af_key: fix leaks in key_pol_get_resp and dump_sp.

In both functions, if pfkey_xfrm_policy2msg failed we leaked the newly
allocated sk_buff.  Free it on error.

Fixes: 55569ce2 ("Fix conversion between IPSEC_MODE_xxx and XFRM_MODE_xxx.")
Reported-by: syzbot+4f0529365f7f2208d9f0@syzkaller.appspotmail.com
Signed-off-by: Jeremy Sowden <jeremy@azazel.net>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

net/key/af_key.c

@@ -2442,8 +2442,10 @@ static int key_pol_get_resp(struct sock *sk, struct xfrm_policy *xp, const struc
 		goto out;
 	}
 	err = pfkey_xfrm_policy2msg(out_skb, xp, dir);
-	if (err < 0)
+	if (err < 0) {
+		kfree_skb(out_skb);
 		goto out;
+	}
 
 	out_hdr = (struct sadb_msg *) out_skb->data;
 	out_hdr->sadb_msg_version = hdr->sadb_msg_version;
@@ -2694,8 +2696,10 @@ static int dump_sp(struct xfrm_policy *xp, int dir, int count, void *ptr)
 		return PTR_ERR(out_skb);
 
 	err = pfkey_xfrm_policy2msg(out_skb, xp, dir);
-	if (err < 0)
+	if (err < 0) {
+		kfree_skb(out_skb);
 		return err;
+	}
 
 	out_hdr = (struct sadb_msg *) out_skb->data;
 	out_hdr->sadb_msg_version = pfk->dump.msg_version;