@ -1242,8 +1242,8 @@ struct aa_label *aa_label_merge(struct aa_label *a, struct aa_label *b,
 		label = label_merge_insert(new, a, b);
 		label_free_or_put_new(label, new);
 out:
-		aa_put_label(a);
-		aa_put_label(b);
+		aa_put_label_condref(a, a_needput);
+		aa_put_label_condref(b, b_needput);
 	}
 
 	return label;