netfilter: bridge: prevent UAF in brnf_exit_net()

[mirror_ubuntu-bionic-kernel.git] / net / bridge / br_netfilter_hooks.c

/*
 *      Handle firewalling
 *      Linux ethernet bridge
 *
 *      Authors:
 *      Lennert Buytenhek               <buytenh@gnu.org>
 *      Bart De Schuymer                <bdschuym@pandora.be>
 *
 *      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 <linux/module.h>
#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/ip.h>
#include <linux/netdevice.h>
#include <linux/skbuff.h>
#include <linux/if_arp.h>
#include <linux/if_ether.h>
#include <linux/if_vlan.h>
#include <linux/if_pppox.h>
#include <linux/ppp_defs.h>
#include <linux/netfilter_bridge.h>
#include <linux/netfilter_ipv4.h>
#include <linux/netfilter_ipv6.h>
#include <linux/netfilter_arp.h>
#include <linux/in_route.h>
#include <linux/rculist.h>
#include <linux/inetdevice.h>

#include <net/ip.h>
#include <net/ipv6.h>
#include <net/addrconf.h>
#include <net/route.h>
#include <net/netfilter/br_netfilter.h>
#include <net/netns/generic.h>

#include <linux/uaccess.h>
#include "br_private.h"
#ifdef CONFIG_SYSCTL
#include <linux/sysctl.h>
#endif

static unsigned int brnf_net_id __read_mostly;

struct brnf_net {
        bool enabled;

#ifdef CONFIG_SYSCTL
        struct ctl_table_header *ctl_hdr;
#endif

        /* default value is 1 */
        int call_iptables;
        int call_ip6tables;
        int call_arptables;

        /* default value is 0 */
        int filter_vlan_tagged;
        int filter_pppoe_tagged;
        int pass_vlan_indev;
};

#define IS_IP(skb) \
        (!skb_vlan_tag_present(skb) && skb->protocol == htons(ETH_P_IP))

#define IS_IPV6(skb) \
        (!skb_vlan_tag_present(skb) && skb->protocol == htons(ETH_P_IPV6))

#define IS_ARP(skb) \
        (!skb_vlan_tag_present(skb) && skb->protocol == htons(ETH_P_ARP))

static inline __be16 vlan_proto(const struct sk_buff *skb)
{
        if (skb_vlan_tag_present(skb))
                return skb->protocol;
        else if (skb->protocol == htons(ETH_P_8021Q))
                return vlan_eth_hdr(skb)->h_vlan_encapsulated_proto;
        else
                return 0;
}

static inline bool is_vlan_ip(const struct sk_buff *skb, const struct net *net)
{
        struct brnf_net *brnet = net_generic(net, brnf_net_id);

        return vlan_proto(skb) == htons(ETH_P_IP) && brnet->filter_vlan_tagged;
}

static inline bool is_vlan_ipv6(const struct sk_buff *skb,
                                const struct net *net)
{
        struct brnf_net *brnet = net_generic(net, brnf_net_id);

        return vlan_proto(skb) == htons(ETH_P_IPV6) &&
               brnet->filter_vlan_tagged;
}

static inline bool is_vlan_arp(const struct sk_buff *skb, const struct net *net)
{
        struct brnf_net *brnet = net_generic(net, brnf_net_id);

        return vlan_proto(skb) == htons(ETH_P_ARP) && brnet->filter_vlan_tagged;
}

static inline __be16 pppoe_proto(const struct sk_buff *skb)
{
        return *((__be16 *)(skb_mac_header(skb) + ETH_HLEN +
                            sizeof(struct pppoe_hdr)));
}

static inline bool is_pppoe_ip(const struct sk_buff *skb, const struct net *net)
{
        struct brnf_net *brnet = net_generic(net, brnf_net_id);

        return skb->protocol == htons(ETH_P_PPP_SES) &&
               pppoe_proto(skb) == htons(PPP_IP) && brnet->filter_pppoe_tagged;
}

static inline bool is_pppoe_ipv6(const struct sk_buff *skb,
                                 const struct net *net)
{
        struct brnf_net *brnet = net_generic(net, brnf_net_id);

        return skb->protocol == htons(ETH_P_PPP_SES) &&
               pppoe_proto(skb) == htons(PPP_IPV6) &&
               brnet->filter_pppoe_tagged;
}

/* largest possible L2 header, see br_nf_dev_queue_xmit() */
#define NF_BRIDGE_MAX_MAC_HEADER_LENGTH (PPPOE_SES_HLEN + ETH_HLEN)

struct brnf_frag_data {
        char mac[NF_BRIDGE_MAX_MAC_HEADER_LENGTH];
        u8 encap_size;
        u8 size;
        u16 vlan_tci;
        __be16 vlan_proto;
};

static DEFINE_PER_CPU(struct brnf_frag_data, brnf_frag_data_storage);

static void nf_bridge_info_free(struct sk_buff *skb)
{
        if (skb->nf_bridge) {
                nf_bridge_put(skb->nf_bridge);
                skb->nf_bridge = NULL;
        }
}

static inline struct net_device *bridge_parent(const struct net_device *dev)
{
        struct net_bridge_port *port;

        port = br_port_get_rcu(dev);
        return port ? port->br->dev : NULL;
}

static inline struct nf_bridge_info *nf_bridge_unshare(struct sk_buff *skb)
{
        struct nf_bridge_info *nf_bridge = skb->nf_bridge;

        if (refcount_read(&nf_bridge->use) > 1) {
                struct nf_bridge_info *tmp = nf_bridge_alloc(skb);

                if (tmp) {
                        memcpy(tmp, nf_bridge, sizeof(struct nf_bridge_info));
                        refcount_set(&tmp->use, 1);
                }
                nf_bridge_put(nf_bridge);
                nf_bridge = tmp;
        }
        return nf_bridge;
}

unsigned int nf_bridge_encap_header_len(const struct sk_buff *skb)
{
        switch (skb->protocol) {
        case __cpu_to_be16(ETH_P_8021Q):
                return VLAN_HLEN;
        case __cpu_to_be16(ETH_P_PPP_SES):
                return PPPOE_SES_HLEN;
        default:
                return 0;
        }
}

static inline void nf_bridge_pull_encap_header(struct sk_buff *skb)
{
        unsigned int len = nf_bridge_encap_header_len(skb);

        skb_pull(skb, len);
        skb->network_header += len;
}

static inline void nf_bridge_pull_encap_header_rcsum(struct sk_buff *skb)
{
        unsigned int len = nf_bridge_encap_header_len(skb);

        skb_pull_rcsum(skb, len);
        skb->network_header += len;
}

/* When handing a packet over to the IP layer
 * check whether we have a skb that is in the
 * expected format
 */

static int br_validate_ipv4(struct net *net, struct sk_buff *skb)
{
        const struct iphdr *iph;
        u32 len;

        if (!pskb_may_pull(skb, sizeof(struct iphdr)))
                goto inhdr_error;

        iph = ip_hdr(skb);

        /* Basic sanity checks */
        if (iph->ihl < 5 || iph->version != 4)
                goto inhdr_error;

        if (!pskb_may_pull(skb, iph->ihl*4))
                goto inhdr_error;

        iph = ip_hdr(skb);
        if (unlikely(ip_fast_csum((u8 *)iph, iph->ihl)))
                goto inhdr_error;

        len = ntohs(iph->tot_len);
        if (skb->len < len) {
                __IP_INC_STATS(net, IPSTATS_MIB_INTRUNCATEDPKTS);
                goto drop;
        } else if (len < (iph->ihl*4))
                goto inhdr_error;

        if (pskb_trim_rcsum(skb, len)) {
                __IP_INC_STATS(net, IPSTATS_MIB_INDISCARDS);
                goto drop;
        }

        memset(IPCB(skb), 0, sizeof(struct inet_skb_parm));
        /* We should really parse IP options here but until
         * somebody who actually uses IP options complains to
         * us we'll just silently ignore the options because
         * we're lazy!
         */
        return 0;

inhdr_error:
        __IP_INC_STATS(net, IPSTATS_MIB_INHDRERRORS);
drop:
        return -1;
}

void nf_bridge_update_protocol(struct sk_buff *skb)
{
        switch (skb->nf_bridge->orig_proto) {
        case BRNF_PROTO_8021Q:
                skb->protocol = htons(ETH_P_8021Q);
                break;
        case BRNF_PROTO_PPPOE:
                skb->protocol = htons(ETH_P_PPP_SES);
                break;
        case BRNF_PROTO_UNCHANGED:
                break;
        }
}

/* Obtain the correct destination MAC address, while preserving the original
 * source MAC address. If we already know this address, we just copy it. If we
 * don't, we use the neighbour framework to find out. In both cases, we make
 * sure that br_handle_frame_finish() is called afterwards.
 */
int br_nf_pre_routing_finish_bridge(struct net *net, struct sock *sk, struct sk_buff *skb)
{
        struct neighbour *neigh;
        struct dst_entry *dst;

        skb->dev = bridge_parent(skb->dev);
        if (!skb->dev)
                goto free_skb;
        dst = skb_dst(skb);
        neigh = dst_neigh_lookup_skb(dst, skb);
        if (neigh) {
                struct nf_bridge_info *nf_bridge = nf_bridge_info_get(skb);
                int ret;

                if ((neigh->nud_state & NUD_CONNECTED) && neigh->hh.hh_len) {
                        neigh_hh_bridge(&neigh->hh, skb);
                        skb->dev = nf_bridge->physindev;
                        ret = br_handle_frame_finish(net, sk, skb);
                } else {
                        /* the neighbour function below overwrites the complete
                         * MAC header, so we save the Ethernet source address and
                         * protocol number.
                         */
                        skb_copy_from_linear_data_offset(skb,
                                                         -(ETH_HLEN-ETH_ALEN),
                                                         nf_bridge->neigh_header,
                                                         ETH_HLEN-ETH_ALEN);
                        /* tell br_dev_xmit to continue with forwarding */
                        nf_bridge->bridged_dnat = 1;
                        /* FIXME Need to refragment */
                        ret = neigh->output(neigh, skb);
                }
                neigh_release(neigh);
                return ret;
        }
free_skb:
        kfree_skb(skb);
        return 0;
}

static inline bool
br_nf_ipv4_daddr_was_changed(const struct sk_buff *skb,
                             const struct nf_bridge_info *nf_bridge)
{
        return ip_hdr(skb)->daddr != nf_bridge->ipv4_daddr;
}

/* This requires some explaining. If DNAT has taken place,
 * we will need to fix up the destination Ethernet address.
 * This is also true when SNAT takes place (for the reply direction).
 *
 * 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's first consider the case that ip_route_input() succeeds:
 *
 * If the output device equals the logical bridge device the packet
 * came in on, we can consider this bridging. The corresponding MAC
 * address will be obtained in br_nf_pre_routing_finish_bridge.
 * 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. For a redirected
 * packet, ip_route_input() will give back the localhost as output device,
 * which differs from the bridge device.
 *
 * Let's now consider the case that ip_route_input() fails:
 *
 * This can be because the destination address is martian, in which case
 * the packet will be dropped.
 * If IP forwarding is disabled, ip_route_input() will fail, while
 * ip_route_output_key() can return success. The source
 * address for ip_route_output_key() is set to zero, so ip_route_output_key()
 * thinks we're handling a locally generated packet and won't care
 * if IP forwarding is enabled. If the output device equals the logical bridge
 * device, we proceed as if ip_route_input() succeeded. If it differs from the
 * logical bridge port or if ip_route_output_key() fails we drop the packet.
 */
static int br_nf_pre_routing_finish(struct net *net, struct sock *sk, struct sk_buff *skb)
{
        struct net_device *dev = skb->dev;
        struct iphdr *iph = ip_hdr(skb);
        struct nf_bridge_info *nf_bridge = nf_bridge_info_get(skb);
        struct rtable *rt;
        int err;

        nf_bridge->frag_max_size = IPCB(skb)->frag_max_size;

        if (nf_bridge->pkt_otherhost) {
                skb->pkt_type = PACKET_OTHERHOST;
                nf_bridge->pkt_otherhost = false;
        }
        nf_bridge->in_prerouting = 0;
        if (br_nf_ipv4_daddr_was_changed(skb, nf_bridge)) {
                if ((err = ip_route_input(skb, iph->daddr, iph->saddr, iph->tos, dev))) {
                        struct in_device *in_dev = __in_dev_get_rcu(dev);

                        /* If err equals -EHOSTUNREACH the error is due to a
                         * martian destination or due to the fact that
                         * forwarding is disabled. For most martian packets,
                         * ip_route_output_key() will fail. It won't fail for 2 types of
                         * martian destinations: loopback destinations and destination
                         * 0.0.0.0. In both cases the packet will be dropped because the
                         * destination is the loopback device and not the bridge. */
                        if (err != -EHOSTUNREACH || !in_dev || IN_DEV_FORWARD(in_dev))
                                goto free_skb;

                        rt = ip_route_output(net, iph->daddr, 0,
                                             RT_TOS(iph->tos), 0);
                        if (!IS_ERR(rt)) {
                                /* - Bridged-and-DNAT'ed traffic doesn't
                                 *   require ip_forwarding. */
                                if (rt->dst.dev == dev) {
                                        skb_dst_set(skb, &rt->dst);
                                        goto bridged_dnat;
                                }
                                ip_rt_put(rt);
                        }
free_skb:
                        kfree_skb(skb);
                        return 0;
                } else {
                        if (skb_dst(skb)->dev == dev) {
bridged_dnat:
                                skb->dev = nf_bridge->physindev;
                                nf_bridge_update_protocol(skb);
                                nf_bridge_push_encap_header(skb);
                                br_nf_hook_thresh(NF_BR_PRE_ROUTING,
                                                  net, sk, skb, skb->dev,
                                                  NULL,
                                                  br_nf_pre_routing_finish_bridge);
                                return 0;
                        }
                        ether_addr_copy(eth_hdr(skb)->h_dest, dev->dev_addr);
                        skb->pkt_type = PACKET_HOST;
                }
        } else {
                rt = bridge_parent_rtable(nf_bridge->physindev);
                if (!rt) {
                        kfree_skb(skb);
                        return 0;
                }
                skb_dst_set_noref(skb, &rt->dst);
        }

        skb->dev = nf_bridge->physindev;
        nf_bridge_update_protocol(skb);
        nf_bridge_push_encap_header(skb);
        br_nf_hook_thresh(NF_BR_PRE_ROUTING, net, sk, skb, skb->dev, NULL,
                          br_handle_frame_finish);
        return 0;
}

static struct net_device *brnf_get_logical_dev(struct sk_buff *skb,
                                               const struct net_device *dev,
                                               const struct net *net)
{
        struct net_device *vlan, *br;
        struct brnf_net *brnet = net_generic(net, brnf_net_id);

        br = bridge_parent(dev);

        if (brnet->pass_vlan_indev == 0 || !skb_vlan_tag_present(skb))
                return br;

        vlan = __vlan_find_dev_deep_rcu(br, skb->vlan_proto,
                                    skb_vlan_tag_get(skb) & VLAN_VID_MASK);

        return vlan ? vlan : br;
}

/* Some common code for IPv4/IPv6 */
struct net_device *setup_pre_routing(struct sk_buff *skb, const struct net *net)
{
        struct nf_bridge_info *nf_bridge = nf_bridge_info_get(skb);

        if (skb->pkt_type == PACKET_OTHERHOST) {
                skb->pkt_type = PACKET_HOST;
                nf_bridge->pkt_otherhost = true;
        }

        nf_bridge->in_prerouting = 1;
        nf_bridge->physindev = skb->dev;
        skb->dev = brnf_get_logical_dev(skb, skb->dev, net);

        if (skb->protocol == htons(ETH_P_8021Q))
                nf_bridge->orig_proto = BRNF_PROTO_8021Q;
        else if (skb->protocol == htons(ETH_P_PPP_SES))
                nf_bridge->orig_proto = BRNF_PROTO_PPPOE;

        /* Must drop socket now because of tproxy. */
        skb_orphan(skb);
        return skb->dev;
}

/* Direct IPv6 traffic to br_nf_pre_routing_ipv6.
 * 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(void *priv,
                                      struct sk_buff *skb,
                                      const struct nf_hook_state *state)
{
        struct nf_bridge_info *nf_bridge;
        struct net_bridge_port *p;
        struct net_bridge *br;
        __u32 len = nf_bridge_encap_header_len(skb);
        struct brnf_net *brnet;

        if (unlikely(!pskb_may_pull(skb, len)))
                return NF_DROP;

        p = br_port_get_rcu(state->in);
        if (p == NULL)
                return NF_DROP;
        br = p->br;

        brnet = net_generic(state->net, brnf_net_id);
        if (IS_IPV6(skb) || is_vlan_ipv6(skb, state->net) ||
            is_pppoe_ipv6(skb, state->net)) {
                if (!brnet->call_ip6tables &&
                    !br_opt_get(br, BROPT_NF_CALL_IP6TABLES))
                        return NF_ACCEPT;

                nf_bridge_pull_encap_header_rcsum(skb);
                return br_nf_pre_routing_ipv6(priv, skb, state);
        }

        if (!brnet->call_iptables && !br_opt_get(br, BROPT_NF_CALL_IPTABLES))
                return NF_ACCEPT;

        if (!IS_IP(skb) && !is_vlan_ip(skb, state->net) &&
            !is_pppoe_ip(skb, state->net))
                return NF_ACCEPT;

        nf_bridge_pull_encap_header_rcsum(skb);

        if (br_validate_ipv4(state->net, skb))
                return NF_DROP;

        nf_bridge_put(skb->nf_bridge);
        if (!nf_bridge_alloc(skb))
                return NF_DROP;
        if (!setup_pre_routing(skb, state->net))
                return NF_DROP;

        nf_bridge = nf_bridge_info_get(skb);
        nf_bridge->ipv4_daddr = ip_hdr(skb)->daddr;

        skb->protocol = htons(ETH_P_IP);
        skb->transport_header = skb->network_header + ip_hdr(skb)->ihl * 4;

        NF_HOOK(NFPROTO_IPV4, NF_INET_PRE_ROUTING, state->net, state->sk, skb,
                skb->dev, NULL,
                br_nf_pre_routing_finish);

        return NF_STOLEN;
}


/* PF_BRIDGE/FORWARD *************************************************/
static int br_nf_forward_finish(struct net *net, struct sock *sk, struct sk_buff *skb)
{
        struct nf_bridge_info *nf_bridge = nf_bridge_info_get(skb);
        struct net_device *in;

        if (!IS_ARP(skb) && !is_vlan_arp(skb, net)) {

                if (skb->protocol == htons(ETH_P_IP))
                        nf_bridge->frag_max_size = IPCB(skb)->frag_max_size;

                if (skb->protocol == htons(ETH_P_IPV6))
                        nf_bridge->frag_max_size = IP6CB(skb)->frag_max_size;

                in = nf_bridge->physindev;
                if (nf_bridge->pkt_otherhost) {
                        skb->pkt_type = PACKET_OTHERHOST;
                        nf_bridge->pkt_otherhost = false;
                }
                nf_bridge_update_protocol(skb);
        } else {
                in = *((struct net_device **)(skb->cb));
        }
        nf_bridge_push_encap_header(skb);

        br_nf_hook_thresh(NF_BR_FORWARD, net, sk, skb, in, skb->dev,
                          br_forward_finish);
        return 0;
}


/* This is the 'purely bridged' case.  For IP, 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 of the physdev module. For ARP, indev and outdev are the
 * bridge ports. */
static unsigned int br_nf_forward_ip(void *priv,
                                     struct sk_buff *skb,
                                     const struct nf_hook_state *state)
{
        struct nf_bridge_info *nf_bridge;
        struct net_device *parent;
        u_int8_t pf;

        if (!skb->nf_bridge)
                return NF_ACCEPT;

        /* Need exclusive nf_bridge_info since we might have multiple
         * different physoutdevs. */
        if (!nf_bridge_unshare(skb))
                return NF_DROP;

        nf_bridge = nf_bridge_info_get(skb);
        if (!nf_bridge)
                return NF_DROP;

        parent = bridge_parent(state->out);
        if (!parent)
                return NF_DROP;

        if (IS_IP(skb) || is_vlan_ip(skb, state->net) ||
            is_pppoe_ip(skb, state->net))
                pf = NFPROTO_IPV4;
        else if (IS_IPV6(skb) || is_vlan_ipv6(skb, state->net) ||
                 is_pppoe_ipv6(skb, state->net))
                pf = NFPROTO_IPV6;
        else
                return NF_ACCEPT;

        nf_bridge_pull_encap_header(skb);

        if (skb->pkt_type == PACKET_OTHERHOST) {
                skb->pkt_type = PACKET_HOST;
                nf_bridge->pkt_otherhost = true;
        }

        if (pf == NFPROTO_IPV4) {
                if (br_validate_ipv4(state->net, skb))
                        return NF_DROP;
                IPCB(skb)->frag_max_size = nf_bridge->frag_max_size;
        }

        if (pf == NFPROTO_IPV6) {
                if (br_validate_ipv6(state->net, skb))
                        return NF_DROP;
                IP6CB(skb)->frag_max_size = nf_bridge->frag_max_size;
        }

        nf_bridge->physoutdev = skb->dev;
        if (pf == NFPROTO_IPV4)
                skb->protocol = htons(ETH_P_IP);
        else
                skb->protocol = htons(ETH_P_IPV6);

        NF_HOOK(pf, NF_INET_FORWARD, state->net, NULL, skb,
                brnf_get_logical_dev(skb, state->in, state->net),
                parent, br_nf_forward_finish);

        return NF_STOLEN;
}

static unsigned int br_nf_forward_arp(void *priv,
                                      struct sk_buff *skb,
                                      const struct nf_hook_state *state)
{
        struct net_bridge_port *p;
        struct net_bridge *br;
        struct net_device **d = (struct net_device **)(skb->cb);
        struct brnf_net *brnet;

        p = br_port_get_rcu(state->out);
        if (p == NULL)
                return NF_ACCEPT;
        br = p->br;

        brnet = net_generic(state->net, brnf_net_id);
        if (!brnet->call_arptables && !br_opt_get(br, BROPT_NF_CALL_ARPTABLES))
                return NF_ACCEPT;

        if (!IS_ARP(skb)) {
                if (!is_vlan_arp(skb, state->net))
                        return NF_ACCEPT;
                nf_bridge_pull_encap_header(skb);
        }

        if (arp_hdr(skb)->ar_pln != 4) {
                if (is_vlan_arp(skb, state->net))
                        nf_bridge_push_encap_header(skb);
                return NF_ACCEPT;
        }
        *d = state->in;
        NF_HOOK(NFPROTO_ARP, NF_ARP_FORWARD, state->net, state->sk, skb,
                state->in, state->out, br_nf_forward_finish);

        return NF_STOLEN;
}

static int br_nf_push_frag_xmit(struct net *net, struct sock *sk, struct sk_buff *skb)
{
        struct brnf_frag_data *data;
        int err;

        data = this_cpu_ptr(&brnf_frag_data_storage);
        err = skb_cow_head(skb, data->size);

        if (err) {
                kfree_skb(skb);
                return 0;
        }

        if (data->vlan_tci) {
                skb->vlan_tci = data->vlan_tci;
                skb->vlan_proto = data->vlan_proto;
        }

        skb_copy_to_linear_data_offset(skb, -data->size, data->mac, data->size);
        __skb_push(skb, data->encap_size);

        nf_bridge_info_free(skb);
        return br_dev_queue_push_xmit(net, sk, skb);
}

static int
br_nf_ip_fragment(struct net *net, struct sock *sk, struct sk_buff *skb,
                  int (*output)(struct net *, struct sock *, struct sk_buff *))
{
        unsigned int mtu = ip_skb_dst_mtu(sk, skb);
        struct iphdr *iph = ip_hdr(skb);

        if (unlikely(((iph->frag_off & htons(IP_DF)) && !skb->ignore_df) ||
                     (IPCB(skb)->frag_max_size &&
                      IPCB(skb)->frag_max_size > mtu))) {
                IP_INC_STATS(net, IPSTATS_MIB_FRAGFAILS);
                kfree_skb(skb);
                return -EMSGSIZE;
        }

        return ip_do_fragment(net, sk, skb, output);
}

static unsigned int nf_bridge_mtu_reduction(const struct sk_buff *skb)
{
        if (skb->nf_bridge->orig_proto == BRNF_PROTO_PPPOE)
                return PPPOE_SES_HLEN;
        return 0;
}

static int br_nf_dev_queue_xmit(struct net *net, struct sock *sk, struct sk_buff *skb)
{
        struct nf_bridge_info *nf_bridge = nf_bridge_info_get(skb);
        unsigned int mtu, mtu_reserved;

        mtu_reserved = nf_bridge_mtu_reduction(skb);
        mtu = skb->dev->mtu;

        if (nf_bridge->frag_max_size && nf_bridge->frag_max_size < mtu)
                mtu = nf_bridge->frag_max_size;

        if (skb_is_gso(skb) || skb->len + mtu_reserved <= mtu) {
                nf_bridge_info_free(skb);
                return br_dev_queue_push_xmit(net, sk, skb);
        }

        /* This is wrong! We should preserve the original fragment
         * boundaries by preserving frag_list rather than refragmenting.
         */
        if (IS_ENABLED(CONFIG_NF_DEFRAG_IPV4) &&
            skb->protocol == htons(ETH_P_IP)) {
                struct brnf_frag_data *data;

                if (br_validate_ipv4(net, skb))
                        goto drop;

                IPCB(skb)->frag_max_size = nf_bridge->frag_max_size;

                nf_bridge_update_protocol(skb);

                data = this_cpu_ptr(&brnf_frag_data_storage);

                data->vlan_tci = skb->vlan_tci;
                data->vlan_proto = skb->vlan_proto;
                data->encap_size = nf_bridge_encap_header_len(skb);
                data->size = ETH_HLEN + data->encap_size;

                skb_copy_from_linear_data_offset(skb, -data->size, data->mac,
                                                 data->size);

                return br_nf_ip_fragment(net, sk, skb, br_nf_push_frag_xmit);
        }
        if (IS_ENABLED(CONFIG_NF_DEFRAG_IPV6) &&
            skb->protocol == htons(ETH_P_IPV6)) {
                const struct nf_ipv6_ops *v6ops = nf_get_ipv6_ops();
                struct brnf_frag_data *data;

                if (br_validate_ipv6(net, skb))
                        goto drop;

                IP6CB(skb)->frag_max_size = nf_bridge->frag_max_size;

                nf_bridge_update_protocol(skb);

                data = this_cpu_ptr(&brnf_frag_data_storage);
                data->encap_size = nf_bridge_encap_header_len(skb);
                data->size = ETH_HLEN + data->encap_size;

                skb_copy_from_linear_data_offset(skb, -data->size, data->mac,
                                                 data->size);

                if (v6ops)
                        return v6ops->fragment(net, sk, skb, br_nf_push_frag_xmit);

                kfree_skb(skb);
                return -EMSGSIZE;
        }
        nf_bridge_info_free(skb);
        return br_dev_queue_push_xmit(net, sk, skb);
 drop:
        kfree_skb(skb);
        return 0;
}

/* PF_BRIDGE/POST_ROUTING ********************************************/
static unsigned int br_nf_post_routing(void *priv,
                                       struct sk_buff *skb,
                                       const struct nf_hook_state *state)
{
        struct nf_bridge_info *nf_bridge = nf_bridge_info_get(skb);
        struct net_device *realoutdev = bridge_parent(skb->dev);
        u_int8_t pf;

        /* if nf_bridge is set, but ->physoutdev is NULL, this packet came in
         * on a bridge, but was delivered locally and is now being routed:
         *
         * POST_ROUTING was already invoked from the ip stack.
         */
        if (!nf_bridge || !nf_bridge->physoutdev)
                return NF_ACCEPT;

        if (!realoutdev)
                return NF_DROP;

        if (IS_IP(skb) || is_vlan_ip(skb, state->net) ||
            is_pppoe_ip(skb, state->net))
                pf = NFPROTO_IPV4;
        else if (IS_IPV6(skb) || is_vlan_ipv6(skb, state->net) ||
                 is_pppoe_ipv6(skb, state->net))
                pf = NFPROTO_IPV6;
        else
                return NF_ACCEPT;

        /* 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->pkt_otherhost = true;
        }

        nf_bridge_pull_encap_header(skb);
        if (pf == NFPROTO_IPV4)
                skb->protocol = htons(ETH_P_IP);
        else
                skb->protocol = htons(ETH_P_IPV6);

        NF_HOOK(pf, NF_INET_POST_ROUTING, state->net, state->sk, skb,
                NULL, realoutdev,
                br_nf_dev_queue_xmit);

        return NF_STOLEN;
}

/* IP/SABOTAGE *****************************************************/
/* Don't hand locally destined packets to PF_INET(6)/PRE_ROUTING
 * for the second time. */
static unsigned int ip_sabotage_in(void *priv,
                                   struct sk_buff *skb,
                                   const struct nf_hook_state *state)
{
        if (skb->nf_bridge && !skb->nf_bridge->in_prerouting &&
            !netif_is_l3_master(skb->dev)) {
                state->okfn(state->net, state->sk, skb);
                return NF_STOLEN;
        }

        return NF_ACCEPT;
}

/* This is called when br_netfilter has called into iptables/netfilter,
 * and DNAT has taken place on a bridge-forwarded packet.
 *
 * neigh->output has created a new MAC header, with local br0 MAC
 * as saddr.
 *
 * This restores the original MAC saddr of the bridged packet
 * before invoking bridge forward logic to transmit the packet.
 */
static void br_nf_pre_routing_finish_bridge_slow(struct sk_buff *skb)
{
        struct nf_bridge_info *nf_bridge = nf_bridge_info_get(skb);

        skb_pull(skb, ETH_HLEN);
        nf_bridge->bridged_dnat = 0;

        BUILD_BUG_ON(sizeof(nf_bridge->neigh_header) != (ETH_HLEN - ETH_ALEN));

        skb_copy_to_linear_data_offset(skb, -(ETH_HLEN - ETH_ALEN),
                                       nf_bridge->neigh_header,
                                       ETH_HLEN - ETH_ALEN);
        skb->dev = nf_bridge->physindev;

        nf_bridge->physoutdev = NULL;
        br_handle_frame_finish(dev_net(skb->dev), NULL, skb);
}

static int br_nf_dev_xmit(struct sk_buff *skb)
{
        if (skb->nf_bridge && skb->nf_bridge->bridged_dnat) {
                br_nf_pre_routing_finish_bridge_slow(skb);
                return 1;
        }
        return 0;
}

static const struct nf_br_ops br_ops = {
        .br_dev_xmit_hook =     br_nf_dev_xmit,
};

/* For br_nf_post_routing, we need (prio = NF_BR_PRI_LAST), because
 * br_dev_queue_push_xmit is called afterwards */
static const struct nf_hook_ops br_nf_ops[] = {
        {
                .hook = br_nf_pre_routing,
                .pf = NFPROTO_BRIDGE,
                .hooknum = NF_BR_PRE_ROUTING,
                .priority = NF_BR_PRI_BRNF,
        },
        {
                .hook = br_nf_forward_ip,
                .pf = NFPROTO_BRIDGE,
                .hooknum = NF_BR_FORWARD,
                .priority = NF_BR_PRI_BRNF - 1,
        },
        {
                .hook = br_nf_forward_arp,
                .pf = NFPROTO_BRIDGE,
                .hooknum = NF_BR_FORWARD,
                .priority = NF_BR_PRI_BRNF,
        },
        {
                .hook = br_nf_post_routing,
                .pf = NFPROTO_BRIDGE,
                .hooknum = NF_BR_POST_ROUTING,
                .priority = NF_BR_PRI_LAST,
        },
        {
                .hook = ip_sabotage_in,
                .pf = NFPROTO_IPV4,
                .hooknum = NF_INET_PRE_ROUTING,
                .priority = NF_IP_PRI_FIRST,
        },
        {
                .hook = ip_sabotage_in,
                .pf = NFPROTO_IPV6,
                .hooknum = NF_INET_PRE_ROUTING,
                .priority = NF_IP6_PRI_FIRST,
        },
};

static int brnf_device_event(struct notifier_block *unused, unsigned long event,
                             void *ptr)
{
        struct net_device *dev = netdev_notifier_info_to_dev(ptr);
        struct brnf_net *brnet;
        struct net *net;
        int ret;

        if (event != NETDEV_REGISTER || !(dev->priv_flags & IFF_EBRIDGE))
                return NOTIFY_DONE;

        ASSERT_RTNL();

        net = dev_net(dev);
        brnet = net_generic(net, brnf_net_id);
        if (brnet->enabled)
                return NOTIFY_OK;

        ret = nf_register_net_hooks(net, br_nf_ops, ARRAY_SIZE(br_nf_ops));
        if (ret)
                return NOTIFY_BAD;

        brnet->enabled = true;
        return NOTIFY_OK;
}

static struct notifier_block brnf_notifier __read_mostly = {
        .notifier_call = brnf_device_event,
};

/* recursively invokes nf_hook_slow (again), skipping already-called
 * hooks (< NF_BR_PRI_BRNF).
 *
 * Called with rcu read lock held.
 */
int br_nf_hook_thresh(unsigned int hook, struct net *net,
                      struct sock *sk, struct sk_buff *skb,
                      struct net_device *indev,
                      struct net_device *outdev,
                      int (*okfn)(struct net *, struct sock *,
                                  struct sk_buff *))
{
        const struct nf_hook_entries *e;
        struct nf_hook_state state;
        struct nf_hook_ops **ops;
        unsigned int i;
        int ret;

        e = rcu_dereference(net->nf.hooks[NFPROTO_BRIDGE][hook]);
        if (!e)
                return okfn(net, sk, skb);

        ops = nf_hook_entries_get_hook_ops(e);
        for (i = 0; i < e->num_hook_entries &&
              ops[i]->priority <= NF_BR_PRI_BRNF; i++)
                ;

        nf_hook_state_init(&state, hook, NFPROTO_BRIDGE, indev, outdev,
                           sk, net, okfn);

        ret = nf_hook_slow(skb, &state, e, i);
        if (ret == 1)
                ret = okfn(net, sk, skb);

        return ret;
}

#ifdef CONFIG_SYSCTL
static
int brnf_sysctl_call_tables(struct ctl_table *ctl, int write,
                            void __user *buffer, size_t *lenp, loff_t *ppos)
{
        int ret;

        ret = proc_dointvec(ctl, write, buffer, lenp, ppos);

        if (write && *(int *)(ctl->data))
                *(int *)(ctl->data) = 1;
        return ret;
}

static struct ctl_table brnf_table[] = {
        {
                .procname       = "bridge-nf-call-arptables",
                .maxlen         = sizeof(int),
                .mode           = 0644,
                .proc_handler   = brnf_sysctl_call_tables,
        },
        {
                .procname       = "bridge-nf-call-iptables",
                .maxlen         = sizeof(int),
                .mode           = 0644,
                .proc_handler   = brnf_sysctl_call_tables,
        },
        {
                .procname       = "bridge-nf-call-ip6tables",
                .maxlen         = sizeof(int),
                .mode           = 0644,
                .proc_handler   = brnf_sysctl_call_tables,
        },
        {
                .procname       = "bridge-nf-filter-vlan-tagged",
                .maxlen         = sizeof(int),
                .mode           = 0644,
                .proc_handler   = brnf_sysctl_call_tables,
        },
        {
                .procname       = "bridge-nf-filter-pppoe-tagged",
                .maxlen         = sizeof(int),
                .mode           = 0644,
                .proc_handler   = brnf_sysctl_call_tables,
        },
        {
                .procname       = "bridge-nf-pass-vlan-input-dev",
                .maxlen         = sizeof(int),
                .mode           = 0644,
                .proc_handler   = brnf_sysctl_call_tables,
        },
        { }
};

static inline void br_netfilter_sysctl_default(struct brnf_net *brnf)
{
        brnf->call_iptables = 1;
        brnf->call_ip6tables = 1;
        brnf->call_arptables = 1;
        brnf->filter_vlan_tagged = 0;
        brnf->filter_pppoe_tagged = 0;
        brnf->pass_vlan_indev = 0;
}

static int br_netfilter_sysctl_init_net(struct net *net)
{
        struct ctl_table *table = brnf_table;
        struct brnf_net *brnet;

        if (!net_eq(net, &init_net)) {
                table = kmemdup(table, sizeof(brnf_table), GFP_KERNEL);
                if (!table)
                        return -ENOMEM;
        }

        brnet = net_generic(net, brnf_net_id);
        table[0].data = &brnet->call_arptables;
        table[1].data = &brnet->call_iptables;
        table[2].data = &brnet->call_ip6tables;
        table[3].data = &brnet->filter_vlan_tagged;
        table[4].data = &brnet->filter_pppoe_tagged;
        table[5].data = &brnet->pass_vlan_indev;

        br_netfilter_sysctl_default(brnet);

        brnet->ctl_hdr = register_net_sysctl(net, "net/bridge", table);
        if (!brnet->ctl_hdr) {
                if (!net_eq(net, &init_net))
                        kfree(table);

                return -ENOMEM;
        }

        return 0;
}

static void br_netfilter_sysctl_exit_net(struct net *net,
                                         struct brnf_net *brnet)
{
        struct ctl_table *table = brnet->ctl_hdr->ctl_table_arg;

        unregister_net_sysctl_table(brnet->ctl_hdr);
        if (!net_eq(net, &init_net))
                kfree(table);
}

static int __net_init brnf_init_net(struct net *net)
{
        return br_netfilter_sysctl_init_net(net);
}
#endif

static void __net_exit brnf_exit_net(struct net *net)
{
        struct brnf_net *brnet;

        brnet = net_generic(net, brnf_net_id);
        if (brnet->enabled) {
                nf_unregister_net_hooks(net, br_nf_ops, ARRAY_SIZE(br_nf_ops));
                brnet->enabled = false;
        }

#ifdef CONFIG_SYSCTL
        br_netfilter_sysctl_exit_net(net, brnet);
#endif
}

static struct pernet_operations brnf_net_ops __read_mostly = {
#ifdef CONFIG_SYSCTL
        .init = brnf_init_net,
#endif
        .exit = brnf_exit_net,
        .id   = &brnf_net_id,
        .size = sizeof(struct brnf_net),
};

static int __init br_netfilter_init(void)
{
        int ret;

        ret = register_pernet_subsys(&brnf_net_ops);
        if (ret < 0)
                return ret;

        ret = register_netdevice_notifier(&brnf_notifier);
        if (ret < 0) {
                unregister_pernet_subsys(&brnf_net_ops);
                return ret;
        }

        RCU_INIT_POINTER(nf_br_ops, &br_ops);
        printk(KERN_NOTICE "Bridge firewalling registered\n");
        return 0;
}

static void __exit br_netfilter_fini(void)
{
        RCU_INIT_POINTER(nf_br_ops, NULL);
        unregister_netdevice_notifier(&brnf_notifier);
        unregister_pernet_subsys(&brnf_net_ops);
}

module_init(br_netfilter_init);
module_exit(br_netfilter_fini);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Lennert Buytenhek <buytenh@gnu.org>");
MODULE_AUTHOR("Bart De Schuymer <bdschuym@pandora.be>");
MODULE_DESCRIPTION("Linux ethernet netfilter firewall bridge");