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, 13 insertions, 18 deletions

diff --git a/security/selinux/netif.c b/security/selinux/netif.c
index 8c738c189942..cbe6ec246412 100644
--- a/security/selinux/netif.c
+++ b/security/selinux/netif.c
@@ -135,9 +135,9 @@ static void sel_netif_destroy(struct sel_netif *netif)
  */
 static int sel_netif_sid_slow(struct net *ns, int ifindex, u32 *sid)
 {
-	int ret;
+	int ret = 0;
 	struct sel_netif *netif;
-	struct sel_netif *new = NULL;
+	struct sel_netif *new;
 	struct net_device *dev;
 
 	/* NOTE: we always use init's network namespace since we don't
@@ -154,32 +154,27 @@ static int sel_netif_sid_slow(struct net *ns, int ifindex, u32 *sid)
 	netif = sel_netif_find(ns, ifindex);
 	if (netif != NULL) {
 		*sid = netif->nsec.sid;
-		ret = 0;
 		goto out;
 	}
-	new = kzalloc(sizeof(*new), GFP_ATOMIC);
-	if (new == NULL) {
-		ret = -ENOMEM;
-		goto out;
-	}
-	ret = security_netif_sid(&selinux_state, dev->name, &new->nsec.sid);
-	if (ret != 0)
-		goto out;
-	new->nsec.ns = ns;
-	new->nsec.ifindex = ifindex;
-	ret = sel_netif_insert(new);
+
+	ret = security_netif_sid(&selinux_state, dev->name, sid);
 	if (ret != 0)
 		goto out;
-	*sid = new->nsec.sid;
+	new = kzalloc(sizeof(*new), GFP_ATOMIC);
+	if (new) {
+		new->nsec.ns = ns;
+		new->nsec.ifindex = ifindex;
+		new->nsec.sid = *sid;
+		if (sel_netif_insert(new))
+			kfree(new);
+	}
 
 out:
 	spin_unlock_bh(&sel_netif_lock);
 	dev_put(dev);
-	if (unlikely(ret)) {
+	if (unlikely(ret))
 		pr_warn("SELinux: failure in %s(), unable to determine network interface label (%d)\n",
 			__func__, ifindex);
-		kfree(new);
-	}
 	return ret;
 }