audit: rebalance and remove extra layers of watch references

The audit watch count was imbalanced, adding an unnecessary layer of watch references. Only add the second reference when it is added to a parent.

Signed-off-by Richard Guy Briggs <[email protected]>

---
 kernel/audit_watch.c |    5 ++---
 kernel/auditfilter.c |   16 +++-------------
 2 files changed, 5 insertions(+), 16 deletions(-)

kernel/audit_watch.c +1 -3

index 6e30024..f33f54c 100644
@@ -203,7 +203,6 @@ int audit_to_watch(struct audit_krule *krule, char
 *path, int len, u32 op) if (IS_ERR(watch))
 		return PTR_ERR(watch);
 
-	audit_get_watch(watch);
 	krule->watch = watch;
 
 	return 0;

@@ -387,8 +386,7 @@ static void audit_add_to_parent(struct audit_krule
 *krule,
 
 		watch_found = 1;
 
-		/* put krule's and initial refs to temporary watch */
-		audit_put_watch(watch);
+		/* put krule's ref to temporary watch */
 		audit_put_watch(watch);
 

kernel/audit_watch.c +1 -0

 		audit_get_watch(w);

@@ -400,6 +398,7 @@ static void audit_add_to_parent(struct audit_krule
 *krule, audit_get_parent(parent);
 		watch->parent = parent;
 
+		audit_get_watch(watch);
 		list_add(&watch->wlist, &parent->watches);
 	}
 	list_add(&krule->rlist, &watch->rules);

kernel/auditfilter.c +3 -13

index 72e1660..4cb9b44 100644
@@ -549,8 +549,6 @@ exit_nofree:
 	return entry;
 
 exit_free:
-	if (entry->rule.watch)
-		audit_put_watch(entry->rule.watch); /* matches initial get */
 	if (entry->rule.tree)
 		audit_put_tree(entry->rule.tree); /* that's the temporary one */
 	audit_free_rule(entry);

@@ -881,7 +879,7 @@ static inline int audit_add_rule(struct audit_entry
 *entry) /* normally audit_add_tree_rule() will free it on failure */
 		if (tree)
 			audit_put_tree(tree);
-		goto error;
+		return err;
 	}
 
 	if (watch) {

@@ -895,14 +893,14 @@ static inline int audit_add_rule(struct audit_entry
 *entry) */
 			if (tree)
 				audit_put_tree(tree);
-			goto error;
+			return err;
 		}
 	}
 	if (tree) {
 		err = audit_add_tree_rule(&entry->rule);
 		if (err) {
 			mutex_unlock(&audit_filter_mutex);
-			goto error;
+			return err;
 		}
 	}
 

@@ -933,11 +931,6 @@ static inline int audit_add_rule(struct audit_entry
 *entry) #endif
 	mutex_unlock(&audit_filter_mutex);
 
- 	return 0;
-
-error:
-	if (watch)
-		audit_put_watch(watch); /* tmp watch, matches initial get */
 	return err;
 }
 

@@ -945,7 +938,6 @@ error:
 static inline int audit_del_rule(struct audit_entry *entry)
 {
 	struct audit_entry  *e;
-	struct audit_watch *watch = entry->rule.watch;
 	struct audit_tree *tree = entry->rule.tree;
 	struct list_head *list;
 	int ret = 0;

@@ -986,8 +978,6 @@ static inline int audit_del_rule(struct audit_entry
 *entry) mutex_unlock(&audit_filter_mutex);
 
 out:
-	if (watch)
-		audit_put_watch(watch); /* match initial get */
 	if (tree)
 		audit_put_tree(tree);	/* that's the temporary one */

The audit watch parent count was imbalanced, adding an unnecessary layer of watch parent references. Decrement the additional parent reference when a watch is reused, already having a reference to the parent.

audit_find_parent() gets a reference to the parent, if the parent is already known. This additional parental reference is not needed if the watch is subsequently found by audit_add_to_parent(), and consumed if the watch does not already exist, so we need to put the parent if the watch is found, and do nothing if this new watch is added to the parent.

If the parent wasn't already known, it is created with a refcount of 1 and added to the audit_watch_group, then incremented by one to be subsequently consumed by the newly created watch in audit_add_to_parent().

The rule points to the watch, not to the parent, so the rule's refcount gets bumped, not the parent's.

See LKML, 2015-07-16

Signed-off-by Richard Guy Briggs <[email protected]>

---
 kernel/audit_watch.c |    6 ++----
 1 files changed, 2 insertions(+), 4 deletions(-)

kernel/audit_watch.c +2 -1

index f33f54c..8f123d7 100644
@@ -391,11 +391,12 @@ static void audit_add_to_parent(struct audit_krule
 *krule,
 
 		audit_get_watch(w);
 		krule->watch = watch = w;
+
+		audit_put_parent(parent);
 		break;
 	}
 
 	if (!watch_found) {
-		audit_get_parent(parent);
 		watch->parent = parent;
 

kernel/audit_watch.c +0 -3

 		audit_get_watch(watch);

@@ -436,9 +437,6 @@ int audit_add_watch(struct audit_krule *krule, struct
 list_head **list)
 
 	audit_add_to_parent(krule, parent);
 
-	/* match get in audit_find_parent or audit_init_parent */
-	audit_put_parent(parent);
-
 	h = audit_hash_ino((u32)watch->ino);
 	*list = &audit_inode_hash[h];

error: