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- // 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>
- 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 sk_buff *oldskb, int hook)
- {
- struct net_device *br_indev __maybe_unused;
- 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 && nf_reject_fill_skb_dst(oldskb))
- 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, nskb->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);
- #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.
- */
- br_indev = nf_bridge_get_physindev(oldskb);
- if (br_indev) {
- struct ethhdr *oeth = eth_hdr(oldskb);
- 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);
- u8 proto = iph->protocol;
- if (iph->frag_off & htons(IP_OFFSET))
- return;
- if (hook == NF_INET_PRE_ROUTING && nf_reject_fill_skb_dst(skb_in))
- return;
- if (skb_csum_unnecessary(skb_in) || !nf_reject_verify_csum(proto)) {
- icmp_send(skb_in, ICMP_DEST_UNREACH, code, 0);
- return;
- }
- if (nf_ip_checksum(skb_in, hook, ip_hdrlen(skb_in), proto) == 0)
- icmp_send(skb_in, ICMP_DEST_UNREACH, code, 0);
- }
- EXPORT_SYMBOL_GPL(nf_send_unreach);
- MODULE_LICENSE("GPL");
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