| /* |
| * This is a module which is used for rejecting packets. |
| */ |
| |
| /* (C) 1999-2001 Paul `Rusty' Russell |
| * (C) 2002-2004 Netfilter Core Team <coreteam@netfilter.org> |
| * |
| * This program is free software; you can redistribute it and/or modify |
| * it under the terms of the GNU General Public License version 2 as |
| * published by the Free Software Foundation. |
| */ |
| |
| #include <linux/module.h> |
| #include <linux/skbuff.h> |
| #include <linux/ip.h> |
| #include <linux/udp.h> |
| #include <linux/icmp.h> |
| #include <net/icmp.h> |
| #include <net/ip.h> |
| #include <net/tcp.h> |
| #include <net/route.h> |
| #include <net/dst.h> |
| #include <linux/netfilter/x_tables.h> |
| #include <linux/netfilter_ipv4/ip_tables.h> |
| #include <linux/netfilter_ipv4/ipt_REJECT.h> |
| #ifdef CONFIG_BRIDGE_NETFILTER |
| #include <linux/netfilter_bridge.h> |
| #endif |
| |
| MODULE_LICENSE("GPL"); |
| MODULE_AUTHOR("Netfilter Core Team <coreteam@netfilter.org>"); |
| MODULE_DESCRIPTION("iptables REJECT target module"); |
| |
| /* Send RST reply */ |
| static void send_reset(struct sk_buff *oldskb, int hook) |
| { |
| struct sk_buff *nskb; |
| struct iphdr *niph; |
| struct tcphdr _otcph, *oth, *tcph; |
| __be16 tmp_port; |
| __be32 tmp_addr; |
| int needs_ack; |
| unsigned int addr_type; |
| |
| /* IP header checks: fragment. */ |
| if (ip_hdr(oldskb)->frag_off & htons(IP_OFFSET)) |
| return; |
| |
| oth = skb_header_pointer(oldskb, ip_hdrlen(oldskb), |
| sizeof(_otcph), &_otcph); |
| if (oth == NULL) |
| return; |
| |
| /* No RST for RST. */ |
| if (oth->rst) |
| return; |
| |
| /* Check checksum */ |
| if (nf_ip_checksum(oldskb, hook, ip_hdrlen(oldskb), IPPROTO_TCP)) |
| return; |
| |
| /* We need a linear, writeable skb. We also need to expand |
| headroom in case hh_len of incoming interface < hh_len of |
| outgoing interface */ |
| nskb = skb_copy_expand(oldskb, LL_MAX_HEADER, skb_tailroom(oldskb), |
| GFP_ATOMIC); |
| if (!nskb) |
| return; |
| |
| /* This packet will not be the same as the other: clear nf fields */ |
| nf_reset(nskb); |
| nskb->mark = 0; |
| skb_init_secmark(nskb); |
| |
| skb_shinfo(nskb)->gso_size = 0; |
| skb_shinfo(nskb)->gso_segs = 0; |
| skb_shinfo(nskb)->gso_type = 0; |
| |
| tcph = (struct tcphdr *)(skb_network_header(nskb) + ip_hdrlen(nskb)); |
| |
| /* Swap source and dest */ |
| niph = ip_hdr(nskb); |
| tmp_addr = niph->saddr; |
| niph->saddr = niph->daddr; |
| niph->daddr = tmp_addr; |
| tmp_port = tcph->source; |
| tcph->source = tcph->dest; |
| tcph->dest = tmp_port; |
| |
| /* Truncate to length (no data) */ |
| tcph->doff = sizeof(struct tcphdr)/4; |
| skb_trim(nskb, ip_hdrlen(nskb) + sizeof(struct tcphdr)); |
| |
| if (tcph->ack) { |
| needs_ack = 0; |
| tcph->seq = oth->ack_seq; |
| tcph->ack_seq = 0; |
| } else { |
| needs_ack = 1; |
| tcph->ack_seq = htonl(ntohl(oth->seq) + oth->syn + oth->fin + |
| oldskb->len - ip_hdrlen(oldskb) - |
| (oth->doff << 2)); |
| tcph->seq = 0; |
| } |
| |
| /* Reset flags */ |
| ((u_int8_t *)tcph)[13] = 0; |
| tcph->rst = 1; |
| tcph->ack = needs_ack; |
| |
| tcph->window = 0; |
| tcph->urg_ptr = 0; |
| |
| /* Adjust TCP checksum */ |
| tcph->check = 0; |
| tcph->check = tcp_v4_check(sizeof(struct tcphdr), |
| niph->saddr, niph->daddr, |
| csum_partial(tcph, |
| sizeof(struct tcphdr), 0)); |
| |
| /* Set DF, id = 0 */ |
| niph->frag_off = htons(IP_DF); |
| niph->id = 0; |
| |
| addr_type = RTN_UNSPEC; |
| if (hook != NF_INET_FORWARD |
| #ifdef CONFIG_BRIDGE_NETFILTER |
| || (nskb->nf_bridge && nskb->nf_bridge->mask & BRNF_BRIDGED) |
| #endif |
| ) |
| addr_type = RTN_LOCAL; |
| |
| if (ip_route_me_harder(nskb, addr_type)) |
| goto free_nskb; |
| |
| nskb->ip_summed = CHECKSUM_NONE; |
| |
| /* Adjust IP TTL */ |
| niph->ttl = dst_metric(nskb->dst, RTAX_HOPLIMIT); |
| |
| /* "Never happens" */ |
| if (nskb->len > dst_mtu(nskb->dst)) |
| goto free_nskb; |
| |
| nf_ct_attach(nskb, oldskb); |
| |
| ip_local_out(nskb); |
| return; |
| |
| free_nskb: |
| kfree_skb(nskb); |
| } |
| |
| static inline void send_unreach(struct sk_buff *skb_in, int code) |
| { |
| icmp_send(skb_in, ICMP_DEST_UNREACH, code, 0); |
| } |
| |
| static unsigned int |
| reject_tg(struct sk_buff *skb, const struct net_device *in, |
| const struct net_device *out, unsigned int hooknum, |
| const struct xt_target *target, const void *targinfo) |
| { |
| const struct ipt_reject_info *reject = targinfo; |
| |
| /* Our naive response construction doesn't deal with IP |
| options, and probably shouldn't try. */ |
| if (ip_hdrlen(skb) != sizeof(struct iphdr)) |
| return NF_DROP; |
| |
| /* WARNING: This code causes reentry within iptables. |
| This means that the iptables jump stack is now crap. We |
| must return an absolute verdict. --RR */ |
| switch (reject->with) { |
| case IPT_ICMP_NET_UNREACHABLE: |
| send_unreach(skb, ICMP_NET_UNREACH); |
| break; |
| case IPT_ICMP_HOST_UNREACHABLE: |
| send_unreach(skb, ICMP_HOST_UNREACH); |
| break; |
| case IPT_ICMP_PROT_UNREACHABLE: |
| send_unreach(skb, ICMP_PROT_UNREACH); |
| break; |
| case IPT_ICMP_PORT_UNREACHABLE: |
| send_unreach(skb, ICMP_PORT_UNREACH); |
| break; |
| case IPT_ICMP_NET_PROHIBITED: |
| send_unreach(skb, ICMP_NET_ANO); |
| break; |
| case IPT_ICMP_HOST_PROHIBITED: |
| send_unreach(skb, ICMP_HOST_ANO); |
| break; |
| case IPT_ICMP_ADMIN_PROHIBITED: |
| send_unreach(skb, ICMP_PKT_FILTERED); |
| break; |
| case IPT_TCP_RESET: |
| send_reset(skb, hooknum); |
| case IPT_ICMP_ECHOREPLY: |
| /* Doesn't happen. */ |
| break; |
| } |
| |
| return NF_DROP; |
| } |
| |
| static bool |
| reject_tg_check(const char *tablename, const void *e_void, |
| const struct xt_target *target, void *targinfo, |
| unsigned int hook_mask) |
| { |
| const struct ipt_reject_info *rejinfo = targinfo; |
| const struct ipt_entry *e = e_void; |
| |
| if (rejinfo->with == IPT_ICMP_ECHOREPLY) { |
| printk("ipt_REJECT: ECHOREPLY no longer supported.\n"); |
| return false; |
| } else if (rejinfo->with == IPT_TCP_RESET) { |
| /* Must specify that it's a TCP packet */ |
| if (e->ip.proto != IPPROTO_TCP |
| || (e->ip.invflags & XT_INV_PROTO)) { |
| printk("ipt_REJECT: TCP_RESET invalid for non-tcp\n"); |
| return false; |
| } |
| } |
| return true; |
| } |
| |
| static struct xt_target reject_tg_reg __read_mostly = { |
| .name = "REJECT", |
| .family = AF_INET, |
| .target = reject_tg, |
| .targetsize = sizeof(struct ipt_reject_info), |
| .table = "filter", |
| .hooks = (1 << NF_INET_LOCAL_IN) | (1 << NF_INET_FORWARD) | |
| (1 << NF_INET_LOCAL_OUT), |
| .checkentry = reject_tg_check, |
| .me = THIS_MODULE, |
| }; |
| |
| static int __init reject_tg_init(void) |
| { |
| return xt_register_target(&reject_tg_reg); |
| } |
| |
| static void __exit reject_tg_exit(void) |
| { |
| xt_unregister_target(&reject_tg_reg); |
| } |
| |
| module_init(reject_tg_init); |
| module_exit(reject_tg_exit); |