1 /* (C) 1999-2001 Paul `Rusty' Russell
2 * (C) 2002-2004 Netfilter Core Team <coreteam@netfilter.org>
4 * This program is free software; you can redistribute it and/or modify
5 * it under the terms of the GNU General Public License version 2 as
6 * published by the Free Software Foundation.
9 #include <linux/module.h>
12 #include <net/route.h>
14 #include <net/netfilter/ipv4/nf_reject.h>
15 #include <linux/netfilter_ipv4.h>
18 void nf_send_reset(struct sk_buff *oldskb, int hook)
21 const struct iphdr *oiph;
23 const struct tcphdr *oth;
24 struct tcphdr _otcph, *tcph;
26 /* IP header checks: fragment. */
27 if (ip_hdr(oldskb)->frag_off & htons(IP_OFFSET))
30 oth = skb_header_pointer(oldskb, ip_hdrlen(oldskb),
31 sizeof(_otcph), &_otcph);
39 if (skb_rtable(oldskb)->rt_flags & (RTCF_BROADCAST | RTCF_MULTICAST))
43 if (nf_ip_checksum(oldskb, hook, ip_hdrlen(oldskb), IPPROTO_TCP))
45 oiph = ip_hdr(oldskb);
47 nskb = alloc_skb(sizeof(struct iphdr) + sizeof(struct tcphdr) +
48 LL_MAX_HEADER, GFP_ATOMIC);
52 skb_reserve(nskb, LL_MAX_HEADER);
54 skb_reset_network_header(nskb);
55 niph = (struct iphdr *)skb_put(nskb, sizeof(struct iphdr));
57 niph->ihl = sizeof(struct iphdr) / 4;
60 niph->frag_off = htons(IP_DF);
61 niph->protocol = IPPROTO_TCP;
63 niph->saddr = oiph->daddr;
64 niph->daddr = oiph->saddr;
66 skb_reset_transport_header(nskb);
67 tcph = (struct tcphdr *)skb_put(nskb, sizeof(struct tcphdr));
68 memset(tcph, 0, sizeof(*tcph));
69 tcph->source = oth->dest;
70 tcph->dest = oth->source;
71 tcph->doff = sizeof(struct tcphdr) / 4;
74 tcph->seq = oth->ack_seq;
76 tcph->ack_seq = htonl(ntohl(oth->seq) + oth->syn + oth->fin +
77 oldskb->len - ip_hdrlen(oldskb) -
83 tcph->check = ~tcp_v4_check(sizeof(struct tcphdr), niph->saddr,
85 nskb->ip_summed = CHECKSUM_PARTIAL;
86 nskb->csum_start = (unsigned char *)tcph - nskb->head;
87 nskb->csum_offset = offsetof(struct tcphdr, check);
89 /* ip_route_me_harder expects skb->dst to be set */
90 skb_dst_set_noref(nskb, skb_dst(oldskb));
92 nskb->protocol = htons(ETH_P_IP);
93 if (ip_route_me_harder(nskb, RTN_UNSPEC))
96 niph->ttl = ip4_dst_hoplimit(skb_dst(nskb));
99 if (nskb->len > dst_mtu(skb_dst(nskb)))
102 nf_ct_attach(nskb, oldskb);
104 #if IS_ENABLED(CONFIG_BRIDGE_NETFILTER)
105 /* If we use ip_local_out for bridged traffic, the MAC source on
106 * the RST will be ours, instead of the destination's. This confuses
107 * some routers/firewalls, and they drop the packet. So we need to
108 * build the eth header using the original destination's MAC as the
109 * source, and send the RST packet directly.
111 if (oldskb->nf_bridge) {
112 struct ethhdr *oeth = eth_hdr(oldskb);
113 nskb->dev = oldskb->nf_bridge->physindev;
114 niph->tot_len = htons(nskb->len);
116 if (dev_hard_header(nskb, nskb->dev, ntohs(nskb->protocol),
117 oeth->h_source, oeth->h_dest, nskb->len) < 0)
119 dev_queue_xmit(nskb);
129 EXPORT_SYMBOL_GPL(nf_send_reset);
131 MODULE_LICENSE("GPL");