[IPSEC]: Fix potential dst leak in xfrm_lookup

If we get an error during the actual policy lookup we don't free the
original dst while the caller expects us to always free the original
dst in case of error.

This patch fixes that.
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/xfrm/xfrm_policy.c

@@ -1318,8 +1318,9 @@ int __xfrm_lookup(struct dst_entry **dst_p, struct flowi *fl,
 
 	if (sk && sk->sk_policy[XFRM_POLICY_OUT]) {
 		policy = xfrm_sk_policy_lookup(sk, XFRM_POLICY_OUT, fl);
+		err = PTR_ERR(policy);
 		if (IS_ERR(policy))
-			return PTR_ERR(policy);
+			goto dropdst;
 	}
 
 	if (!policy) {
@@ -1330,8 +1331,9 @@ int __xfrm_lookup(struct dst_entry **dst_p, struct flowi *fl,
 
 		policy = flow_cache_lookup(fl, dst_orig->ops->family,
 					   dir, xfrm_policy_lookup);
+		err = PTR_ERR(policy);
 		if (IS_ERR(policy))
-			return PTR_ERR(policy);
+			goto dropdst;
 	}
 
 	if (!policy)
@@ -1501,8 +1503,9 @@ int __xfrm_lookup(struct dst_entry **dst_p, struct flowi *fl,
 	return 0;
 
 error:
-	dst_release(dst_orig);
 	xfrm_pols_put(pols, npols);
+dropdst:
+	dst_release(dst_orig);
 	*dst_p = NULL;
 	return err;
 }