selinux: refactor avtab_node comparisons

In four separate functions within avtab, the same comparison logic is
used. The only difference is how the result is handled or whether there
is a unique specifier value to be checked for or used.

Extracting this functionality into the avtab_node_cmp() function unifies
the comparison logic between searching and insertion and gets rid of
duplicative code so that the implementation is easier to maintain.
Signed-off-by: Jacob Satterfield <jsatterfield.linux@gmail.com>
Reviewed-by: Stephen Smalley <stephen.smalley.work@gmail.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>

security/selinux/ss/avtab.c

@@ -96,12 +96,34 @@ avtab_insert_node(struct avtab *h, struct avtab_node **dst,
 	return newnode;
 }
 
+static int avtab_node_cmp(const struct avtab_key *key1,
+			  const struct avtab_key *key2)
+{
+	u16 specified = key1->specified & ~(AVTAB_ENABLED|AVTAB_ENABLED_OLD);
+
+	if (key1->source_type == key2->source_type &&
+	    key1->target_type == key2->target_type &&
+	    key1->target_class == key2->target_class &&
+	    (specified & key2->specified))
+		return 0;
+	if (key1->source_type < key2->source_type)
+		return -1;
+	if (key1->source_type == key2->source_type &&
+	    key1->target_type < key2->target_type)
+		return -1;
+	if (key1->source_type == key2->source_type &&
+	    key1->target_type == key2->target_type &&
+	    key1->target_class < key2->target_class)
+		return -1;
+	return 1;
+}
+
 static int avtab_insert(struct avtab *h, const struct avtab_key *key,
 			const struct avtab_datum *datum)
 {
 	u32 hvalue;
 	struct avtab_node *prev, *cur, *newnode;
-	u16 specified = key->specified & ~(AVTAB_ENABLED|AVTAB_ENABLED_OLD);
+	int cmp;
 
 	if (!h || !h->nslot || h->nel == U32_MAX)
 		return -EINVAL;
@@ -110,23 +132,11 @@ static int avtab_insert(struct avtab *h, const struct avtab_key *key,
 	for (prev = NULL, cur = h->htable[hvalue];
 	     cur;
 	     prev = cur, cur = cur->next) {
-		if (key->source_type == cur->key.source_type &&
-		    key->target_type == cur->key.target_type &&
-		    key->target_class == cur->key.target_class &&
-		    (specified & cur->key.specified)) {
-			/* extended perms may not be unique */
-			if (specified & AVTAB_XPERMS)
-				break;
+		cmp = avtab_node_cmp(key, &cur->key);
+		/* extended perms may not be unique */
+		if (cmp == 0 && !(key->specified & AVTAB_XPERMS))
 			return -EEXIST;
-		}
-		if (key->source_type < cur->key.source_type)
-			break;
-		if (key->source_type == cur->key.source_type &&
-		    key->target_type < cur->key.target_type)
-			break;
-		if (key->source_type == cur->key.source_type &&
-		    key->target_type == cur->key.target_type &&
-		    key->target_class < cur->key.target_class)
+		if (cmp <= 0)
 			break;
 	}
 
@@ -148,7 +158,7 @@ struct avtab_node *avtab_insert_nonunique(struct avtab *h,
 {
 	u32 hvalue;
 	struct avtab_node *prev, *cur;
-	u16 specified = key->specified & ~(AVTAB_ENABLED|AVTAB_ENABLED_OLD);
+	int cmp;
 
 	if (!h || !h->nslot || h->nel == U32_MAX)
 		return NULL;
@@ -156,19 +166,8 @@ struct avtab_node *avtab_insert_nonunique(struct avtab *h,
 	for (prev = NULL, cur = h->htable[hvalue];
 	     cur;
 	     prev = cur, cur = cur->next) {
-		if (key->source_type == cur->key.source_type &&
-		    key->target_type == cur->key.target_type &&
-		    key->target_class == cur->key.target_class &&
-		    (specified & cur->key.specified))
-			break;
-		if (key->source_type < cur->key.source_type)
-			break;
-		if (key->source_type == cur->key.source_type &&
-		    key->target_type < cur->key.target_type)
-			break;
-		if (key->source_type == cur->key.source_type &&
-		    key->target_type == cur->key.target_type &&
-		    key->target_class < cur->key.target_class)
+		cmp = avtab_node_cmp(key, &cur->key);
+		if (cmp <= 0)
 			break;
 	}
 	return avtab_insert_node(h, prev ? &prev->next : &h->htable[hvalue],
@@ -183,7 +182,7 @@ struct avtab_node *avtab_search_node(struct avtab *h,
 {
 	u32 hvalue;
 	struct avtab_node *cur;
-	u16 specified = key->specified & ~(AVTAB_ENABLED|AVTAB_ENABLED_OLD);
+	int cmp;
 
 	if (!h || !h->nslot)
 		return NULL;
@@ -191,20 +190,10 @@ struct avtab_node *avtab_search_node(struct avtab *h,
 	hvalue = avtab_hash(key, h->mask);
 	for (cur = h->htable[hvalue]; cur;
 	     cur = cur->next) {
-		if (key->source_type == cur->key.source_type &&
-		    key->target_type == cur->key.target_type &&
-		    key->target_class == cur->key.target_class &&
-		    (specified & cur->key.specified))
+		cmp = avtab_node_cmp(key, &cur->key);
+		if (cmp == 0)
 			return cur;
-
-		if (key->source_type < cur->key.source_type)
-			break;
-		if (key->source_type == cur->key.source_type &&
-		    key->target_type < cur->key.target_type)
-			break;
-		if (key->source_type == cur->key.source_type &&
-		    key->target_type == cur->key.target_type &&
-		    key->target_class < cur->key.target_class)
+		if (cmp < 0)
 			break;
 	}
 	return NULL;
@@ -213,27 +202,19 @@ struct avtab_node *avtab_search_node(struct avtab *h,
 struct avtab_node*
 avtab_search_node_next(struct avtab_node *node, u16 specified)
 {
+	struct avtab_key tmp_key;
 	struct avtab_node *cur;
+	int cmp;
 
 	if (!node)
 		return NULL;
-
-	specified &= ~(AVTAB_ENABLED|AVTAB_ENABLED_OLD);
+	tmp_key = node->key;
+	tmp_key.specified = specified;
 	for (cur = node->next; cur; cur = cur->next) {
-		if (node->key.source_type == cur->key.source_type &&
-		    node->key.target_type == cur->key.target_type &&
-		    node->key.target_class == cur->key.target_class &&
-		    (specified & cur->key.specified))
+		cmp = avtab_node_cmp(&tmp_key, &cur->key);
+		if (cmp == 0)
 			return cur;
-
-		if (node->key.source_type < cur->key.source_type)
-			break;
-		if (node->key.source_type == cur->key.source_type &&
-		    node->key.target_type < cur->key.target_type)
-			break;
-		if (node->key.source_type == cur->key.source_type &&
-		    node->key.target_type == cur->key.target_type &&
-		    node->key.target_class < cur->key.target_class)
+		if (cmp < 0)
 			break;
 	}
 	return NULL;