netfilter: nf_tables: check for overflow of rule dlen field

commit 9889840f upstream.

Check that the space required for the expressions doesn't exceed the
size of the dlen field, which would lead to the iterators crashing.
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

net/netfilter/nf_tables_api.c

@@ -1794,6 +1794,10 @@ static int nf_tables_newrule(struct sock *nlsk, struct sk_buff *skb,
 			n++;
 		}
 	}
+	/* Check for overflow of dlen field */
+	err = -EFBIG;
+	if (size >= 1 << 12)
+		goto err1;
 
 	if (nla[NFTA_RULE_USERDATA])
 		ulen = nla_len(nla[NFTA_RULE_USERDATA]);