// SPDX-License-Identifier: GPL-2.0-only
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/* (C) 1999-2001 Paul `Rusty' Russell
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* (C) 2002-2004 Netfilter Core Team <coreteam@netfilter.org>
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*/
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#include <linux/module.h>
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#include <net/ip.h>
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#include <net/tcp.h>
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#include <net/route.h>
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#include <net/dst.h>
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#include <net/netfilter/ipv4/nf_reject.h>
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#include <linux/netfilter_ipv4.h>
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#include <linux/netfilter_bridge.h>
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const struct tcphdr *nf_reject_ip_tcphdr_get(struct sk_buff *oldskb,
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struct tcphdr *_oth, int hook)
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{
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const struct tcphdr *oth;
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/* IP header checks: fragment. */
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if (ip_hdr(oldskb)->frag_off & htons(IP_OFFSET))
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return NULL;
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if (ip_hdr(oldskb)->protocol != IPPROTO_TCP)
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return NULL;
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oth = skb_header_pointer(oldskb, ip_hdrlen(oldskb),
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sizeof(struct tcphdr), _oth);
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if (oth == NULL)
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return NULL;
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/* No RST for RST. */
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if (oth->rst)
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return NULL;
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/* Check checksum */
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if (nf_ip_checksum(oldskb, hook, ip_hdrlen(oldskb), IPPROTO_TCP))
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return NULL;
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return oth;
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}
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EXPORT_SYMBOL_GPL(nf_reject_ip_tcphdr_get);
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struct iphdr *nf_reject_iphdr_put(struct sk_buff *nskb,
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const struct sk_buff *oldskb,
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__u8 protocol, int ttl)
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{
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struct iphdr *niph, *oiph = ip_hdr(oldskb);
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skb_reset_network_header(nskb);
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niph = skb_put(nskb, sizeof(struct iphdr));
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niph->version = 4;
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niph->ihl = sizeof(struct iphdr) / 4;
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niph->tos = 0;
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niph->id = 0;
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niph->frag_off = htons(IP_DF);
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niph->protocol = protocol;
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niph->check = 0;
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niph->saddr = oiph->daddr;
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niph->daddr = oiph->saddr;
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niph->ttl = ttl;
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nskb->protocol = htons(ETH_P_IP);
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return niph;
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}
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EXPORT_SYMBOL_GPL(nf_reject_iphdr_put);
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void nf_reject_ip_tcphdr_put(struct sk_buff *nskb, const struct sk_buff *oldskb,
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const struct tcphdr *oth)
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{
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struct iphdr *niph = ip_hdr(nskb);
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struct tcphdr *tcph;
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skb_reset_transport_header(nskb);
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tcph = skb_put_zero(nskb, sizeof(struct tcphdr));
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tcph->source = oth->dest;
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tcph->dest = oth->source;
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tcph->doff = sizeof(struct tcphdr) / 4;
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if (oth->ack) {
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tcph->seq = oth->ack_seq;
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} else {
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tcph->ack_seq = htonl(ntohl(oth->seq) + oth->syn + oth->fin +
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oldskb->len - ip_hdrlen(oldskb) -
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(oth->doff << 2));
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tcph->ack = 1;
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}
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tcph->rst = 1;
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tcph->check = ~tcp_v4_check(sizeof(struct tcphdr), niph->saddr,
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niph->daddr, 0);
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nskb->ip_summed = CHECKSUM_PARTIAL;
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nskb->csum_start = (unsigned char *)tcph - nskb->head;
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nskb->csum_offset = offsetof(struct tcphdr, check);
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}
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EXPORT_SYMBOL_GPL(nf_reject_ip_tcphdr_put);
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static int nf_reject_fill_skb_dst(struct sk_buff *skb_in)
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{
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struct dst_entry *dst = NULL;
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struct flowi fl;
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memset(&fl, 0, sizeof(struct flowi));
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fl.u.ip4.daddr = ip_hdr(skb_in)->saddr;
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nf_ip_route(dev_net(skb_in->dev), &dst, &fl, false);
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if (!dst)
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return -1;
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skb_dst_set(skb_in, dst);
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return 0;
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}
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/* Send RST reply */
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void nf_send_reset(struct net *net, struct sk_buff *oldskb, int hook)
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{
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struct net_device *br_indev __maybe_unused;
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struct sk_buff *nskb;
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struct iphdr *niph;
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const struct tcphdr *oth;
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struct tcphdr _oth;
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oth = nf_reject_ip_tcphdr_get(oldskb, &_oth, hook);
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if (!oth)
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return;
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if (hook == NF_INET_PRE_ROUTING && nf_reject_fill_skb_dst(oldskb))
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return;
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if (skb_rtable(oldskb)->rt_flags & (RTCF_BROADCAST | RTCF_MULTICAST))
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return;
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nskb = alloc_skb(sizeof(struct iphdr) + sizeof(struct tcphdr) +
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LL_MAX_HEADER, GFP_ATOMIC);
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if (!nskb)
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return;
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/* ip_route_me_harder expects skb->dst to be set */
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skb_dst_set_noref(nskb, skb_dst(oldskb));
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nskb->mark = IP4_REPLY_MARK(net, oldskb->mark);
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skb_reserve(nskb, LL_MAX_HEADER);
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niph = nf_reject_iphdr_put(nskb, oldskb, IPPROTO_TCP,
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ip4_dst_hoplimit(skb_dst(nskb)));
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nf_reject_ip_tcphdr_put(nskb, oldskb, oth);
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if (ip_route_me_harder(net, nskb->sk, nskb, RTN_UNSPEC))
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goto free_nskb;
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niph = ip_hdr(nskb);
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/* "Never happens" */
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if (nskb->len > dst_mtu(skb_dst(nskb)))
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goto free_nskb;
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nf_ct_attach(nskb, oldskb);
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#if IS_ENABLED(CONFIG_BRIDGE_NETFILTER)
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/* If we use ip_local_out for bridged traffic, the MAC source on
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* the RST will be ours, instead of the destination's. This confuses
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* some routers/firewalls, and they drop the packet. So we need to
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* build the eth header using the original destination's MAC as the
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* source, and send the RST packet directly.
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*/
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br_indev = nf_bridge_get_physindev(oldskb);
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if (br_indev) {
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struct ethhdr *oeth = eth_hdr(oldskb);
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nskb->dev = br_indev;
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niph->tot_len = htons(nskb->len);
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ip_send_check(niph);
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if (dev_hard_header(nskb, nskb->dev, ntohs(nskb->protocol),
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oeth->h_source, oeth->h_dest, nskb->len) < 0)
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goto free_nskb;
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dev_queue_xmit(nskb);
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} else
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#endif
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ip_local_out(net, nskb->sk, nskb);
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return;
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free_nskb:
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kfree_skb(nskb);
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}
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EXPORT_SYMBOL_GPL(nf_send_reset);
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void nf_send_unreach(struct sk_buff *skb_in, int code, int hook)
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{
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struct iphdr *iph = ip_hdr(skb_in);
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u8 proto = iph->protocol;
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if (iph->frag_off & htons(IP_OFFSET))
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return;
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if (hook == NF_INET_PRE_ROUTING && nf_reject_fill_skb_dst(skb_in))
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return;
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if (skb_csum_unnecessary(skb_in) || !nf_reject_verify_csum(proto)) {
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icmp_send(skb_in, ICMP_DEST_UNREACH, code, 0);
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return;
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}
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if (nf_ip_checksum(skb_in, hook, ip_hdrlen(skb_in), proto) == 0)
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icmp_send(skb_in, ICMP_DEST_UNREACH, code, 0);
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}
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EXPORT_SYMBOL_GPL(nf_send_unreach);
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MODULE_LICENSE("GPL");
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