netfilter: synproxy: Check oom when adding synproxy and seqadj ct extensions

When memory is exhausted, nfct_seqadj_ext_add may fail to add the
synproxy and seqadj extensions. The function nf_ct_seqadj_init doesn't
check if get valid seqadj pointer by the nfct_seqadj.

Now drop the packet directly when fail to add seqadj extension to
avoid dereference NULL pointer in nf_ct_seqadj_init from
init_conntrack().
Signed-off-by: Gao Feng <fgao@ikuai8.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

include/net/netfilter/nf_conntrack_synproxy.h

@@ -27,6 +27,20 @@ static inline struct nf_conn_synproxy *nfct_synproxy_ext_add(struct nf_conn *ct)
 #endif
 }
 
+static inline bool nf_ct_add_synproxy(struct nf_conn *ct,
+				      const struct nf_conn *tmpl)
+{
+	if (tmpl && nfct_synproxy(tmpl)) {
+		if (!nfct_seqadj_ext_add(ct))
+			return false;
+
+		if (!nfct_synproxy_ext_add(ct))
+			return false;
+	}
+
+	return true;
+}
+
 struct synproxy_stats {
 	unsigned int			syn_received;
 	unsigned int			cookie_invalid;

net/netfilter/nf_conntrack_core.c

@@ -1035,9 +1035,9 @@ init_conntrack(struct net *net, struct nf_conn *tmpl,
 	if (IS_ERR(ct))
 		return (struct nf_conntrack_tuple_hash *)ct;
 
-	if (tmpl && nfct_synproxy(tmpl)) {
-		nfct_seqadj_ext_add(ct);
-		nfct_synproxy_ext_add(ct);
+	if (!nf_ct_add_synproxy(ct, tmpl)) {
+		nf_conntrack_free(ct);
+		return ERR_PTR(-ENOMEM);
 	}
 
 	timeout_ext = tmpl ? nf_ct_timeout_find(tmpl) : NULL;

net/netfilter/nf_nat_core.c

@@ -441,7 +441,8 @@ nf_nat_setup_info(struct nf_conn *ct,
 			ct->status |= IPS_DST_NAT;
 
 		if (nfct_help(ct))
-			nfct_seqadj_ext_add(ct);
+			if (!nfct_seqadj_ext_add(ct))
+				return NF_DROP;
 	}
 
 	if (maniptype == NF_NAT_MANIP_SRC) {