1 files changed, 341 insertions, 0 deletions
diff --git a/net/ipv4/netfilter/nf_reject_ipv4.c b/net/ipv4/netfilter/nf_reject_ipv4.c
new file mode 100644
index 000000000..fc761915c
--- /dev/null
+++ b/net/ipv4/netfilter/nf_reject_ipv4.c
@@ -0,0 +1,341 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* (C) 1999-2001 Paul `Rusty' Russell
+ * (C) 2002-2004 Netfilter Core Team <coreteam@netfilter.org>
+ */
+
+#include <linux/module.h>
+#include <net/ip.h>
+#include <net/tcp.h>
+#include <net/route.h>
+#include <net/dst.h>
+#include <net/netfilter/ipv4/nf_reject.h>
+#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,
+				   READ_ONCE(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;
+	int dataoff;
+	__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;
+
+	dataoff = ip_hdrlen(oldskb);
+	proto = ip_hdr(oldskb)->protocol;
+
+	if (!skb_csum_unnecessary(oldskb) &&
+	    nf_reject_verify_csum(oldskb, dataoff, 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,
+				   READ_ONCE(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)
+{
+	const struct tcphdr *oth;
+
+	/* IP header checks: fragment. */
+	if (ip_hdr(oldskb)->frag_off & htons(IP_OFFSET))
+		return NULL;
+
+	if (ip_hdr(oldskb)->protocol != IPPROTO_TCP)
+		return NULL;
+
+	oth = skb_header_pointer(oldskb, ip_hdrlen(oldskb),
+				 sizeof(struct tcphdr), _oth);
+	if (oth == NULL)
+		return NULL;
+
+	/* No RST for RST. */
+	if (oth->rst)
+		return NULL;
+
+	/* Check checksum */
+	if (nf_ip_checksum(oldskb, hook, ip_hdrlen(oldskb), IPPROTO_TCP))
+		return NULL;
+
+	return oth;
+}
+EXPORT_SYMBOL_GPL(nf_reject_ip_tcphdr_get);
+
+struct iphdr *nf_reject_iphdr_put(struct sk_buff *nskb,
+				  const struct sk_buff *oldskb,
+				  __u8 protocol, int ttl)
+{
+	struct iphdr *niph, *oiph = ip_hdr(oldskb);
+
+	skb_reset_network_header(nskb);
+	niph = skb_put(nskb, sizeof(struct iphdr));
+	niph->version	= 4;
+	niph->ihl	= sizeof(struct iphdr) / 4;
+	niph->tos	= 0;
+	niph->id	= 0;
+	niph->frag_off	= htons(IP_DF);
+	niph->protocol	= protocol;
+	niph->check	= 0;
+	niph->saddr	= oiph->daddr;
+	niph->daddr	= oiph->saddr;
+	niph->ttl	= ttl;
+
+	nskb->protocol = htons(ETH_P_IP);
+
+	return niph;
+}
+EXPORT_SYMBOL_GPL(nf_reject_iphdr_put);
+
+void nf_reject_ip_tcphdr_put(struct sk_buff *nskb, const struct sk_buff *oldskb,
+			  const struct tcphdr *oth)
+{
+	struct iphdr *niph = ip_hdr(nskb);
+	struct tcphdr *tcph;
+
+	skb_reset_transport_header(nskb);
+	tcph = skb_put_zero(nskb, sizeof(struct tcphdr));
+	tcph->source	= oth->dest;
+	tcph->dest	= oth->source;
+	tcph->doff	= sizeof(struct tcphdr) / 4;
+
+	if (oth->ack) {
+		tcph->seq = oth->ack_seq;
+	} else {
+		tcph->ack_seq = htonl(ntohl(oth->seq) + oth->syn + oth->fin +
+				      oldskb->len - ip_hdrlen(oldskb) -
+				      (oth->doff << 2));
+		tcph->ack = 1;
+	}
+
+	tcph->rst	= 1;
+	tcph->check = ~tcp_v4_check(sizeof(struct tcphdr), niph->saddr,
+				    niph->daddr, 0);
+	nskb->ip_summed = CHECKSUM_PARTIAL;
+	nskb->csum_start = (unsigned char *)tcph - nskb->head;
+	nskb->csum_offset = offsetof(struct tcphdr, check);
+}
+EXPORT_SYMBOL_GPL(nf_reject_ip_tcphdr_put);
+
+static int nf_reject_fill_skb_dst(struct sk_buff *skb_in)
+{
+	struct dst_entry *dst = NULL;
+	struct flowi fl;
+
+	memset(&fl, 0, sizeof(struct flowi));
+	fl.u.ip4.daddr = ip_hdr(skb_in)->saddr;
+	nf_ip_route(dev_net(skb_in->dev), &dst, &fl, false);
+	if (!dst)
+		return -1;
+
+	skb_dst_set(skb_in, dst);
+	return 0;
+}
+
+/* Send RST reply */
+void nf_send_reset(struct net *net, struct sock *sk, struct sk_buff *oldskb,
+		   int hook)
+{
+	struct sk_buff *nskb;
+	struct iphdr *niph;
+	const struct tcphdr *oth;
+	struct tcphdr _oth;
+
+	oth = nf_reject_ip_tcphdr_get(oldskb, &_oth, hook);
+	if (!oth)
+		return;
+
+	if ((hook == NF_INET_PRE_ROUTING || hook == NF_INET_INGRESS) &&
+	    nf_reject_fill_skb_dst(oldskb) < 0)
+		return;
+
+	if (skb_rtable(oldskb)->rt_flags & (RTCF_BROADCAST | RTCF_MULTICAST))
+		return;
+
+	nskb = alloc_skb(sizeof(struct iphdr) + sizeof(struct tcphdr) +
+			 LL_MAX_HEADER, GFP_ATOMIC);
+	if (!nskb)
+		return;
+
+	/* ip_route_me_harder expects skb->dst to be set */
+	skb_dst_set_noref(nskb, skb_dst(oldskb));
+
+	nskb->mark = IP4_REPLY_MARK(net, oldskb->mark);
+
+	skb_reserve(nskb, LL_MAX_HEADER);
+	niph = nf_reject_iphdr_put(nskb, oldskb, IPPROTO_TCP,
+				   ip4_dst_hoplimit(skb_dst(nskb)));
+	nf_reject_ip_tcphdr_put(nskb, oldskb, oth);
+	if (ip_route_me_harder(net, sk, nskb, RTN_UNSPEC))
+		goto free_nskb;
+
+	niph = ip_hdr(nskb);
+
+	/* "Never happens" */
+	if (nskb->len > dst_mtu(skb_dst(nskb)))
+		goto free_nskb;
+
+	nf_ct_attach(nskb, oldskb);
+	nf_ct_set_closing(skb_nfct(oldskb));
+
+#if IS_ENABLED(CONFIG_BRIDGE_NETFILTER)
+	/* If we use ip_local_out for bridged traffic, the MAC source on
+	 * the RST will be ours, instead of the destination's.  This confuses
+	 * some routers/firewalls, and they drop the packet.  So we need to
+	 * build the eth header using the original destination's MAC as the
+	 * source, and send the RST packet directly.
+	 */
+	if (nf_bridge_info_exists(oldskb)) {
+		struct ethhdr *oeth = eth_hdr(oldskb);
+		struct net_device *br_indev;
+
+		br_indev = nf_bridge_get_physindev(oldskb, net);
+		if (!br_indev)
+			goto free_nskb;
+
+		nskb->dev = br_indev;
+		niph->tot_len = htons(nskb->len);
+		ip_send_check(niph);
+		if (dev_hard_header(nskb, nskb->dev, ntohs(nskb->protocol),
+				    oeth->h_source, oeth->h_dest, nskb->len) < 0)
+			goto free_nskb;
+		dev_queue_xmit(nskb);
+	} else
+#endif
+		ip_local_out(net, nskb->sk, nskb);
+
+	return;
+
+ free_nskb:
+	kfree_skb(nskb);
+}
+EXPORT_SYMBOL_GPL(nf_send_reset);
+
+void nf_send_unreach(struct sk_buff *skb_in, int code, int hook)
+{
+	struct iphdr *iph = ip_hdr(skb_in);
+	int dataoff = ip_hdrlen(skb_in);
+	u8 proto = iph->protocol;
+
+	if (iph->frag_off & htons(IP_OFFSET))
+		return;
+
+	if ((hook == NF_INET_PRE_ROUTING || hook == NF_INET_INGRESS) &&
+	    nf_reject_fill_skb_dst(skb_in) < 0)
+		return;
+
+	if (skb_csum_unnecessary(skb_in) ||
+	    !nf_reject_verify_csum(skb_in, dataoff, proto)) {
+		icmp_send(skb_in, ICMP_DEST_UNREACH, code, 0);
+		return;
+	}
+
+	if (nf_ip_checksum(skb_in, hook, dataoff, proto) == 0)
+		icmp_send(skb_in, ICMP_DEST_UNREACH, code, 0);
+}
+EXPORT_SYMBOL_GPL(nf_send_unreach);
+
+MODULE_LICENSE("GPL");