netfilter: introduce nft_set_pktinfo_{ipv4, ipv6}_validate()

These functions are extracted from the netdev family, they initialize
the pktinfo structure and validate that the IPv4 and IPv6 headers are
well-formed given that these functions are called from a path where
layer 3 sanitization did not happen yet.

These functions are placed in include/net/netfilter/nf_tables_ipv{4,6}.h
so they can be reused by a follow up patch to use them from the bridge
family too.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

2 files changed, 91 insertions, 0 deletions

diff --git a/include/net/netfilter/nf_tables_ipv4.h b/include/net/netfilter/nf_tables_ipv4.h
index af952f7843ee..968f00b82fb5 100644
--- a/include/net/netfilter/nf_tables_ipv4.h
+++ b/include/net/netfilter/nf_tables_ipv4.h
@@ -20,6 +20,48 @@ nft_set_pktinfo_ipv4(struct nft_pktinfo *pkt,
 	pkt->xt.fragoff = ntohs(ip->frag_off) & IP_OFFSET;
 }
 
+static inline int
+__nft_set_pktinfo_ipv4_validate(struct nft_pktinfo *pkt,
+				struct sk_buff *skb,
+				const struct nf_hook_state *state)
+{
+	struct iphdr *iph, _iph;
+	u32 len, thoff;
+
+	iph = skb_header_pointer(skb, skb_network_offset(skb), sizeof(*iph),
+				 &_iph);
+	if (!iph)
+		return -1;
+
+	iph = ip_hdr(skb);
+	if (iph->ihl < 5 || iph->version != 4)
+		return -1;
+
+	len = ntohs(iph->tot_len);
+	thoff = iph->ihl * 4;
+	if (skb->len < len)
+		return -1;
+	else if (len < thoff)
+		return -1;
+
+	pkt->tprot_set = true;
+	pkt->tprot = iph->protocol;
+	pkt->xt.thoff = thoff;
+	pkt->xt.fragoff = ntohs(iph->frag_off) & IP_OFFSET;
+
+	return 0;
+}
+
+static inline void
+nft_set_pktinfo_ipv4_validate(struct nft_pktinfo *pkt,
+			      struct sk_buff *skb,
+			      const struct nf_hook_state *state)
+{
+	nft_set_pktinfo(pkt, skb, state);
+	if (__nft_set_pktinfo_ipv4_validate(pkt, skb, state) < 0)
+		nft_set_pktinfo_proto_unspec(pkt, skb);
+}
+
 extern struct nft_af_info nft_af_ipv4;
 
 #endif
diff --git a/include/net/netfilter/nf_tables_ipv6.h b/include/net/netfilter/nf_tables_ipv6.h
index 1e0ffd5aea47..39b7b717b540 100644
--- a/include/net/netfilter/nf_tables_ipv6.h
+++ b/include/net/netfilter/nf_tables_ipv6.h
@@ -28,6 +28,55 @@ nft_set_pktinfo_ipv6(struct nft_pktinfo *pkt,
 	return 0;
 }
 
+static inline int
+__nft_set_pktinfo_ipv6_validate(struct nft_pktinfo *pkt,
+				struct sk_buff *skb,
+				const struct nf_hook_state *state)
+{
+#if IS_ENABLED(CONFIG_IPV6)
+	struct ipv6hdr *ip6h, _ip6h;
+	unsigned int thoff = 0;
+	unsigned short frag_off;
+	int protohdr;
+	u32 pkt_len;
+
+	ip6h = skb_header_pointer(skb, skb_network_offset(skb), sizeof(*ip6h),
+				  &_ip6h);
+	if (!ip6h)
+		return -1;
+
+	if (ip6h->version != 6)
+		return -1;
+
+	pkt_len = ntohs(ip6h->payload_len);
+	if (pkt_len + sizeof(*ip6h) > skb->len)
+		return -1;
+
+	protohdr = ipv6_find_hdr(pkt->skb, &thoff, -1, &frag_off, NULL);
+	if (protohdr < 0)
+		return -1;
+
+	pkt->tprot_set = true;
+	pkt->tprot = protohdr;
+	pkt->xt.thoff = thoff;
+	pkt->xt.fragoff = frag_off;
+
+	return 0;
+#else
+	return -1;
+#endif
+}
+
+static inline void
+nft_set_pktinfo_ipv6_validate(struct nft_pktinfo *pkt,
+			      struct sk_buff *skb,
+			      const struct nf_hook_state *state)
+{
+	nft_set_pktinfo(pkt, skb, state);
+	if (__nft_set_pktinfo_ipv6_validate(pkt, skb, state) < 0)
+		nft_set_pktinfo_proto_unspec(pkt, skb);
+}
+
 extern struct nft_af_info nft_af_ipv6;
 
 #endif