Smack: Rule list lookup performance

This patch is targeted for the smack-next tree.

Smack access checks suffer from two significant performance
issues. In cases where there are large numbers of rules the
search of the single list of rules is wasteful. Comparing the
string values of the smack labels is less efficient than a
numeric comparison would.

These changes take advantage of the Smack label list, which
maintains the mapping of Smack labels to secids and optional
CIPSO labels. Because the labels are kept perpetually, an
access check can be done strictly based on the address of the
label in the list without ever looking at the label itself.
Rather than keeping one global list of rules the rules with
a particular subject label can be based off of that label
list entry. The access check need never look at entries that
do not use the current subject label.

This requires that packets coming off the network with
CIPSO direct Smack labels that have never been seen before
be treated carefully. The only case where they could be
delivered is where the receiving socket has an IPIN star
label, so that case is explicitly addressed.

On a system with 39,800 rules (200 labels in all permutations)
a system with this patch runs an access speed test in 5% of
the time of the old version. That should be a best case
improvement. If all of the rules are associated with the
same subject label and all of the accesses are for processes
with that label (unlikely) the improvement is about 30%.

Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>

1 files changed, 56 insertions, 57 deletions

diff --git a/security/smack/smack_access.c b/security/smack/smack_access.c
index 9637e107f7ea..a885f628f56e 100644
--- a/security/smack/smack_access.c
+++ b/security/smack/smack_access.c
@@ -77,14 +77,19 @@ int log_policy = SMACK_AUDIT_DENIED;
  * entry is found returns -ENOENT.
  *
  * NOTE:
- * Even though Smack labels are usually shared on smack_list
- * labels that come in off the network can't be imported
- * and added to the list for locking reasons.
  *
- * Therefore, it is necessary to check the contents of the labels,
- * not just the pointer values. Of course, in most cases the labels
- * will be on the list, so checking the pointers may be a worthwhile
- * optimization.
+ * Earlier versions of this function allowed for labels that
+ * were not on the label list. This was done to allow for
+ * labels to come over the network that had never been seen
+ * before on this host. Unless the receiving socket has the
+ * star label this will always result in a failure check. The
+ * star labeled socket case is now handled in the networking
+ * hooks so there is no case where the label is not on the
+ * label list. Checking to see if the address of two labels
+ * is the same is now a reliable test.
+ *
+ * Do the object check first because that is more
+ * likely to differ.
  */
 int smk_access_entry(char *subject_label, char *object_label,
 			struct list_head *rule_list)
@@ -93,13 +98,10 @@ int smk_access_entry(char *subject_label, char *object_label,
 	struct smack_rule *srp;
 
 	list_for_each_entry_rcu(srp, rule_list, list) {
-		if (srp->smk_subject == subject_label ||
-		    strcmp(srp->smk_subject, subject_label) == 0) {
-			if (srp->smk_object == object_label ||
-			    strcmp(srp->smk_object, object_label) == 0) {
-				may = srp->smk_access;
-				break;
-			}
+		if (srp->smk_object == object_label &&
+		    srp->smk_subject == subject_label) {
+			may = srp->smk_access;
+			break;
 		}
 	}
 
@@ -117,18 +119,12 @@ int smk_access_entry(char *subject_label, char *object_label,
  * access rule list and returns 0 if the access is permitted,
  * non zero otherwise.
  *
- * Even though Smack labels are usually shared on smack_list
- * labels that come in off the network can't be imported
- * and added to the list for locking reasons.
- *
- * Therefore, it is necessary to check the contents of the labels,
- * not just the pointer values. Of course, in most cases the labels
- * will be on the list, so checking the pointers may be a worthwhile
- * optimization.
+ * Smack labels are shared on smack_list
  */
 int smk_access(char *subject_label, char *object_label, int request,
 	       struct smk_audit_info *a)
 {
+	struct smack_known *skp;
 	int may = MAY_NOT;
 	int rc = 0;
 
@@ -137,8 +133,7 @@ int smk_access(char *subject_label, char *object_label, int request,
 	 *
 	 * A star subject can't access any object.
 	 */
-	if (subject_label == smack_known_star.smk_known ||
-	    strcmp(subject_label, smack_known_star.smk_known) == 0) {
+	if (subject_label == smack_known_star.smk_known) {
 		rc = -EACCES;
 		goto out_audit;
 	}
@@ -148,33 +143,27 @@ int smk_access(char *subject_label, char *object_label, int request,
 	 * An internet subject can access any object.
 	 */
 	if (object_label == smack_known_web.smk_known ||
-	    subject_label == smack_known_web.smk_known ||
-	    strcmp(object_label, smack_known_web.smk_known) == 0 ||
-	    strcmp(subject_label, smack_known_web.smk_known) == 0)
+	    subject_label == smack_known_web.smk_known)
 		goto out_audit;
 	/*
 	 * A star object can be accessed by any subject.
 	 */
-	if (object_label == smack_known_star.smk_known ||
-	    strcmp(object_label, smack_known_star.smk_known) == 0)
+	if (object_label == smack_known_star.smk_known)
 		goto out_audit;
 	/*
 	 * An object can be accessed in any way by a subject
 	 * with the same label.
 	 */
-	if (subject_label == object_label ||
-	    strcmp(subject_label, object_label) == 0)
+	if (subject_label == object_label)
 		goto out_audit;
 	/*
 	 * A hat subject can read any object.
 	 * A floor object can be read by any subject.
 	 */
 	if ((request & MAY_ANYREAD) == request) {
-		if (object_label == smack_known_floor.smk_known ||
-		    strcmp(object_label, smack_known_floor.smk_known) == 0)
+		if (object_label == smack_known_floor.smk_known)
 			goto out_audit;
-		if (subject_label == smack_known_hat.smk_known ||
-		    strcmp(subject_label, smack_known_hat.smk_known) == 0)
+		if (subject_label == smack_known_hat.smk_known)
 			goto out_audit;
 	}
 	/*
@@ -184,8 +173,9 @@ int smk_access(char *subject_label, char *object_label, int request,
 	 * good. A negative response from smk_access_entry()
 	 * indicates there is no entry for this pair.
 	 */
+	skp = smk_find_entry(subject_label);
 	rcu_read_lock();
-	may = smk_access_entry(subject_label, object_label, &smack_rule_list);
+	may = smk_access_entry(subject_label, object_label, &skp->smk_rules);
 	rcu_read_unlock();
 
 	if (may > 0 && (request & may) == request)
@@ -344,6 +334,25 @@ void smack_log(char *subject_label, char *object_label, int request,
 static DEFINE_MUTEX(smack_known_lock);
 
 /**
+ * smk_find_entry - find a label on the list, return the list entry
+ * @string: a text string that might be a Smack label
+ *
+ * Returns a pointer to the entry in the label list that
+ * matches the passed string.
+ */
+struct smack_known *smk_find_entry(const char *string)
+{
+	struct smack_known *skp;
+
+	list_for_each_entry_rcu(skp, &smack_known_list, list) {
+		if (strncmp(skp->smk_known, string, SMK_MAXLEN) == 0)
+			return skp;
+	}
+
+	return NULL;
+}
+
+/**
  * smk_import_entry - import a label, return the list entry
  * @string: a text string that might be a Smack label
  * @len: the maximum size, or zero if it is NULL terminated.
@@ -378,21 +387,17 @@ struct smack_known *smk_import_entry(const char *string, int len)
 
 	mutex_lock(&smack_known_lock);
 
-	found = 0;
-	list_for_each_entry_rcu(skp, &smack_known_list, list) {
-		if (strncmp(skp->smk_known, smack, SMK_MAXLEN) == 0) {
-			found = 1;
-			break;
-		}
-	}
+	skp = smk_find_entry(smack);
 
-	if (found == 0) {
+	if (skp == NULL) {
 		skp = kzalloc(sizeof(struct smack_known), GFP_KERNEL);
 		if (skp != NULL) {
 			strncpy(skp->smk_known, smack, SMK_MAXLEN);
 			skp->smk_secid = smack_next_secid++;
 			skp->smk_cipso = NULL;
+			INIT_LIST_HEAD(&skp->smk_rules);
 			spin_lock_init(&skp->smk_cipsolock);
+			mutex_init(&skp->smk_rules_lock);
 			/*
 			 * Make sure that the entry is actually
 			 * filled before putting it on the list.
@@ -480,19 +485,12 @@ u32 smack_to_secid(const char *smack)
  * smack_from_cipso - find the Smack label associated with a CIPSO option
  * @level: Bell & LaPadula level from the network
  * @cp: Bell & LaPadula categories from the network
- * @result: where to put the Smack value
  *
  * This is a simple lookup in the label table.
  *
- * This is an odd duck as far as smack handling goes in that
- * it sends back a copy of the smack label rather than a pointer
- * to the master list. This is done because it is possible for
- * a foreign host to send a smack label that is new to this
- * machine and hence not on the list. That would not be an
- * issue except that adding an entry to the master list can't
- * be done at that point.
+ * Return the matching label from the label list or NULL.
  */
-void smack_from_cipso(u32 level, char *cp, char *result)
+char *smack_from_cipso(u32 level, char *cp)
 {
 	struct smack_known *kp;
 	char *final = NULL;
@@ -509,12 +507,13 @@ void smack_from_cipso(u32 level, char *cp, char *result)
 			final = kp->smk_known;
 
 		spin_unlock_bh(&kp->smk_cipsolock);
+
+		if (final != NULL)
+			break;
 	}
 	rcu_read_unlock();
-	if (final == NULL)
-		final = smack_known_huh.smk_known;
-	strncpy(result, final, SMK_MAXLEN);
-	return;
+
+	return final;
 }
 
 /**