/* * Handle firewalling * Linux ethernet bridge * * Authors: * Lennert Buytenhek * Bart De Schuymer * * $Id: br_netfilter.c,v 1.4 2002/10/21 17:38:16 bdschuym Exp $ * * This program is free software; you can redistribute it and/or * modify it under the terms of the GNU General Public License * as published by the Free Software Foundation; either version * 2 of the License, or (at your option) any later version. * * Lennert dedicates this file to Kerstin Wurdinger. */ #include #include #include #include #include #include #include #include #include #include #include #include #include "br_private.h" #define skb_origaddr(skb) (((struct bridge_skb_cb *) \ (skb->cb))->daddr.ipv4) #define store_orig_dstaddr(skb) (skb_origaddr(skb) = (skb)->nh.iph->daddr) #define dnat_took_place(skb) (skb_origaddr(skb) != (skb)->nh.iph->daddr) #define clear_cb(skb) (memset(&skb_origaddr(skb), 0, \ sizeof(struct bridge_skb_cb))) #define has_bridge_parent(device) ((device)->br_port != NULL) #define bridge_parent(device) (&((device)->br_port->br->dev)) /* We need these fake structures to make netfilter happy -- * lots of places assume that skb->dst != NULL, which isn't * all that unreasonable. * * Currently, we fill in the PMTU entry because netfilter * refragmentation needs it, and the rt_flags entry because * ipt_REJECT needs it. Future netfilter modules might * require us to fill additional fields. */ static struct net_device __fake_net_device = { hard_header_len: ETH_HLEN }; static struct rtable __fake_rtable = { u: { dst: { __refcnt: ATOMIC_INIT(1), dev: &__fake_net_device, pmtu: 1500 } }, rt_flags: 0 }; /* PF_BRIDGE/PRE_ROUTING *********************************************/ static void __br_dnat_complain(void) { static unsigned long last_complaint = 0; if (jiffies - last_complaint >= 5 * HZ) { printk(KERN_WARNING "Performing cross-bridge DNAT requires IP " "forwarding to be enabled\n"); last_complaint = jiffies; } } /* This requires some explaining. If DNAT has taken place, * we will need to fix up the destination Ethernet address, * and this is a tricky process. * * There are two cases to consider: * 1. The packet was DNAT'ed to a device in the same bridge * port group as it was received on. We can still bridge * the packet. * 2. The packet was DNAT'ed to a different device, either * a non-bridged device or another bridge port group. * The packet will need to be routed. * * The correct way of distinguishing between these two cases is to * call ip_route_input() and to look at skb->dst->dev, which is * changed to the destination device if ip_route_input() succeeds. * * Let us first consider the case that ip_route_input() succeeds: * * If skb->dst->dev equals the logical bridge device the packet * came in on, we can consider this bridging. We then call * skb->dst->output() which will make the packet enter br_nf_local_out() * not much later. In that function it is assured that the iptables * FORWARD chain is traversed for the packet. * * Otherwise, the packet is considered to be routed and we just * change the destination MAC address so that the packet will * later be passed up to the IP stack to be routed. * * Let us now consider the case that ip_route_input() fails: * * After a "echo '0' > /proc/sys/net/ipv4/ip_forward" ip_route_input() * will fail, while ip_route_output() will return success. The source * address for ip_route_output() is set to zero, so ip_route_output() * thinks we're handling a locally generated packet and won't care * if IP forwarding is allowed. We send a warning message to the users's * log telling her to put IP forwarding on. * * ip_route_input() will also fail if there is no route available. * In that case we just drop the packet. * * --Lennert, 20020411 * --Bart, 20020416 (updated) * --Bart, 20021007 (updated) */ static int br_nf_pre_routing_finish_bridge(struct sk_buff *skb) { #ifdef CONFIG_NETFILTER_DEBUG skb->nf_debug |= (1 << NF_BR_PRE_ROUTING) | (1 << NF_BR_FORWARD); #endif if (skb->pkt_type == PACKET_OTHERHOST) { skb->pkt_type = PACKET_HOST; skb->nf_bridge->mask |= BRNF_PKT_TYPE; } skb->dev = bridge_parent(skb->dev); skb->dst->output(skb); return 0; } static int br_nf_pre_routing_finish(struct sk_buff *skb) { struct net_device *dev = skb->dev; struct iphdr *iph = skb->nh.iph; struct nf_bridge_info *nf_bridge = skb->nf_bridge; #ifdef CONFIG_NETFILTER_DEBUG skb->nf_debug ^= (1 << NF_BR_PRE_ROUTING); #endif if (nf_bridge->mask & BRNF_PKT_TYPE) { skb->pkt_type = PACKET_OTHERHOST; nf_bridge->mask ^= BRNF_PKT_TYPE; } if (dnat_took_place(skb)) { if (ip_route_input(skb, iph->daddr, iph->saddr, iph->tos, dev)) { struct rtable *rt; if (!ip_route_output(&rt, iph->daddr, 0, iph->tos, 0)) { /* Bridged-and-DNAT'ed traffic doesn't * require ip_forwarding. */ if (((struct dst_entry *)rt)->dev == dev) { skb->dst = (struct dst_entry *)rt; goto bridged_dnat; } __br_dnat_complain(); dst_release((struct dst_entry *)rt); } kfree_skb(skb); return 0; } else { if (skb->dst->dev == dev) { bridged_dnat: /* Tell br_nf_local_out this is a * bridged frame */ nf_bridge->mask |= BRNF_BRIDGED_DNAT; skb->dev = nf_bridge->physindev; clear_cb(skb); NF_HOOK_THRESH(PF_BRIDGE, NF_BR_PRE_ROUTING, skb, skb->dev, NULL, br_nf_pre_routing_finish_bridge, 1); return 0; } memcpy(skb->mac.ethernet->h_dest, dev->dev_addr, ETH_ALEN); } } else { skb->dst = (struct dst_entry *)&__fake_rtable; dst_hold(skb->dst); } clear_cb(skb); skb->dev = nf_bridge->physindev; NF_HOOK_THRESH(PF_BRIDGE, NF_BR_PRE_ROUTING, skb, skb->dev, NULL, br_handle_frame_finish, 1); return 0; } /* Replicate the checks that IPv4 does on packet reception. * Set skb->dev to the bridge device (i.e. parent of the * receiving device) to make netfilter happy, the REDIRECT * target in particular. Save the original destination IP * address to be able to detect DNAT afterwards. */ static unsigned int br_nf_pre_routing(unsigned int hook, struct sk_buff **pskb, const struct net_device *in, const struct net_device *out, int (*okfn)(struct sk_buff *)) { struct iphdr *iph; __u32 len; struct sk_buff *skb; struct nf_bridge_info *nf_bridge; if ((*pskb)->protocol != __constant_htons(ETH_P_IP)) return NF_ACCEPT; if ((skb = skb_share_check(*pskb, GFP_ATOMIC)) == NULL) goto out; if (!pskb_may_pull(skb, sizeof(struct iphdr))) goto inhdr_error; iph = skb->nh.iph; if (iph->ihl < 5 || iph->version != 4) goto inhdr_error; if (!pskb_may_pull(skb, 4*iph->ihl)) goto inhdr_error; iph = skb->nh.iph; if (ip_fast_csum((__u8 *)iph, iph->ihl) != 0) goto inhdr_error; len = ntohs(iph->tot_len); if (skb->len < len || len < 4*iph->ihl) goto inhdr_error; if (skb->len > len) { __pskb_trim(skb, len); if (skb->ip_summed == CHECKSUM_HW) skb->ip_summed = CHECKSUM_NONE; } #ifdef CONFIG_NETFILTER_DEBUG skb->nf_debug ^= (1 << NF_IP_PRE_ROUTING); #endif if ((nf_bridge = nf_bridge_alloc(skb)) == NULL) return NF_DROP; if (skb->pkt_type == PACKET_OTHERHOST) { skb->pkt_type = PACKET_HOST; nf_bridge->mask |= BRNF_PKT_TYPE; } nf_bridge->physindev = skb->dev; skb->dev = bridge_parent(skb->dev); store_orig_dstaddr(skb); NF_HOOK(PF_INET, NF_IP_PRE_ROUTING, skb, skb->dev, NULL, br_nf_pre_routing_finish); return NF_STOLEN; inhdr_error: // IP_INC_STATS_BH(IpInHdrErrors); out: return NF_DROP; } /* PF_BRIDGE/LOCAL_IN ************************************************/ /* The packet is locally destined, which requires a real * dst_entry, so detach the fake one. On the way up, the * packet would pass through PRE_ROUTING again (which already * took place when the packet entered the bridge), but we * register an IPv4 PRE_ROUTING 'sabotage' hook that will * prevent this from happening. */ static unsigned int br_nf_local_in(unsigned int hook, struct sk_buff **pskb, const struct net_device *in, const struct net_device *out, int (*okfn)(struct sk_buff *)) { struct sk_buff *skb = *pskb; if (skb->protocol != __constant_htons(ETH_P_IP)) return NF_ACCEPT; if (skb->dst == (struct dst_entry *)&__fake_rtable) { dst_release(skb->dst); skb->dst = NULL; } return NF_ACCEPT; } /* PF_BRIDGE/FORWARD *************************************************/ static int br_nf_forward_finish(struct sk_buff *skb) { struct nf_bridge_info *nf_bridge = skb->nf_bridge; #ifdef CONFIG_NETFILTER_DEBUG skb->nf_debug ^= (1 << NF_BR_FORWARD); #endif if (nf_bridge->mask & BRNF_PKT_TYPE) { skb->pkt_type = PACKET_OTHERHOST; nf_bridge->mask ^= BRNF_PKT_TYPE; } NF_HOOK_THRESH(PF_BRIDGE, NF_BR_FORWARD, skb, nf_bridge->physindev, skb->dev, br_forward_finish, 1); return 0; } /* This is the 'purely bridged' case. We pass the packet to * netfilter with indev and outdev set to the bridge device, * but we are still able to filter on the 'real' indev/outdev * because another bit of the bridge-nf patch overloads the * '-i' and '-o' iptables interface checks to take * skb->phys{in,out}dev into account as well (so both the real * device and the bridge device will match). */ static unsigned int br_nf_forward(unsigned int hook, struct sk_buff **pskb, const struct net_device *in, const struct net_device *out, int (*okfn)(struct sk_buff *)) { struct sk_buff *skb = *pskb; struct nf_bridge_info *nf_bridge; if (skb->protocol != __constant_htons(ETH_P_IP)) return NF_ACCEPT; #ifdef CONFIG_NETFILTER_DEBUG skb->nf_debug ^= (1 << NF_BR_FORWARD); #endif nf_bridge = skb->nf_bridge; if (skb->pkt_type == PACKET_OTHERHOST) { skb->pkt_type = PACKET_HOST; nf_bridge->mask |= BRNF_PKT_TYPE; } nf_bridge->physoutdev = skb->dev; NF_HOOK(PF_INET, NF_IP_FORWARD, skb, bridge_parent(nf_bridge->physindev), bridge_parent(skb->dev), br_nf_forward_finish); return NF_STOLEN; } /* PF_BRIDGE/LOCAL_OUT ***********************************************/ static int br_nf_local_out_finish(struct sk_buff *skb) { #ifdef CONFIG_NETFILTER_DEBUG skb->nf_debug &= ~(1 << NF_BR_LOCAL_OUT); #endif NF_HOOK_THRESH(PF_BRIDGE, NF_BR_LOCAL_OUT, skb, NULL, skb->dev, br_forward_finish, NF_BR_PRI_FIRST + 1); return 0; } /* This function sees both locally originated IP packets and forwarded * IP packets (in both cases the destination device is a bridge * device). It also sees bridged-and-DNAT'ed packets. * For the sake of interface transparency (i.e. properly * overloading the '-o' option), we steal packets destined to * a bridge device away from the PF_INET/FORWARD and PF_INET/OUTPUT hook * functions, and give them back later, when we have determined the real * output device. This is done in here. * * If (nf_bridge->mask & BRNF_BRIDGED_DNAT) then the packet is bridged * and we fake the PF_BRIDGE/FORWARD hook. The function br_nf_forward() * will then fake the PF_INET/FORWARD hook. br_nf_local_out() has priority * NF_BR_PRI_FIRST, so no relevant PF_BRIDGE/INPUT functions have been nor * will be executed. * Otherwise, if nf_bridge->physindev is NULL, the bridge-nf code never touched * this packet before, and so the packet was locally originated. We fake * the PF_INET/LOCAL_OUT hook. * Finally, if nf_bridge->physindev isn't NULL, then the packet was IP routed, * so we fake the PF_INET/FORWARD hook. ipv4_sabotage_out() makes sure * even routed packets that didn't arrive on a bridge interface have their * nf_bridge->physindev set. */ static unsigned int br_nf_local_out(unsigned int hook, struct sk_buff **pskb, const struct net_device *in, const struct net_device *out, int (*_okfn)(struct sk_buff *)) { int (*okfn)(struct sk_buff *skb); struct net_device *realindev; struct sk_buff *skb = *pskb; struct nf_bridge_info *nf_bridge; if (skb->protocol != __constant_htons(ETH_P_IP)) return NF_ACCEPT; /* Sometimes we get packets with NULL ->dst here (for example, * running a dhcp client daemon triggers this). */ if (skb->dst == NULL) return NF_ACCEPT; nf_bridge = skb->nf_bridge; nf_bridge->physoutdev = skb->dev; realindev = nf_bridge->physindev; /* Bridged, take PF_BRIDGE/FORWARD. * (see big note in front of br_nf_pre_routing_finish) */ if (nf_bridge->mask & BRNF_BRIDGED_DNAT) { okfn = br_forward_finish; if (nf_bridge->mask & BRNF_PKT_TYPE) { skb->pkt_type = PACKET_OTHERHOST; nf_bridge->mask ^= BRNF_PKT_TYPE; } NF_HOOK(PF_BRIDGE, NF_BR_FORWARD, skb, realindev, skb->dev, okfn); } else { okfn = br_nf_local_out_finish; /* IP forwarded traffic has a physindev, locally * generated traffic hasn't. */ if (realindev != NULL) { if (((nf_bridge->mask & BRNF_DONT_TAKE_PARENT) == 0) && has_bridge_parent(realindev)) realindev = bridge_parent(realindev); NF_HOOK_THRESH(PF_INET, NF_IP_FORWARD, skb, realindev, bridge_parent(skb->dev), okfn, NF_IP_PRI_BRIDGE_SABOTAGE_FORWARD + 1); } else { #ifdef CONFIG_NETFILTER_DEBUG skb->nf_debug ^= (1 << NF_IP_LOCAL_OUT); #endif NF_HOOK_THRESH(PF_INET, NF_IP_LOCAL_OUT, skb, realindev, bridge_parent(skb->dev), okfn, NF_IP_PRI_BRIDGE_SABOTAGE_LOCAL_OUT + 1); } } return NF_STOLEN; } /* PF_BRIDGE/POST_ROUTING ********************************************/ static unsigned int br_nf_post_routing(unsigned int hook, struct sk_buff **pskb, const struct net_device *in, const struct net_device *out, int (*okfn)(struct sk_buff *)) { struct sk_buff *skb = *pskb; struct nf_bridge_info *nf_bridge = (*pskb)->nf_bridge; /* Be very paranoid. */ if (skb->mac.raw < skb->head || skb->mac.raw + ETH_HLEN > skb->data) { printk(KERN_CRIT "br_netfilter: Argh!! br_nf_post_routing: " "bad mac.raw pointer."); if (skb->dev != NULL) { printk("[%s]", skb->dev->name); if (has_bridge_parent(skb->dev)) printk("[%s]", bridge_parent(skb->dev)->name); } printk("\n"); return NF_ACCEPT; } if (skb->protocol != __constant_htons(ETH_P_IP)) return NF_ACCEPT; /* Sometimes we get packets with NULL ->dst here (for example, * running a dhcp client daemon triggers this). */ if (skb->dst == NULL) return NF_ACCEPT; #ifdef CONFIG_NETFILTER_DEBUG skb->nf_debug ^= (1 << NF_IP_POST_ROUTING); #endif /* We assume any code from br_dev_queue_push_xmit onwards doesn't care * about the value of skb->pkt_type. */ if (skb->pkt_type == PACKET_OTHERHOST) { skb->pkt_type = PACKET_HOST; nf_bridge->mask |= BRNF_PKT_TYPE; } memcpy(nf_bridge->hh, skb->data - 16, 16); NF_HOOK(PF_INET, NF_IP_POST_ROUTING, skb, NULL, bridge_parent(skb->dev), br_dev_queue_push_xmit); return NF_STOLEN; } /* IPv4/SABOTAGE *****************************************************/ /* Don't hand locally destined packets to PF_INET/PRE_ROUTING * for the second time. */ static unsigned int ipv4_sabotage_in(unsigned int hook, struct sk_buff **pskb, const struct net_device *in, const struct net_device *out, int (*okfn)(struct sk_buff *)) { if (in->hard_start_xmit == br_dev_xmit && okfn != br_nf_pre_routing_finish) { okfn(*pskb); return NF_STOLEN; } return NF_ACCEPT; } /* Postpone execution of PF_INET/FORWARD, PF_INET/LOCAL_OUT * and PF_INET/POST_ROUTING until we have done the forwarding * decision in the bridge code and have determined skb->physoutdev. */ static unsigned int ipv4_sabotage_out(unsigned int hook, struct sk_buff **pskb, const struct net_device *in, const struct net_device *out, int (*okfn)(struct sk_buff *)) { if (out->hard_start_xmit == br_dev_xmit && okfn != br_nf_forward_finish && okfn != br_nf_local_out_finish && okfn != br_dev_queue_push_xmit) { struct sk_buff *skb = *pskb; struct nf_bridge_info *nf_bridge; if (!skb->nf_bridge && !nf_bridge_alloc(skb)) return NF_DROP; nf_bridge = skb->nf_bridge; /* This frame will arrive on PF_BRIDGE/LOCAL_OUT and we * will need the indev then. For a brouter, the real indev * can be a bridge port, so we make sure br_nf_local_out() * doesn't use the bridge parent of the indev by using * the BRNF_DONT_TAKE_PARENT mask. */ if (hook == NF_IP_FORWARD && nf_bridge->physindev == NULL) { nf_bridge->mask &= BRNF_DONT_TAKE_PARENT; nf_bridge->physindev = (struct net_device *)in; } okfn(skb); return NF_STOLEN; } return NF_ACCEPT; } /* For br_nf_local_out we need (prio = NF_BR_PRI_FIRST), to insure that innocent * PF_BRIDGE/NF_BR_LOCAL_OUT functions don't get bridged traffic as input. * For br_nf_post_routing, we need (prio = NF_BR_PRI_LAST), because * ip_refrag() can return NF_STOLEN. */ static struct nf_hook_ops br_nf_ops[] = { { { NULL, NULL }, br_nf_pre_routing, PF_BRIDGE, NF_BR_PRE_ROUTING, NF_BR_PRI_BRNF }, { { NULL, NULL }, br_nf_local_in, PF_BRIDGE, NF_BR_LOCAL_IN, NF_BR_PRI_BRNF }, { { NULL, NULL }, br_nf_forward, PF_BRIDGE, NF_BR_FORWARD, NF_BR_PRI_BRNF }, { { NULL, NULL }, br_nf_local_out, PF_BRIDGE, NF_BR_LOCAL_OUT, NF_BR_PRI_FIRST }, { { NULL, NULL }, br_nf_post_routing, PF_BRIDGE, NF_BR_POST_ROUTING, NF_BR_PRI_LAST }, { { NULL, NULL }, ipv4_sabotage_in, PF_INET, NF_IP_PRE_ROUTING, NF_IP_PRI_FIRST }, { { NULL, NULL }, ipv4_sabotage_out, PF_INET, NF_IP_FORWARD, NF_IP_PRI_BRIDGE_SABOTAGE_FORWARD }, { { NULL, NULL }, ipv4_sabotage_out, PF_INET, NF_IP_LOCAL_OUT, NF_IP_PRI_BRIDGE_SABOTAGE_LOCAL_OUT }, { { NULL, NULL }, ipv4_sabotage_out, PF_INET, NF_IP_POST_ROUTING, NF_IP_PRI_FIRST } }; #define NUMHOOKS (sizeof(br_nf_ops)/sizeof(br_nf_ops[0])) int br_netfilter_init(void) { int i; for (i = 0; i < NUMHOOKS; i++) { int ret; if ((ret = nf_register_hook(&br_nf_ops[i])) >= 0) continue; while (i--) nf_unregister_hook(&br_nf_ops[i]); return ret; } printk(KERN_NOTICE "Bridge firewalling registered\n"); return 0; } void br_netfilter_fini(void) { int i; for (i = NUMHOOKS - 1; i >= 0; i--) nf_unregister_hook(&br_nf_ops[i]); }