selinux: always return a secid from the network caches if we find one

Previously if we couldn't find an entry in the cache and we failed to
allocate memory for a new cache entry we would fail the network object
label lookup; this is obviously not ideal.  This patch fixes this so
that we return the object label even if we can't cache the object at
this point in time due to memory pressure.

The GitHub issue tracker is below:
 * https://github.com/SELinuxProject/selinux-kernel/issues/3

Signed-off-by: Paul Moore <paul@paul-moore.com>

1 files changed, 14 insertions, 16 deletions

diff --git a/security/selinux/netnode.c b/security/selinux/netnode.c
index afa0d432436b..df590aaa33f4 100644
--- a/security/selinux/netnode.c
+++ b/security/selinux/netnode.c
@@ -199,9 +199,9 @@ static void sel_netnode_insert(struct sel_netnode *node)
  */
 static int sel_netnode_sid_slow(void *addr, u16 family, u32 *sid)
 {
-	int ret = -ENOMEM;
+	int ret;
 	struct sel_netnode *node;
-	struct sel_netnode *new = NULL;
+	struct sel_netnode *new;
 
 	spin_lock_bh(&sel_netnode_lock);
 	node = sel_netnode_find(addr, family);
@@ -210,38 +210,36 @@ static int sel_netnode_sid_slow(void *addr, u16 family, u32 *sid)
 		spin_unlock_bh(&sel_netnode_lock);
 		return 0;
 	}
+
 	new = kzalloc(sizeof(*new), GFP_ATOMIC);
-	if (new == NULL)
-		goto out;
 	switch (family) {
 	case PF_INET:
 		ret = security_node_sid(&selinux_state, PF_INET,
 					addr, sizeof(struct in_addr), sid);
-		new->nsec.addr.ipv4 = *(__be32 *)addr;
+		if (new)
+			new->nsec.addr.ipv4 = *(__be32 *)addr;
 		break;
 	case PF_INET6:
 		ret = security_node_sid(&selinux_state, PF_INET6,
 					addr, sizeof(struct in6_addr), sid);
-		new->nsec.addr.ipv6 = *(struct in6_addr *)addr;
+		if (new)
+			new->nsec.addr.ipv6 = *(struct in6_addr *)addr;
 		break;
 	default:
 		BUG();
 		ret = -EINVAL;
 	}
-	if (ret != 0)
-		goto out;
-
-	new->nsec.family = family;
-	new->nsec.sid = *sid;
-	sel_netnode_insert(new);
+	if (ret == 0 && new) {
+		new->nsec.family = family;
+		new->nsec.sid = *sid;
+		sel_netnode_insert(new);
+	} else
+		kfree(new);
 
-out:
 	spin_unlock_bh(&sel_netnode_lock);
-	if (unlikely(ret)) {
+	if (unlikely(ret))
 		pr_warn("SELinux: failure in %s(), unable to determine network node label\n",
 			__func__);
-		kfree(new);
-	}
 	return ret;
 }