netfilter.c

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/* netfilter.c: look after the filters for various protocols. 
 * Heavily influenced by the old firewall.c by David Bonn and Alan Cox.
 *
 * Thanks to Rob `CmdrTaco' Malda for not influencing this code in any
 * way.
 *
 * Rusty Russell (C)2000 -- This code is GPL.
 *
 * February 2000: Modified by James Morris to have 1 queue per protocol.
 * 15-Mar-2000:   Added NF_REPEAT --RR.
 */
#include <linux/config.h>
#include <linux/netfilter.h>
#include <net/protocol.h>
#include <linux/init.h>
#include <linux/skbuff.h>
#include <linux/wait.h>
#include <linux/module.h>
#include <linux/interrupt.h>
#include <linux/if.h>
#include <linux/netdevice.h>
#include <linux/brlock.h>
#include <linux/inetdevice.h>
#include <net/sock.h>
#include <net/route.h>
#include <linux/ip.h>

#define __KERNEL_SYSCALLS__
#include <linux/unistd.h>

/* In this code, we can be waiting indefinitely for userspace to
 * service a packet if a hook returns NF_QUEUE.  We could keep a count
 * of skbuffs queued for userspace, and not deregister a hook unless
 * this is zero, but that sucks.  Now, we simply check when the
 * packets come back: if the hook is gone, the packet is discarded. */
#ifdef CONFIG_NETFILTER_DEBUG
#define NFDEBUG(format, args...)  printk(format , ## args)
#else
#define NFDEBUG(format, args...)
#endif

/* Sockopts only registered and called from user context, so
   BR_NETPROTO_LOCK would be overkill.  Also, [gs]etsockopt calls may
   sleep. */
static DECLARE_MUTEX(nf_sockopt_mutex);

struct list_head nf_hooks[NPROTO][NF_MAX_HOOKS];
static LIST_HEAD(nf_sockopts);

/* 
 * A queue handler may be registered for each protocol.  Each is protected by
 * long term mutex.  The handler must provide an an outfn() to accept packets
 * for queueing and must reinject all packets it receives, no matter what.
 */
static struct nf_queue_handler_t {
        nf_queue_outfn_t outfn;
        void *data;
} queue_handler[NPROTO];

int nf_register_hook(struct nf_hook_ops *reg)
{
        struct list_head *i;

        br_write_lock_bh(BR_NETPROTO_LOCK);
        for (i = nf_hooks[reg->pf][reg->hooknum].next; 
             i != &nf_hooks[reg->pf][reg->hooknum]; 
             i = i->next) {
                if (reg->priority < ((struct nf_hook_ops *)i)->priority)
                        break;
        }
        list_add(&reg->list, i->prev);
        br_write_unlock_bh(BR_NETPROTO_LOCK);
        return 0;
}

void nf_unregister_hook(struct nf_hook_ops *reg)
{
        br_write_lock_bh(BR_NETPROTO_LOCK);
        list_del(&reg->list);
        br_write_unlock_bh(BR_NETPROTO_LOCK);
}

/* Do exclusive ranges overlap? */
static inline int overlap(int min1, int max1, int min2, int max2)
{
        return max1 > min2 && min1 < max2;
}

/* Functions to register sockopt ranges (exclusive). */
int nf_register_sockopt(struct nf_sockopt_ops *reg)
{
        struct list_head *i;
        int ret = 0;

        if (down_interruptible(&nf_sockopt_mutex) != 0)
                return -EINTR;

        for (i = nf_sockopts.next; i != &nf_sockopts; i = i->next) {
                struct nf_sockopt_ops *ops = (struct nf_sockopt_ops *)i;
                if (ops->pf == reg->pf
                    && (overlap(ops->set_optmin, ops->set_optmax, 
                                reg->set_optmin, reg->set_optmax)
                        || overlap(ops->get_optmin, ops->get_optmax, 
                                   reg->get_optmin, reg->get_optmax))) {
                        NFDEBUG("nf_sock overlap: %u-%u/%u-%u v %u-%u/%u-%u\n",
                                ops->set_optmin, ops->set_optmax, 
                                ops->get_optmin, ops->get_optmax, 
                                reg->set_optmin, reg->set_optmax,
                                reg->get_optmin, reg->get_optmax);
                        ret = -EBUSY;
                        goto out;
                }
        }

        list_add(&reg->list, &nf_sockopts);
out:
        up(&nf_sockopt_mutex);
        return ret;
}

void nf_unregister_sockopt(struct nf_sockopt_ops *reg)
{
        /* No point being interruptible: we're probably in cleanup_module() */
 restart:
        down(&nf_sockopt_mutex);
        if (reg->use != 0) {
                /* To be woken by nf_sockopt call... */
                /* FIXME: Stuart Young's name appears gratuitously. */
                set_current_state(TASK_UNINTERRUPTIBLE);
                reg->cleanup_task = current;
                up(&nf_sockopt_mutex);
                schedule();
                goto restart;
        }
        list_del(&reg->list);
        up(&nf_sockopt_mutex);
}

#ifdef CONFIG_NETFILTER_DEBUG
#include <net/ip.h>
#include <net/route.h>
#include <net/tcp.h>
#include <linux/netfilter_ipv4.h>

static void debug_print_hooks_ip(unsigned int nf_debug)
{
        if (nf_debug & (1 << NF_IP_PRE_ROUTING)) {
                printk("PRE_ROUTING ");
                nf_debug ^= (1 << NF_IP_PRE_ROUTING);
        }
        if (nf_debug & (1 << NF_IP_LOCAL_IN)) {
                printk("LOCAL_IN ");
                nf_debug ^= (1 << NF_IP_LOCAL_IN);
        }
        if (nf_debug & (1 << NF_IP_FORWARD)) {
                printk("FORWARD ");
                nf_debug ^= (1 << NF_IP_FORWARD);
        }
        if (nf_debug & (1 << NF_IP_LOCAL_OUT)) {
                printk("LOCAL_OUT ");
                nf_debug ^= (1 << NF_IP_LOCAL_OUT);
        }
        if (nf_debug & (1 << NF_IP_POST_ROUTING)) {
                printk("POST_ROUTING ");
                nf_debug ^= (1 << NF_IP_POST_ROUTING);
        }
        if (nf_debug)
                printk("Crap bits: 0x%04X", nf_debug);
        printk("\n");
}

void nf_dump_skb(int pf, struct sk_buff *skb)
{
        printk("skb: pf=%i %s dev=%s len=%u\n", 
               pf,
               skb->sk ? "(owned)" : "(unowned)",
               skb->dev ? skb->dev->name : "(no dev)",
               skb->len);
        switch (pf) {
        case PF_INET: {
                const struct iphdr *ip = skb->nh.iph;
                __u32 *opt = (__u32 *) (ip + 1);
                int opti;
                __u16 src_port = 0, dst_port = 0;

                if (ip->protocol == IPPROTO_TCP
                    || ip->protocol == IPPROTO_UDP) {
                        struct tcphdr *tcp=(struct tcphdr *)((__u32 *)ip+ip->ihl);
                        src_port = ntohs(tcp->source);
                        dst_port = ntohs(tcp->dest);
                }
        
                printk("PROTO=%d %u.%u.%u.%u:%hu %u.%u.%u.%u:%hu"
                       " L=%hu S=0x%2.2hX I=%hu F=0x%4.4hX T=%hu",
                       ip->protocol, NIPQUAD(ip->saddr),
                       src_port, NIPQUAD(ip->daddr),
                       dst_port,
                       ntohs(ip->tot_len), ip->tos, ntohs(ip->id),
                       ntohs(ip->frag_off), ip->ttl);

                for (opti = 0; opti < (ip->ihl - sizeof(struct iphdr) / 4); opti++)
                        printk(" O=0x%8.8X", *opt++);
                printk("\n");
        }
        }
}

void nf_debug_ip_local_deliver(struct sk_buff *skb)
{
        /* If it's a loopback packet, it must have come through
         * NF_IP_LOCAL_OUT, NF_IP_RAW_INPUT, NF_IP_PRE_ROUTING and
         * NF_IP_LOCAL_IN.  Otherwise, must have gone through
         * NF_IP_RAW_INPUT and NF_IP_PRE_ROUTING.  */
        if (!skb->dev) {
                printk("ip_local_deliver: skb->dev is NULL.\n");
        }
        else if (strcmp(skb->dev->name, "lo") == 0) {
                if (skb->nf_debug != ((1 << NF_IP_LOCAL_OUT)
                                      | (1 << NF_IP_POST_ROUTING)
                                      | (1 << NF_IP_PRE_ROUTING)
                                      | (1 << NF_IP_LOCAL_IN))) {
                        printk("ip_local_deliver: bad loopback skb: ");
                        debug_print_hooks_ip(skb->nf_debug);
                        nf_dump_skb(PF_INET, skb);
                }
        }
        else {
                if (skb->nf_debug != ((1<<NF_IP_PRE_ROUTING)
                                      | (1<<NF_IP_LOCAL_IN))) {
                        printk("ip_local_deliver: bad non-lo skb: ");
                        debug_print_hooks_ip(skb->nf_debug);
                        nf_dump_skb(PF_INET, skb);
                }
        }
}

void nf_debug_ip_loopback_xmit(struct sk_buff *newskb)
{
        if (newskb->nf_debug != ((1 << NF_IP_LOCAL_OUT)
                                 | (1 << NF_IP_POST_ROUTING))) {
                printk("ip_dev_loopback_xmit: bad owned skb = %p: ", 
                       newskb);
                debug_print_hooks_ip(newskb->nf_debug);
                nf_dump_skb(PF_INET, newskb);
        }
        /* Clear to avoid confusing input check */
        newskb->nf_debug = 0;
}

void nf_debug_ip_finish_output2(struct sk_buff *skb)
{
        /* If it's owned, it must have gone through the
         * NF_IP_LOCAL_OUT and NF_IP_POST_ROUTING.
         * Otherwise, must have gone through
         * NF_IP_PRE_ROUTING, NF_IP_FORWARD and NF_IP_POST_ROUTING.
         */
        if (skb->sk) {
                if (skb->nf_debug != ((1 << NF_IP_LOCAL_OUT)
                                      | (1 << NF_IP_POST_ROUTING))) {
                        printk("ip_finish_output: bad owned skb = %p: ", skb);
                        debug_print_hooks_ip(skb->nf_debug);
                        nf_dump_skb(PF_INET, skb);
                }
        } else {
                if (skb->nf_debug != ((1 << NF_IP_PRE_ROUTING)
                                      | (1 << NF_IP_FORWARD)
                                      | (1 << NF_IP_POST_ROUTING))) {
                        /* Fragments, entunnelled packets, TCP RSTs
                           generated by ipt_REJECT will have no
                           owners, but still may be local */
                        if (skb->nf_debug != ((1 << NF_IP_LOCAL_OUT)
                                              | (1 << NF_IP_POST_ROUTING))){
                                printk("ip_finish_output:"
                                       " bad unowned skb = %p: ",skb);
                                debug_print_hooks_ip(skb->nf_debug);
                                nf_dump_skb(PF_INET, skb);
                        }
                }
        }
}
#endif /*CONFIG_NETFILTER_DEBUG*/

/* Call get/setsockopt() */
static int nf_sockopt(struct sock *sk, int pf, int val, 
                      char *opt, int *len, int get)
{
        struct list_head *i;
        struct nf_sockopt_ops *ops;
        int ret;

        if (down_interruptible(&nf_sockopt_mutex) != 0)
                return -EINTR;

        for (i = nf_sockopts.next; i != &nf_sockopts; i = i->next) {
                ops = (struct nf_sockopt_ops *)i;
                if (ops->pf == pf) {
                        if (get) {
                                if (val >= ops->get_optmin
                                    && val < ops->get_optmax) {
                                        ops->use++;
                                        up(&nf_sockopt_mutex);
                                        ret = ops->get(sk, val, opt, len);
                                        goto out;
                                }
                        } else {
                                if (val >= ops->set_optmin
                                    && val < ops->set_optmax) {
                                        ops->use++;
                                        up(&nf_sockopt_mutex);
                                        ret = ops->set(sk, val, opt, *len);
                                        goto out;
                                }
                        }
                }
        }
        up(&nf_sockopt_mutex);
        return -ENOPROTOOPT;
        
 out:
        down(&nf_sockopt_mutex);
        ops->use--;
        if (ops->cleanup_task)
                wake_up_process(ops->cleanup_task);
        up(&nf_sockopt_mutex);
        return ret;
}

int nf_setsockopt(struct sock *sk, int pf, int val, char *opt,
                  int len)
{
        return nf_sockopt(sk, pf, val, opt, &len, 0);
}

int nf_getsockopt(struct sock *sk, int pf, int val, char *opt, int *len)
{
        return nf_sockopt(sk, pf, val, opt, len, 1);
}

static unsigned int nf_iterate(struct list_head *head,
                               struct sk_buff **skb,
                               int hook,
                               const struct net_device *indev,
                               const struct net_device *outdev,
                               struct list_head **i,
                               int (*okfn)(struct sk_buff *))
{
        for (*i = (*i)->next; *i != head; *i = (*i)->next) {
                struct nf_hook_ops *elem = (struct nf_hook_ops *)*i;
                switch (elem->hook(hook, skb, indev, outdev, okfn)) {
                case NF_QUEUE:
                        return NF_QUEUE;

                case NF_STOLEN:
                        return NF_STOLEN;

                case NF_DROP:
                        return NF_DROP;

                case NF_REPEAT:
                        *i = (*i)->prev;
                        break;

#ifdef CONFIG_NETFILTER_DEBUG
                case NF_ACCEPT:
                        break;

                default:
                        NFDEBUG("Evil return from %p(%u).\n", 
                                elem->hook, hook);
#endif
                }
        }
        return NF_ACCEPT;
}

int nf_register_queue_handler(int pf, nf_queue_outfn_t outfn, void *data)
{      
        int ret;

        br_write_lock_bh(BR_NETPROTO_LOCK);
        if (queue_handler[pf].outfn)
                ret = -EBUSY;
        else {
                queue_handler[pf].outfn = outfn;
                queue_handler[pf].data = data;
                ret = 0;
        }
        br_write_unlock_bh(BR_NETPROTO_LOCK);

        return ret;
}

/* The caller must flush their queue before this */
int nf_unregister_queue_handler(int pf)
{
        br_write_lock_bh(BR_NETPROTO_LOCK);
        queue_handler[pf].outfn = NULL;
        queue_handler[pf].data = NULL;
        br_write_unlock_bh(BR_NETPROTO_LOCK);
        return 0;
}

/* 
 * Any packet that leaves via this function must come back 
 * through nf_reinject().
 */
static void nf_queue(struct sk_buff *skb, 
                     struct list_head *elem, 
                     int pf, unsigned int hook,
                     struct net_device *indev,
                     struct net_device *outdev,
                     int (*okfn)(struct sk_buff *))
{
        int status;
        struct nf_info *info;

        if (!queue_handler[pf].outfn) {
                kfree_skb(skb);
                return;
        }

        info = kmalloc(sizeof(*info), GFP_ATOMIC);
        if (!info) {
                if (net_ratelimit())
                        printk(KERN_ERR "OOM queueing packet %p\n",
                               skb);
                kfree_skb(skb);
                return;
        }

        *info = (struct nf_info) { 
                (struct nf_hook_ops *)elem, pf, hook, indev, outdev, okfn };

        /* Bump dev refs so they don't vanish while packet is out */
        if (indev) dev_hold(indev);
        if (outdev) dev_hold(outdev);

        status = queue_handler[pf].outfn(skb, info, queue_handler[pf].data);
        if (status < 0) {
                /* James M doesn't say fuck enough. */
                if (indev) dev_put(indev);
                if (outdev) dev_put(outdev);
                kfree(info);
                kfree_skb(skb);
                return;
        }
}

int nf_hook_slow(int pf, unsigned int hook, struct sk_buff *skb,
                 struct net_device *indev,
                 struct net_device *outdev,
                 int (*okfn)(struct sk_buff *))
{
        struct list_head *elem;
        unsigned int verdict;
        int ret = 0;

        /* This stopgap cannot be removed until all the hooks are audited. */
        if (skb_is_nonlinear(skb) && skb_linearize(skb, GFP_ATOMIC) != 0) {
                kfree_skb(skb);
                return -ENOMEM;
        }
        if (skb->ip_summed == CHECKSUM_HW) {
                if (outdev == NULL) {
                        skb->ip_summed = CHECKSUM_NONE;
                } else {
                        skb_checksum_help(skb);
                }
        }

        /* We may already have this, but read-locks nest anyway */
        br_read_lock_bh(BR_NETPROTO_LOCK);

#ifdef CONFIG_NETFILTER_DEBUG
        if (skb->nf_debug & (1 << hook)) {
                printk("nf_hook: hook %i already set.\n", hook);
                nf_dump_skb(pf, skb);
        }
        skb->nf_debug |= (1 << hook);
#endif

        elem = &nf_hooks[pf][hook];
        verdict = nf_iterate(&nf_hooks[pf][hook], &skb, hook, indev,
                             outdev, &elem, okfn);
        if (verdict == NF_QUEUE) {
                NFDEBUG("nf_hook: Verdict = QUEUE.\n");
                nf_queue(skb, elem, pf, hook, indev, outdev, okfn);
        }

        switch (verdict) {
        case NF_ACCEPT:
                ret = okfn(skb);
                break;

        case NF_DROP:
                kfree_skb(skb);
                ret = -EPERM;
                break;
        }

        br_read_unlock_bh(BR_NETPROTO_LOCK);
        return ret;
}

void nf_reinject(struct sk_buff *skb, struct nf_info *info,
                 unsigned int verdict)
{
        struct list_head *elem = &info->elem->list;
        struct list_head *i;

        /* We don't have BR_NETPROTO_LOCK here */
        br_read_lock_bh(BR_NETPROTO_LOCK);
        for (i = nf_hooks[info->pf][info->hook].next; i != elem; i = i->next) {
                if (i == &nf_hooks[info->pf][info->hook]) {
                        /* The module which sent it to userspace is gone. */
                        NFDEBUG("%s: module disappeared, dropping packet.\n",
                                 __FUNCTION__);
                        verdict = NF_DROP;
                        break;
                }
        }

        /* Continue traversal iff userspace said ok... */
        if (verdict == NF_REPEAT) {
                elem = elem->prev;
                verdict = NF_ACCEPT;
        }

        if (verdict == NF_ACCEPT) {
                verdict = nf_iterate(&nf_hooks[info->pf][info->hook],
                                     &skb, info->hook, 
                                     info->indev, info->outdev, &elem,
                                     info->okfn);
        }

        switch (verdict) {
        case NF_ACCEPT:
                info->okfn(skb);
                break;

        case NF_QUEUE:
                nf_queue(skb, elem, info->pf, info->hook, 
                         info->indev, info->outdev, info->okfn);
                break;

        case NF_DROP:
                kfree_skb(skb);
                break;
        }
        br_read_unlock_bh(BR_NETPROTO_LOCK);

        /* Release those devices we held, or Alexey will kill me. */
        if (info->indev) dev_put(info->indev);
        if (info->outdev) dev_put(info->outdev);
        
        kfree(info);
        return;
}

#ifdef CONFIG_INET
/* route_me_harder function, used by iptable_nat, iptable_mangle + ip_queue */
int ip_route_me_harder(struct sk_buff **pskb)
{
        struct iphdr *iph = (*pskb)->nh.iph;
        struct rtable *rt;
        struct rt_key key = {};
        struct dst_entry *odst;
        unsigned int hh_len;

        /* some non-standard hacks like ipt_REJECT.c:send_reset() can cause
         * packets with foreign saddr to be appear on the NF_IP_LOCAL_OUT hook.
         */
        if (inet_addr_type(iph->saddr) == RTN_LOCAL) {
                key.dst = iph->daddr;
                key.src = iph->saddr;
                key.oif = (*pskb)->sk ? (*pskb)->sk->bound_dev_if : 0;
                key.tos = RT_TOS(iph->tos);
#ifdef CONFIG_IP_ROUTE_FWMARK
                key.fwmark = (*pskb)->nfmark;
#endif
                if (ip_route_output_key(&rt, &key) != 0)
                        return -1;

                /* Drop old route. */
                dst_release((*pskb)->dst);
                (*pskb)->dst = &rt->u.dst;
        } else {
                /* non-local src, find valid iif to satisfy
                 * rp-filter when calling ip_route_input. */
                key.dst = iph->saddr;
                if (ip_route_output_key(&rt, &key) != 0)
                        return -1;

                odst = (*pskb)->dst;
                if (ip_route_input(*pskb, iph->daddr, iph->saddr,
                                   RT_TOS(iph->tos), rt->u.dst.dev) != 0) {
                        dst_release(&rt->u.dst);
                        return -1;
                }
                dst_release(&rt->u.dst);
                dst_release(odst);
        }
        
        if ((*pskb)->dst->error)
                return -1;

        /* Change in oif may mean change in hh_len. */
        hh_len = (*pskb)->dst->dev->hard_header_len;
        if (skb_headroom(*pskb) < hh_len) {
                struct sk_buff *nskb;

                nskb = skb_realloc_headroom(*pskb, hh_len);
                if (!nskb)
                        return -1;
                if ((*pskb)->sk)
                        skb_set_owner_w(nskb, (*pskb)->sk);
                kfree_skb(*pskb);
                *pskb = nskb;
        }

        return 0;
}
#endif /*CONFIG_INET*/

/* This does not belong here, but ipt_REJECT needs it if connection
   tracking in use: without this, connection may not be in hash table,
   and hence manufactured ICMP or RST packets will not be associated
   with it. */
void (*ip_ct_attach)(struct sk_buff *, struct nf_ct_info *);

void __init netfilter_init(void)
{
        int i, h;

        for (i = 0; i < NPROTO; i++) {
                for (h = 0; h < NF_MAX_HOOKS; h++)
                        INIT_LIST_HEAD(&nf_hooks[i][h]);
        }
}

---