netfilter: nf_reject: add reject skbuff creation helpers

Adds reject skbuff creation helper functions to ipv4/6 nf_reject
infrastructure. Use these functions for reject verdict in bridge
family.

Can be reused by all different families that support reject and
will not inject the reject packet through ip local out.

Signed-off-by: Jose M. Guisado Gomez <[e-mail]>
Signed-off-by: Pablo Neira Ayuso <[e-mail]>

include/net/netfilter/ipv4/nf_reject.h

···
 void nf_reject_ip_tcphdr_put(struct sk_buff *nskb, const struct sk_buff *oldskb,
 			     const struct tcphdr *oth);
 
+struct sk_buff *nf_reject_skb_v4_unreach(struct net *net,
+                                         struct sk_buff *oldskb,
+                                         const struct net_device *dev,
+                                         int hook, u8 code);
+struct sk_buff *nf_reject_skb_v4_tcp_reset(struct net *net,
+					   struct sk_buff *oldskb,
+					   const struct net_device *dev,
+					   int hook);
+
+
 #endif /* _IPV4_NF_REJECT_H */

include/net/netfilter/ipv6/nf_reject.h

···
 			      const struct sk_buff *oldskb,
 			      const struct tcphdr *oth, unsigned int otcplen);
 
+struct sk_buff *nf_reject_skb_v6_tcp_reset(struct net *net,
+					   struct sk_buff *oldskb,
+					   const struct net_device *dev,
+					   int hook);
+struct sk_buff *nf_reject_skb_v6_unreach(struct net *net,
+					 struct sk_buff *oldskb,
+					 const struct net_device *dev,
+					 int hook, u8 code);
+
 #endif /* _IPV6_NF_REJECT_H */

net/bridge/netfilter/Kconfig

···
 
 config NFT_BRIDGE_REJECT
 	tristate "Netfilter nf_tables bridge reject support"
-	depends on NFT_REJECT && NFT_REJECT_IPV4 && NFT_REJECT_IPV6
+	depends on NFT_REJECT
 	help
 	  Add support to reject packets.
 

net/bridge/netfilter/nft_reject_bridge.c

···
 	}
 }
 
-static int nft_bridge_iphdr_validate(struct sk_buff *skb)
-{
-	struct iphdr *iph;
-	u32 len;
-
-	if (!pskb_may_pull(skb, sizeof(struct iphdr)))
-		return 0;
-
-	iph = ip_hdr(skb);
-	if (iph->ihl < 5 || iph->version != 4)
-		return 0;
-
-	len = ntohs(iph->tot_len);
-	if (skb->len < len)
-		return 0;
-	else if (len < (iph->ihl*4))
-		return 0;
-
-	if (!pskb_may_pull(skb, iph->ihl*4))
-		return 0;
-
-	return 1;
-}
-
 /* We cannot use oldskb->dev, it can be either bridge device (NF_BRIDGE INPUT)
  * or the bridge port (NF_BRIDGE PREROUTING).
  */
···
 					    int hook)
 {
 	struct sk_buff *nskb;
-	struct iphdr *niph;
-	const struct tcphdr *oth;
-	struct tcphdr _oth;
 
-	if (!nft_bridge_iphdr_validate(oldskb))
-		return;
-
-	oth = nf_reject_ip_tcphdr_get(oldskb, &_oth, hook);
-	if (!oth)
-		return;
-
-	nskb = alloc_skb(sizeof(struct iphdr) + sizeof(struct tcphdr) +
-			 LL_MAX_HEADER, GFP_ATOMIC);
+	nskb = nf_reject_skb_v4_tcp_reset(net, oldskb, dev, hook);
 	if (!nskb)
 		return;
-
-	skb_reserve(nskb, LL_MAX_HEADER);
-	niph = nf_reject_iphdr_put(nskb, oldskb, IPPROTO_TCP,
-				   net->ipv4.sysctl_ip_default_ttl);
-	nf_reject_ip_tcphdr_put(nskb, oldskb, oth);
-	niph->tot_len = htons(nskb->len);
-	ip_send_check(niph);
 
 	nft_reject_br_push_etherhdr(oldskb, nskb);
 
···
 					  int hook, u8 code)
 {
 	struct sk_buff *nskb;
-	struct iphdr *niph;
-	struct icmphdr *icmph;
-	unsigned int len;
-	__wsum csum;
-	u8 proto;
 
-	if (!nft_bridge_iphdr_validate(oldskb))
-		return;
-
-	/* IP header checks: fragment. */
-	if (ip_hdr(oldskb)->frag_off & htons(IP_OFFSET))
-		return;
-
-	/* RFC says return as much as we can without exceeding 576 bytes. */
-	len = min_t(unsigned int, 536, oldskb->len);
-
-	if (!pskb_may_pull(oldskb, len))
-		return;
-
-	if (pskb_trim_rcsum(oldskb, ntohs(ip_hdr(oldskb)->tot_len)))
-		return;
-
-	proto = ip_hdr(oldskb)->protocol;
-
-	if (!skb_csum_unnecessary(oldskb) &&
-	    nf_reject_verify_csum(proto) &&
-	    nf_ip_checksum(oldskb, hook, ip_hdrlen(oldskb), proto))
-		return;
-
-	nskb = alloc_skb(sizeof(struct iphdr) + sizeof(struct icmphdr) +
-			 LL_MAX_HEADER + len, GFP_ATOMIC);
+	nskb = nf_reject_skb_v4_unreach(net, oldskb, dev, hook, code);
 	if (!nskb)
 		return;
-
-	skb_reserve(nskb, LL_MAX_HEADER);
-	niph = nf_reject_iphdr_put(nskb, oldskb, IPPROTO_ICMP,
-				   net->ipv4.sysctl_ip_default_ttl);
-
-	skb_reset_transport_header(nskb);
-	icmph = skb_put_zero(nskb, sizeof(struct icmphdr));
-	icmph->type     = ICMP_DEST_UNREACH;
-	icmph->code	= code;
-
-	skb_put_data(nskb, skb_network_header(oldskb), len);
-
-	csum = csum_partial((void *)icmph, len + sizeof(struct icmphdr), 0);
-	icmph->checksum = csum_fold(csum);
-
-	niph->tot_len	= htons(nskb->len);
-	ip_send_check(niph);
 
 	nft_reject_br_push_etherhdr(oldskb, nskb);
 
 	br_forward(br_port_get_rcu(dev), nskb, false, true);
-}
-
-static int nft_bridge_ip6hdr_validate(struct sk_buff *skb)
-{
-	struct ipv6hdr *hdr;
-	u32 pkt_len;
-
-	if (!pskb_may_pull(skb, sizeof(struct ipv6hdr)))
-		return 0;
-
-	hdr = ipv6_hdr(skb);
-	if (hdr->version != 6)
-		return 0;
-
-	pkt_len = ntohs(hdr->payload_len);
-	if (pkt_len + sizeof(struct ipv6hdr) > skb->len)
-		return 0;
-
-	return 1;
 }
 
 static void nft_reject_br_send_v6_tcp_reset(struct net *net,
···
 					    int hook)
 {
 	struct sk_buff *nskb;
-	const struct tcphdr *oth;
-	struct tcphdr _oth;
-	unsigned int otcplen;
-	struct ipv6hdr *nip6h;
 
-	if (!nft_bridge_ip6hdr_validate(oldskb))
-		return;
-
-	oth = nf_reject_ip6_tcphdr_get(oldskb, &_oth, &otcplen, hook);
-	if (!oth)
-		return;
-
-	nskb = alloc_skb(sizeof(struct ipv6hdr) + sizeof(struct tcphdr) +
-			 LL_MAX_HEADER, GFP_ATOMIC);
+	nskb = nf_reject_skb_v6_tcp_reset(net, oldskb, dev, hook);
 	if (!nskb)
 		return;
-
-	skb_reserve(nskb, LL_MAX_HEADER);
-	nip6h = nf_reject_ip6hdr_put(nskb, oldskb, IPPROTO_TCP,
-				     net->ipv6.devconf_all->hop_limit);
-	nf_reject_ip6_tcphdr_put(nskb, oldskb, oth, otcplen);
-	nip6h->payload_len = htons(nskb->len - sizeof(struct ipv6hdr));
 
 	nft_reject_br_push_etherhdr(oldskb, nskb);
 
 	br_forward(br_port_get_rcu(dev), nskb, false, true);
 }
 
-static bool reject6_br_csum_ok(struct sk_buff *skb, int hook)
-{
-	const struct ipv6hdr *ip6h = ipv6_hdr(skb);
-	int thoff;
-	__be16 fo;
-	u8 proto = ip6h->nexthdr;
-
-	if (skb_csum_unnecessary(skb))
-		return true;
-
-	if (ip6h->payload_len &&
-	    pskb_trim_rcsum(skb, ntohs(ip6h->payload_len) + sizeof(*ip6h)))
-		return false;
-
-	ip6h = ipv6_hdr(skb);
-	thoff = ipv6_skip_exthdr(skb, ((u8*)(ip6h+1) - skb->data), &proto, &fo);
-	if (thoff < 0 || thoff >= skb->len || (fo & htons(~0x7)) != 0)
-		return false;
-
-	if (!nf_reject_verify_csum(proto))
-		return true;
-
-	return nf_ip6_checksum(skb, hook, thoff, proto) == 0;
-}
 
 static void nft_reject_br_send_v6_unreach(struct net *net,
 					  struct sk_buff *oldskb,
···
 					  int hook, u8 code)
 {
 	struct sk_buff *nskb;
-	struct ipv6hdr *nip6h;
-	struct icmp6hdr *icmp6h;
-	unsigned int len;
 
-	if (!nft_bridge_ip6hdr_validate(oldskb))
-		return;
-
-	/* Include "As much of invoking packet as possible without the ICMPv6
-	 * packet exceeding the minimum IPv6 MTU" in the ICMP payload.
-	 */
-	len = min_t(unsigned int, 1220, oldskb->len);
-
-	if (!pskb_may_pull(oldskb, len))
-		return;
-
-	if (!reject6_br_csum_ok(oldskb, hook))
-		return;
-
-	nskb = alloc_skb(sizeof(struct ipv6hdr) + sizeof(struct icmp6hdr) +
-			 LL_MAX_HEADER + len, GFP_ATOMIC);
+	nskb = nf_reject_skb_v6_unreach(net, oldskb, dev, hook, code);
 	if (!nskb)
 		return;
-
-	skb_reserve(nskb, LL_MAX_HEADER);
-	nip6h = nf_reject_ip6hdr_put(nskb, oldskb, IPPROTO_ICMPV6,
-				     net->ipv6.devconf_all->hop_limit);
-
-	skb_reset_transport_header(nskb);
-	icmp6h = skb_put_zero(nskb, sizeof(struct icmp6hdr));
-	icmp6h->icmp6_type = ICMPV6_DEST_UNREACH;
-	icmp6h->icmp6_code = code;
-
-	skb_put_data(nskb, skb_network_header(oldskb), len);
-	nip6h->payload_len = htons(nskb->len - sizeof(struct ipv6hdr));
-
-	icmp6h->icmp6_cksum =
-		csum_ipv6_magic(&nip6h->saddr, &nip6h->daddr,
-				nskb->len - sizeof(struct ipv6hdr),
-				IPPROTO_ICMPV6,
-				csum_partial(icmp6h,
-					     nskb->len - sizeof(struct ipv6hdr),
-					     0));
 
 	nft_reject_br_push_etherhdr(oldskb, nskb);
 

net/ipv4/netfilter/nf_reject_ipv4.c

···
 #include <linux/netfilter_ipv4.h>
 #include <linux/netfilter_bridge.h>
 
+static int nf_reject_iphdr_validate(struct sk_buff *skb)
+{
+	struct iphdr *iph;
+	u32 len;
+
+	if (!pskb_may_pull(skb, sizeof(struct iphdr)))
+		return 0;
+
+	iph = ip_hdr(skb);
+	if (iph->ihl < 5 || iph->version != 4)
+		return 0;
+
+	len = ntohs(iph->tot_len);
+	if (skb->len < len)
+		return 0;
+	else if (len < (iph->ihl*4))
+		return 0;
+
+	if (!pskb_may_pull(skb, iph->ihl*4))
+		return 0;
+
+	return 1;
+}
+
+struct sk_buff *nf_reject_skb_v4_tcp_reset(struct net *net,
+					   struct sk_buff *oldskb,
+					   const struct net_device *dev,
+					   int hook)
+{
+	const struct tcphdr *oth;
+	struct sk_buff *nskb;
+	struct iphdr *niph;
+	struct tcphdr _oth;
+
+	if (!nf_reject_iphdr_validate(oldskb))
+		return NULL;
+
+	oth = nf_reject_ip_tcphdr_get(oldskb, &_oth, hook);
+	if (!oth)
+		return NULL;
+
+	nskb = alloc_skb(sizeof(struct iphdr) + sizeof(struct tcphdr) +
+			 LL_MAX_HEADER, GFP_ATOMIC);
+	if (!nskb)
+		return NULL;
+
+	nskb->dev = (struct net_device *)dev;
+
+	skb_reserve(nskb, LL_MAX_HEADER);
+	niph = nf_reject_iphdr_put(nskb, oldskb, IPPROTO_TCP,
+				   net->ipv4.sysctl_ip_default_ttl);
+	nf_reject_ip_tcphdr_put(nskb, oldskb, oth);
+	niph->tot_len = htons(nskb->len);
+	ip_send_check(niph);
+
+	return nskb;
+}
+EXPORT_SYMBOL_GPL(nf_reject_skb_v4_tcp_reset);
+
+struct sk_buff *nf_reject_skb_v4_unreach(struct net *net,
+					 struct sk_buff *oldskb,
+					 const struct net_device *dev,
+					 int hook, u8 code)
+{
+	struct sk_buff *nskb;
+	struct iphdr *niph;
+	struct icmphdr *icmph;
+	unsigned int len;
+	__wsum csum;
+	u8 proto;
+
+	if (!nf_reject_iphdr_validate(oldskb))
+		return NULL;
+
+	/* IP header checks: fragment. */
+	if (ip_hdr(oldskb)->frag_off & htons(IP_OFFSET))
+		return NULL;
+
+	/* RFC says return as much as we can without exceeding 576 bytes. */
+	len = min_t(unsigned int, 536, oldskb->len);
+
+	if (!pskb_may_pull(oldskb, len))
+		return NULL;
+
+	if (pskb_trim_rcsum(oldskb, ntohs(ip_hdr(oldskb)->tot_len)))
+		return NULL;
+
+	proto = ip_hdr(oldskb)->protocol;
+
+	if (!skb_csum_unnecessary(oldskb) &&
+	    nf_reject_verify_csum(proto) &&
+	    nf_ip_checksum(oldskb, hook, ip_hdrlen(oldskb), proto))
+		return NULL;
+
+	nskb = alloc_skb(sizeof(struct iphdr) + sizeof(struct icmphdr) +
+			 LL_MAX_HEADER + len, GFP_ATOMIC);
+	if (!nskb)
+		return NULL;
+
+	nskb->dev = (struct net_device *)dev;
+
+	skb_reserve(nskb, LL_MAX_HEADER);
+	niph = nf_reject_iphdr_put(nskb, oldskb, IPPROTO_ICMP,
+				   net->ipv4.sysctl_ip_default_ttl);
+
+	skb_reset_transport_header(nskb);
+	icmph = skb_put_zero(nskb, sizeof(struct icmphdr));
+	icmph->type     = ICMP_DEST_UNREACH;
+	icmph->code	= code;
+
+	skb_put_data(nskb, skb_network_header(oldskb), len);
+
+	csum = csum_partial((void *)icmph, len + sizeof(struct icmphdr), 0);
+	icmph->checksum = csum_fold(csum);
+
+	niph->tot_len	= htons(nskb->len);
+	ip_send_check(niph);
+
+	return nskb;
+}
+EXPORT_SYMBOL_GPL(nf_reject_skb_v4_unreach);
+
 const struct tcphdr *nf_reject_ip_tcphdr_get(struct sk_buff *oldskb,
 					     struct tcphdr *_oth, int hook)
 {

net/ipv6/netfilter/nf_reject_ipv6.c

···
 #include <linux/netfilter_ipv6.h>
 #include <linux/netfilter_bridge.h>
 
+static bool nf_reject_v6_csum_ok(struct sk_buff *skb, int hook)
+{
+	const struct ipv6hdr *ip6h = ipv6_hdr(skb);
+	int thoff;
+	__be16 fo;
+	u8 proto = ip6h->nexthdr;
+
+	if (skb_csum_unnecessary(skb))
+		return true;
+
+	if (ip6h->payload_len &&
+	    pskb_trim_rcsum(skb, ntohs(ip6h->payload_len) + sizeof(*ip6h)))
+		return false;
+
+	ip6h = ipv6_hdr(skb);
+	thoff = ipv6_skip_exthdr(skb, ((u8*)(ip6h+1) - skb->data), &proto, &fo);
+	if (thoff < 0 || thoff >= skb->len || (fo & htons(~0x7)) != 0)
+		return false;
+
+	if (!nf_reject_verify_csum(proto))
+		return true;
+
+	return nf_ip6_checksum(skb, hook, thoff, proto) == 0;
+}
+
+static int nf_reject_ip6hdr_validate(struct sk_buff *skb)
+{
+	struct ipv6hdr *hdr;
+	u32 pkt_len;
+
+	if (!pskb_may_pull(skb, sizeof(struct ipv6hdr)))
+		return 0;
+
+	hdr = ipv6_hdr(skb);
+	if (hdr->version != 6)
+		return 0;
+
+	pkt_len = ntohs(hdr->payload_len);
+	if (pkt_len + sizeof(struct ipv6hdr) > skb->len)
+		return 0;
+
+	return 1;
+}
+
+struct sk_buff *nf_reject_skb_v6_tcp_reset(struct net *net,
+					   struct sk_buff *oldskb,
+					   const struct net_device *dev,
+					   int hook)
+{
+	struct sk_buff *nskb;
+	const struct tcphdr *oth;
+	struct tcphdr _oth;
+	unsigned int otcplen;
+	struct ipv6hdr *nip6h;
+
+	if (!nf_reject_ip6hdr_validate(oldskb))
+		return NULL;
+
+	oth = nf_reject_ip6_tcphdr_get(oldskb, &_oth, &otcplen, hook);
+	if (!oth)
+		return NULL;
+
+	nskb = alloc_skb(sizeof(struct ipv6hdr) + sizeof(struct tcphdr) +
+			 LL_MAX_HEADER, GFP_ATOMIC);
+	if (!nskb)
+		return NULL;
+
+	nskb->dev = (struct net_device *)dev;
+
+	skb_reserve(nskb, LL_MAX_HEADER);
+	nip6h = nf_reject_ip6hdr_put(nskb, oldskb, IPPROTO_TCP,
+				     net->ipv6.devconf_all->hop_limit);
+	nf_reject_ip6_tcphdr_put(nskb, oldskb, oth, otcplen);
+	nip6h->payload_len = htons(nskb->len - sizeof(struct ipv6hdr));
+
+	return nskb;
+}
+EXPORT_SYMBOL_GPL(nf_reject_skb_v6_tcp_reset);
+
+struct sk_buff *nf_reject_skb_v6_unreach(struct net *net,
+					 struct sk_buff *oldskb,
+					 const struct net_device *dev,
+					 int hook, u8 code)
+{
+	struct sk_buff *nskb;
+	struct ipv6hdr *nip6h;
+	struct icmp6hdr *icmp6h;
+	unsigned int len;
+
+	if (!nf_reject_ip6hdr_validate(oldskb))
+		return NULL;
+
+	/* Include "As much of invoking packet as possible without the ICMPv6
+	 * packet exceeding the minimum IPv6 MTU" in the ICMP payload.
+	 */
+	len = min_t(unsigned int, 1220, oldskb->len);
+
+	if (!pskb_may_pull(oldskb, len))
+		return NULL;
+
+	if (!nf_reject_v6_csum_ok(oldskb, hook))
+		return NULL;
+
+	nskb = alloc_skb(sizeof(struct ipv6hdr) + sizeof(struct icmp6hdr) +
+			 LL_MAX_HEADER + len, GFP_ATOMIC);
+	if (!nskb)
+		return NULL;
+
+	nskb->dev = (struct net_device *)dev;
+
+	skb_reserve(nskb, LL_MAX_HEADER);
+	nip6h = nf_reject_ip6hdr_put(nskb, oldskb, IPPROTO_ICMPV6,
+				     net->ipv6.devconf_all->hop_limit);
+
+	skb_reset_transport_header(nskb);
+	icmp6h = skb_put_zero(nskb, sizeof(struct icmp6hdr));
+	icmp6h->icmp6_type = ICMPV6_DEST_UNREACH;
+	icmp6h->icmp6_code = code;
+
+	skb_put_data(nskb, skb_network_header(oldskb), len);
+	nip6h->payload_len = htons(nskb->len - sizeof(struct ipv6hdr));
+
+	icmp6h->icmp6_cksum =
+		csum_ipv6_magic(&nip6h->saddr, &nip6h->daddr,
+				nskb->len - sizeof(struct ipv6hdr),
+				IPPROTO_ICMPV6,
+				csum_partial(icmp6h,
+					     nskb->len - sizeof(struct ipv6hdr),
+					     0));
+
+	return nskb;
+}
+EXPORT_SYMBOL_GPL(nf_reject_skb_v6_unreach);
+
 const struct tcphdr *nf_reject_ip6_tcphdr_get(struct sk_buff *oldskb,
 					      struct tcphdr *otcph,
 					      unsigned int *otcplen, int hook)