/* * This is a module which is used for rejecting packets. * Added support for customized reject packets (Jozsef Kadlecsik). * Added support for ICMP type-3-code-13 (Maciej Soltysiak). [RFC 1812] */ /* (C) 1999-2001 Paul `Rusty' Russell * (C) 2002-2004 Netfilter Core Team * * 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 #include #include #include #include #include #include #include #include #include #include #include #include #ifdef CONFIG_BRIDGE_NETFILTER #include #endif MODULE_LICENSE("GPL"); MODULE_AUTHOR("Netfilter Core Team "); MODULE_DESCRIPTION("iptables REJECT target module"); #if 0 #define DEBUGP printk #else #define DEBUGP(format, args...) #endif /* Send RST reply */ static void send_reset(struct sk_buff *oldskb, int hook) { struct sk_buff *nskb; struct iphdr *iph = oldskb->nh.iph; struct tcphdr _otcph, *oth, *tcph; __be16 tmp_port; __be32 tmp_addr; int needs_ack; unsigned int addr_type; /* IP header checks: fragment. */ if (oldskb->nh.iph->frag_off & htons(IP_OFFSET)) return; oth = skb_header_pointer(oldskb, oldskb->nh.iph->ihl * 4, sizeof(_otcph), &_otcph); if (oth == NULL) return; /* No RST for RST. */ if (oth->rst) return; /* Check checksum */ if (nf_ip_checksum(oldskb, hook, iph->ihl * 4, 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); tcph = (struct tcphdr *)((u_int32_t*)nskb->nh.iph + nskb->nh.iph->ihl); /* Swap source and dest */ tmp_addr = nskb->nh.iph->saddr; nskb->nh.iph->saddr = nskb->nh.iph->daddr; nskb->nh.iph->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, nskb->nh.iph->ihl*4 + sizeof(struct tcphdr)); nskb->nh.iph->tot_len = htons(nskb->len); 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 - oldskb->nh.iph->ihl*4 - (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), nskb->nh.iph->saddr, nskb->nh.iph->daddr, csum_partial((char *)tcph, sizeof(struct tcphdr), 0)); /* Set DF, id = 0 */ nskb->nh.iph->frag_off = htons(IP_DF); nskb->nh.iph->id = 0; addr_type = RTN_UNSPEC; if (hook != NF_IP_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 */ nskb->nh.iph->ttl = dst_metric(nskb->dst, RTAX_HOPLIMIT); /* Adjust IP checksum */ nskb->nh.iph->check = 0; nskb->nh.iph->check = ip_fast_csum((unsigned char *)nskb->nh.iph, nskb->nh.iph->ihl); /* "Never happens" */ if (nskb->len > dst_mtu(nskb->dst)) goto free_nskb; nf_ct_attach(nskb, oldskb); NF_HOOK(PF_INET, NF_IP_LOCAL_OUT, nskb, NULL, nskb->dst->dev, dst_output); 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(struct sk_buff **pskb, 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 ((*pskb)->nh.iph->ihl<<2 != 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(*pskb, ICMP_NET_UNREACH); break; case IPT_ICMP_HOST_UNREACHABLE: send_unreach(*pskb, ICMP_HOST_UNREACH); break; case IPT_ICMP_PROT_UNREACHABLE: send_unreach(*pskb, ICMP_PROT_UNREACH); break; case IPT_ICMP_PORT_UNREACHABLE: send_unreach(*pskb, ICMP_PORT_UNREACH); break; case IPT_ICMP_NET_PROHIBITED: send_unreach(*pskb, ICMP_NET_ANO); break; case IPT_ICMP_HOST_PROHIBITED: send_unreach(*pskb, ICMP_HOST_ANO); break; case IPT_ICMP_ADMIN_PROHIBITED: send_unreach(*pskb, ICMP_PKT_FILTERED); break; case IPT_TCP_RESET: send_reset(*pskb, hooknum); case IPT_ICMP_ECHOREPLY: /* Doesn't happen. */ break; } return NF_DROP; } static int 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("REJECT: ECHOREPLY no longer supported.\n"); return 0; } 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)) { DEBUGP("REJECT: TCP_RESET invalid for non-tcp\n"); return 0; } } return 1; } static struct xt_target ipt_reject_reg = { .name = "REJECT", .family = AF_INET, .target = reject, .targetsize = sizeof(struct ipt_reject_info), .table = "filter", .hooks = (1 << NF_IP_LOCAL_IN) | (1 << NF_IP_FORWARD) | (1 << NF_IP_LOCAL_OUT), .checkentry = check, .me = THIS_MODULE, }; static int __init ipt_reject_init(void) { return xt_register_target(&ipt_reject_reg); } static void __exit ipt_reject_fini(void) { xt_unregister_target(&ipt_reject_reg); } module_init(ipt_reject_init); module_exit(ipt_reject_fini);