![Stanislav Fomichev](/assets/img/avatar_default.png)
Don't verify checksum for outgoing packets because checksum calculation may be done by the device. Without this patch: $ ip6tables -I OUTPUT -p tcp --dport 80 -j REJECT --reject-with tcp-reset $ time telnet ipv6.google.com 80 Trying 2a00:1450:4010:c03::67... telnet: Unable to connect to remote host: Connection timed out real 0m7.201s user 0m0.000s sys 0m0.000s With the patch applied: $ ip6tables -I OUTPUT -p tcp --dport 80 -j REJECT --reject-with tcp-reset $ time telnet ipv6.google.com 80 Trying 2a00:1450:4010:c03::67... telnet: Unable to connect to remote host: Connection refused real 0m0.085s user 0m0.000s sys 0m0.000s Signed-off-by: Stanislav Fomichev <stfomichev@yandex-team.ru> Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
282 lines
7.5 KiB
C
282 lines
7.5 KiB
C
/*
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* IP6 tables REJECT target module
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* Linux INET6 implementation
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*
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* Copyright (C)2003 USAGI/WIDE Project
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*
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* Authors:
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* Yasuyuki Kozakai <yasuyuki.kozakai@toshiba.co.jp>
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*
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* Copyright (c) 2005-2007 Patrick McHardy <kaber@trash.net>
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*
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* Based on net/ipv4/netfilter/ipt_REJECT.c
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version
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* 2 of the License, or (at your option) any later version.
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*/
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#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
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#include <linux/gfp.h>
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#include <linux/module.h>
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#include <linux/skbuff.h>
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#include <linux/icmpv6.h>
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#include <linux/netdevice.h>
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#include <net/ipv6.h>
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#include <net/tcp.h>
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#include <net/icmp.h>
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#include <net/ip6_checksum.h>
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#include <net/ip6_fib.h>
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#include <net/ip6_route.h>
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#include <net/flow.h>
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#include <linux/netfilter/x_tables.h>
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#include <linux/netfilter_ipv6/ip6_tables.h>
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#include <linux/netfilter_ipv6/ip6t_REJECT.h>
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MODULE_AUTHOR("Yasuyuki KOZAKAI <yasuyuki.kozakai@toshiba.co.jp>");
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MODULE_DESCRIPTION("Xtables: packet \"rejection\" target for IPv6");
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MODULE_LICENSE("GPL");
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/* Send RST reply */
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static void send_reset(struct net *net, struct sk_buff *oldskb, int hook)
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{
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struct sk_buff *nskb;
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struct tcphdr otcph, *tcph;
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unsigned int otcplen, hh_len;
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int tcphoff, needs_ack;
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const struct ipv6hdr *oip6h = ipv6_hdr(oldskb);
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struct ipv6hdr *ip6h;
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#define DEFAULT_TOS_VALUE 0x0U
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const __u8 tclass = DEFAULT_TOS_VALUE;
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struct dst_entry *dst = NULL;
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u8 proto;
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__be16 frag_off;
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struct flowi6 fl6;
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if ((!(ipv6_addr_type(&oip6h->saddr) & IPV6_ADDR_UNICAST)) ||
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(!(ipv6_addr_type(&oip6h->daddr) & IPV6_ADDR_UNICAST))) {
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pr_debug("addr is not unicast.\n");
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return;
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}
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proto = oip6h->nexthdr;
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tcphoff = ipv6_skip_exthdr(oldskb, ((u8*)(oip6h+1) - oldskb->data), &proto, &frag_off);
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if ((tcphoff < 0) || (tcphoff > oldskb->len)) {
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pr_debug("Cannot get TCP header.\n");
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return;
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}
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otcplen = oldskb->len - tcphoff;
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/* IP header checks: fragment, too short. */
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if (proto != IPPROTO_TCP || otcplen < sizeof(struct tcphdr)) {
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pr_debug("proto(%d) != IPPROTO_TCP, "
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"or too short. otcplen = %d\n",
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proto, otcplen);
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return;
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}
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if (skb_copy_bits(oldskb, tcphoff, &otcph, sizeof(struct tcphdr)))
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BUG();
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/* No RST for RST. */
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if (otcph.rst) {
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pr_debug("RST is set\n");
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return;
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}
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/* Check checksum. */
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if (nf_ip6_checksum(oldskb, hook, tcphoff, IPPROTO_TCP)) {
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pr_debug("TCP checksum is invalid\n");
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return;
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}
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memset(&fl6, 0, sizeof(fl6));
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fl6.flowi6_proto = IPPROTO_TCP;
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fl6.saddr = oip6h->daddr;
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fl6.daddr = oip6h->saddr;
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fl6.fl6_sport = otcph.dest;
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fl6.fl6_dport = otcph.source;
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security_skb_classify_flow(oldskb, flowi6_to_flowi(&fl6));
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dst = ip6_route_output(net, NULL, &fl6);
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if (dst == NULL || dst->error) {
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dst_release(dst);
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return;
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}
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dst = xfrm_lookup(net, dst, flowi6_to_flowi(&fl6), NULL, 0);
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if (IS_ERR(dst))
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return;
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hh_len = (dst->dev->hard_header_len + 15)&~15;
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nskb = alloc_skb(hh_len + 15 + dst->header_len + sizeof(struct ipv6hdr)
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+ sizeof(struct tcphdr) + dst->trailer_len,
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GFP_ATOMIC);
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if (!nskb) {
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net_dbg_ratelimited("cannot alloc skb\n");
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dst_release(dst);
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return;
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}
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skb_dst_set(nskb, dst);
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skb_reserve(nskb, hh_len + dst->header_len);
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skb_put(nskb, sizeof(struct ipv6hdr));
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skb_reset_network_header(nskb);
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ip6h = ipv6_hdr(nskb);
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ip6_flow_hdr(ip6h, tclass, 0);
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ip6h->hop_limit = ip6_dst_hoplimit(dst);
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ip6h->nexthdr = IPPROTO_TCP;
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ip6h->saddr = oip6h->daddr;
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ip6h->daddr = oip6h->saddr;
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skb_reset_transport_header(nskb);
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tcph = (struct tcphdr *)skb_put(nskb, sizeof(struct tcphdr));
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/* Truncate to length (no data) */
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tcph->doff = sizeof(struct tcphdr)/4;
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tcph->source = otcph.dest;
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tcph->dest = otcph.source;
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if (otcph.ack) {
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needs_ack = 0;
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tcph->seq = otcph.ack_seq;
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tcph->ack_seq = 0;
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} else {
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needs_ack = 1;
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tcph->ack_seq = htonl(ntohl(otcph.seq) + otcph.syn + otcph.fin
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+ otcplen - (otcph.doff<<2));
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tcph->seq = 0;
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}
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/* Reset flags */
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((u_int8_t *)tcph)[13] = 0;
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tcph->rst = 1;
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tcph->ack = needs_ack;
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tcph->window = 0;
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tcph->urg_ptr = 0;
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tcph->check = 0;
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/* Adjust TCP checksum */
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tcph->check = csum_ipv6_magic(&ipv6_hdr(nskb)->saddr,
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&ipv6_hdr(nskb)->daddr,
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sizeof(struct tcphdr), IPPROTO_TCP,
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csum_partial(tcph,
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sizeof(struct tcphdr), 0));
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nf_ct_attach(nskb, oldskb);
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#ifdef CONFIG_BRIDGE_NETFILTER
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/* If we use ip6_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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if (oldskb->nf_bridge) {
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struct ethhdr *oeth = eth_hdr(oldskb);
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nskb->dev = oldskb->nf_bridge->physindev;
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nskb->protocol = htons(ETH_P_IPV6);
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ip6h->payload_len = htons(sizeof(struct tcphdr));
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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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return;
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dev_queue_xmit(nskb);
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} else
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#endif
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ip6_local_out(nskb);
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}
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static inline void
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send_unreach(struct net *net, struct sk_buff *skb_in, unsigned char code,
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unsigned int hooknum)
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{
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if (hooknum == NF_INET_LOCAL_OUT && skb_in->dev == NULL)
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skb_in->dev = net->loopback_dev;
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icmpv6_send(skb_in, ICMPV6_DEST_UNREACH, code, 0);
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}
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static unsigned int
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reject_tg6(struct sk_buff *skb, const struct xt_action_param *par)
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{
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const struct ip6t_reject_info *reject = par->targinfo;
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struct net *net = dev_net((par->in != NULL) ? par->in : par->out);
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pr_debug("%s: medium point\n", __func__);
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switch (reject->with) {
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case IP6T_ICMP6_NO_ROUTE:
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send_unreach(net, skb, ICMPV6_NOROUTE, par->hooknum);
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break;
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case IP6T_ICMP6_ADM_PROHIBITED:
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send_unreach(net, skb, ICMPV6_ADM_PROHIBITED, par->hooknum);
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break;
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case IP6T_ICMP6_NOT_NEIGHBOUR:
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send_unreach(net, skb, ICMPV6_NOT_NEIGHBOUR, par->hooknum);
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break;
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case IP6T_ICMP6_ADDR_UNREACH:
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send_unreach(net, skb, ICMPV6_ADDR_UNREACH, par->hooknum);
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break;
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case IP6T_ICMP6_PORT_UNREACH:
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send_unreach(net, skb, ICMPV6_PORT_UNREACH, par->hooknum);
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break;
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case IP6T_ICMP6_ECHOREPLY:
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/* Do nothing */
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break;
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case IP6T_TCP_RESET:
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send_reset(net, skb, par->hooknum);
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break;
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default:
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net_info_ratelimited("case %u not handled yet\n", reject->with);
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break;
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}
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return NF_DROP;
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}
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static int reject_tg6_check(const struct xt_tgchk_param *par)
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{
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const struct ip6t_reject_info *rejinfo = par->targinfo;
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const struct ip6t_entry *e = par->entryinfo;
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if (rejinfo->with == IP6T_ICMP6_ECHOREPLY) {
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pr_info("ECHOREPLY is not supported.\n");
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return -EINVAL;
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} else if (rejinfo->with == IP6T_TCP_RESET) {
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/* Must specify that it's a TCP packet */
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if (e->ipv6.proto != IPPROTO_TCP ||
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(e->ipv6.invflags & XT_INV_PROTO)) {
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pr_info("TCP_RESET illegal for non-tcp\n");
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return -EINVAL;
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}
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}
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return 0;
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}
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static struct xt_target reject_tg6_reg __read_mostly = {
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.name = "REJECT",
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.family = NFPROTO_IPV6,
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.target = reject_tg6,
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.targetsize = sizeof(struct ip6t_reject_info),
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.table = "filter",
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.hooks = (1 << NF_INET_LOCAL_IN) | (1 << NF_INET_FORWARD) |
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(1 << NF_INET_LOCAL_OUT),
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.checkentry = reject_tg6_check,
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.me = THIS_MODULE
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};
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static int __init reject_tg6_init(void)
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{
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return xt_register_target(&reject_tg6_reg);
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}
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static void __exit reject_tg6_exit(void)
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{
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xt_unregister_target(&reject_tg6_reg);
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}
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module_init(reject_tg6_init);
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module_exit(reject_tg6_exit);
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