Linux-2.6.12-rc2

[mirror_ubuntu-bionic-kernel.git] / net / ipv4 / netfilter / ip_tables.c

/*
 * Packet matching code.
 *
 * Copyright (C) 1999 Paul `Rusty' Russell & Michael J. Neuling
 * Copyright (C) 2000-2004 Netfilter Core Team <coreteam@netfilter.org>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 * 19 Jan 2002 Harald Welte <laforge@gnumonks.org>
 *      - increase module usage count as soon as we have rules inside
 *        a table
 */
#include <linux/config.h>
#include <linux/cache.h>
#include <linux/skbuff.h>
#include <linux/kmod.h>
#include <linux/vmalloc.h>
#include <linux/netdevice.h>
#include <linux/module.h>
#include <linux/tcp.h>
#include <linux/udp.h>
#include <linux/icmp.h>
#include <net/ip.h>
#include <asm/uaccess.h>
#include <asm/semaphore.h>
#include <linux/proc_fs.h>
#include <linux/err.h>

#include <linux/netfilter_ipv4/ip_tables.h>

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Netfilter Core Team <coreteam@netfilter.org>");
MODULE_DESCRIPTION("IPv4 packet filter");

/*#define DEBUG_IP_FIREWALL*/
/*#define DEBUG_ALLOW_ALL*/ /* Useful for remote debugging */
/*#define DEBUG_IP_FIREWALL_USER*/

#ifdef DEBUG_IP_FIREWALL
#define dprintf(format, args...)  printk(format , ## args)
#else
#define dprintf(format, args...)
#endif

#ifdef DEBUG_IP_FIREWALL_USER
#define duprintf(format, args...) printk(format , ## args)
#else
#define duprintf(format, args...)
#endif

#ifdef CONFIG_NETFILTER_DEBUG
#define IP_NF_ASSERT(x)                                         \
do {                                                            \
        if (!(x))                                               \
                printk("IP_NF_ASSERT: %s:%s:%u\n",              \
                       __FUNCTION__, __FILE__, __LINE__);       \
} while(0)
#else
#define IP_NF_ASSERT(x)
#endif
#define SMP_ALIGN(x) (((x) + SMP_CACHE_BYTES-1) & ~(SMP_CACHE_BYTES-1))

static DECLARE_MUTEX(ipt_mutex);

/* Must have mutex */
#define ASSERT_READ_LOCK(x) IP_NF_ASSERT(down_trylock(&ipt_mutex) != 0)
#define ASSERT_WRITE_LOCK(x) IP_NF_ASSERT(down_trylock(&ipt_mutex) != 0)
#include <linux/netfilter_ipv4/lockhelp.h>
#include <linux/netfilter_ipv4/listhelp.h>

#if 0
/* All the better to debug you with... */
#define static
#define inline
#endif

/*
   We keep a set of rules for each CPU, so we can avoid write-locking
   them in the softirq when updating the counters and therefore
   only need to read-lock in the softirq; doing a write_lock_bh() in user
   context stops packets coming through and allows user context to read
   the counters or update the rules.

   To be cache friendly on SMP, we arrange them like so:
   [ n-entries ]
   ... cache-align padding ...
   [ n-entries ]

   Hence the start of any table is given by get_table() below.  */

/* The table itself */
struct ipt_table_info
{
        /* Size per table */
        unsigned int size;
        /* Number of entries: FIXME. --RR */
        unsigned int number;
        /* Initial number of entries. Needed for module usage count */
        unsigned int initial_entries;

        /* Entry points and underflows */
        unsigned int hook_entry[NF_IP_NUMHOOKS];
        unsigned int underflow[NF_IP_NUMHOOKS];

        /* ipt_entry tables: one per CPU */
        char entries[0] ____cacheline_aligned;
};

static LIST_HEAD(ipt_target);
static LIST_HEAD(ipt_match);
static LIST_HEAD(ipt_tables);
#define ADD_COUNTER(c,b,p) do { (c).bcnt += (b); (c).pcnt += (p); } while(0)

#ifdef CONFIG_SMP
#define TABLE_OFFSET(t,p) (SMP_ALIGN((t)->size)*(p))
#else
#define TABLE_OFFSET(t,p) 0
#endif

#if 0
#define down(x) do { printk("DOWN:%u:" #x "\n", __LINE__); down(x); } while(0)
#define down_interruptible(x) ({ int __r; printk("DOWNi:%u:" #x "\n", __LINE__); __r = down_interruptible(x); if (__r != 0) printk("ABORT-DOWNi:%u\n", __LINE__); __r; })
#define up(x) do { printk("UP:%u:" #x "\n", __LINE__); up(x); } while(0)
#endif

/* Returns whether matches rule or not. */
static inline int
ip_packet_match(const struct iphdr *ip,
                const char *indev,
                const char *outdev,
                const struct ipt_ip *ipinfo,
                int isfrag)
{
        size_t i;
        unsigned long ret;

#define FWINV(bool,invflg) ((bool) ^ !!(ipinfo->invflags & invflg))

        if (FWINV((ip->saddr&ipinfo->smsk.s_addr) != ipinfo->src.s_addr,
                  IPT_INV_SRCIP)
            || FWINV((ip->daddr&ipinfo->dmsk.s_addr) != ipinfo->dst.s_addr,
                     IPT_INV_DSTIP)) {
                dprintf("Source or dest mismatch.\n");

                dprintf("SRC: %u.%u.%u.%u. Mask: %u.%u.%u.%u. Target: %u.%u.%u.%u.%s\n",
                        NIPQUAD(ip->saddr),
                        NIPQUAD(ipinfo->smsk.s_addr),
                        NIPQUAD(ipinfo->src.s_addr),
                        ipinfo->invflags & IPT_INV_SRCIP ? " (INV)" : "");
                dprintf("DST: %u.%u.%u.%u Mask: %u.%u.%u.%u Target: %u.%u.%u.%u.%s\n",
                        NIPQUAD(ip->daddr),
                        NIPQUAD(ipinfo->dmsk.s_addr),
                        NIPQUAD(ipinfo->dst.s_addr),
                        ipinfo->invflags & IPT_INV_DSTIP ? " (INV)" : "");
                return 0;
        }

        /* Look for ifname matches; this should unroll nicely. */
        for (i = 0, ret = 0; i < IFNAMSIZ/sizeof(unsigned long); i++) {
                ret |= (((const unsigned long *)indev)[i]
                        ^ ((const unsigned long *)ipinfo->iniface)[i])
                        & ((const unsigned long *)ipinfo->iniface_mask)[i];
        }

        if (FWINV(ret != 0, IPT_INV_VIA_IN)) {
                dprintf("VIA in mismatch (%s vs %s).%s\n",
                        indev, ipinfo->iniface,
                        ipinfo->invflags&IPT_INV_VIA_IN ?" (INV)":"");
                return 0;
        }

        for (i = 0, ret = 0; i < IFNAMSIZ/sizeof(unsigned long); i++) {
                ret |= (((const unsigned long *)outdev)[i]
                        ^ ((const unsigned long *)ipinfo->outiface)[i])
                        & ((const unsigned long *)ipinfo->outiface_mask)[i];
        }

        if (FWINV(ret != 0, IPT_INV_VIA_OUT)) {
                dprintf("VIA out mismatch (%s vs %s).%s\n",
                        outdev, ipinfo->outiface,
                        ipinfo->invflags&IPT_INV_VIA_OUT ?" (INV)":"");
                return 0;
        }

        /* Check specific protocol */
        if (ipinfo->proto
            && FWINV(ip->protocol != ipinfo->proto, IPT_INV_PROTO)) {
                dprintf("Packet protocol %hi does not match %hi.%s\n",
                        ip->protocol, ipinfo->proto,
                        ipinfo->invflags&IPT_INV_PROTO ? " (INV)":"");
                return 0;
        }

        /* If we have a fragment rule but the packet is not a fragment
         * then we return zero */
        if (FWINV((ipinfo->flags&IPT_F_FRAG) && !isfrag, IPT_INV_FRAG)) {
                dprintf("Fragment rule but not fragment.%s\n",
                        ipinfo->invflags & IPT_INV_FRAG ? " (INV)" : "");
                return 0;
        }

        return 1;
}

static inline int
ip_checkentry(const struct ipt_ip *ip)
{
        if (ip->flags & ~IPT_F_MASK) {
                duprintf("Unknown flag bits set: %08X\n",
                         ip->flags & ~IPT_F_MASK);
                return 0;
        }
        if (ip->invflags & ~IPT_INV_MASK) {
                duprintf("Unknown invflag bits set: %08X\n",
                         ip->invflags & ~IPT_INV_MASK);
                return 0;
        }
        return 1;
}

static unsigned int
ipt_error(struct sk_buff **pskb,
          const struct net_device *in,
          const struct net_device *out,
          unsigned int hooknum,
          const void *targinfo,
          void *userinfo)
{
        if (net_ratelimit())
                printk("ip_tables: error: `%s'\n", (char *)targinfo);

        return NF_DROP;
}

static inline
int do_match(struct ipt_entry_match *m,
             const struct sk_buff *skb,
             const struct net_device *in,
             const struct net_device *out,
             int offset,
             int *hotdrop)
{
        /* Stop iteration if it doesn't match */
        if (!m->u.kernel.match->match(skb, in, out, m->data, offset, hotdrop))
                return 1;
        else
                return 0;
}

static inline struct ipt_entry *
get_entry(void *base, unsigned int offset)
{
        return (struct ipt_entry *)(base + offset);
}

/* Returns one of the generic firewall policies, like NF_ACCEPT. */
unsigned int
ipt_do_table(struct sk_buff **pskb,
             unsigned int hook,
             const struct net_device *in,
             const struct net_device *out,
             struct ipt_table *table,
             void *userdata)
{
        static const char nulldevname[IFNAMSIZ] __attribute__((aligned(sizeof(long))));
        u_int16_t offset;
        struct iphdr *ip;
        u_int16_t datalen;
        int hotdrop = 0;
        /* Initializing verdict to NF_DROP keeps gcc happy. */
        unsigned int verdict = NF_DROP;
        const char *indev, *outdev;
        void *table_base;
        struct ipt_entry *e, *back;

        /* Initialization */
        ip = (*pskb)->nh.iph;
        datalen = (*pskb)->len - ip->ihl * 4;
        indev = in ? in->name : nulldevname;
        outdev = out ? out->name : nulldevname;
        /* We handle fragments by dealing with the first fragment as
         * if it was a normal packet.  All other fragments are treated
         * normally, except that they will NEVER match rules that ask
         * things we don't know, ie. tcp syn flag or ports).  If the
         * rule is also a fragment-specific rule, non-fragments won't
         * match it. */
        offset = ntohs(ip->frag_off) & IP_OFFSET;

        read_lock_bh(&table->lock);
        IP_NF_ASSERT(table->valid_hooks & (1 << hook));
        table_base = (void *)table->private->entries
                + TABLE_OFFSET(table->private, smp_processor_id());
        e = get_entry(table_base, table->private->hook_entry[hook]);

#ifdef CONFIG_NETFILTER_DEBUG
        /* Check noone else using our table */
        if (((struct ipt_entry *)table_base)->comefrom != 0xdead57ac
            && ((struct ipt_entry *)table_base)->comefrom != 0xeeeeeeec) {
                printk("ASSERT: CPU #%u, %s comefrom(%p) = %X\n",
                       smp_processor_id(),
                       table->name,
                       &((struct ipt_entry *)table_base)->comefrom,
                       ((struct ipt_entry *)table_base)->comefrom);
        }
        ((struct ipt_entry *)table_base)->comefrom = 0x57acc001;
#endif

        /* For return from builtin chain */
        back = get_entry(table_base, table->private->underflow[hook]);

        do {
                IP_NF_ASSERT(e);
                IP_NF_ASSERT(back);
                (*pskb)->nfcache |= e->nfcache;
                if (ip_packet_match(ip, indev, outdev, &e->ip, offset)) {
                        struct ipt_entry_target *t;

                        if (IPT_MATCH_ITERATE(e, do_match,
                                              *pskb, in, out,
                                              offset, &hotdrop) != 0)
                                goto no_match;

                        ADD_COUNTER(e->counters, ntohs(ip->tot_len), 1);

                        t = ipt_get_target(e);
                        IP_NF_ASSERT(t->u.kernel.target);
                        /* Standard target? */
                        if (!t->u.kernel.target->target) {
                                int v;

                                v = ((struct ipt_standard_target *)t)->verdict;
                                if (v < 0) {
                                        /* Pop from stack? */
                                        if (v != IPT_RETURN) {
                                                verdict = (unsigned)(-v) - 1;
                                                break;
                                        }
                                        e = back;
                                        back = get_entry(table_base,
                                                         back->comefrom);
                                        continue;
                                }
                                if (table_base + v
                                    != (void *)e + e->next_offset) {
                                        /* Save old back ptr in next entry */
                                        struct ipt_entry *next
                                                = (void *)e + e->next_offset;
                                        next->comefrom
                                                = (void *)back - table_base;
                                        /* set back pointer to next entry */
                                        back = next;
                                }

                                e = get_entry(table_base, v);
                        } else {
                                /* Targets which reenter must return
                                   abs. verdicts */
#ifdef CONFIG_NETFILTER_DEBUG
                                ((struct ipt_entry *)table_base)->comefrom
                                        = 0xeeeeeeec;
#endif
                                verdict = t->u.kernel.target->target(pskb,
                                                                     in, out,
                                                                     hook,
                                                                     t->data,
                                                                     userdata);

#ifdef CONFIG_NETFILTER_DEBUG
                                if (((struct ipt_entry *)table_base)->comefrom
                                    != 0xeeeeeeec
                                    && verdict == IPT_CONTINUE) {
                                        printk("Target %s reentered!\n",
                                               t->u.kernel.target->name);
                                        verdict = NF_DROP;
                                }
                                ((struct ipt_entry *)table_base)->comefrom
                                        = 0x57acc001;
#endif
                                /* Target might have changed stuff. */
                                ip = (*pskb)->nh.iph;
                                datalen = (*pskb)->len - ip->ihl * 4;

                                if (verdict == IPT_CONTINUE)
                                        e = (void *)e + e->next_offset;
                                else
                                        /* Verdict */
                                        break;
                        }
                } else {

                no_match:
                        e = (void *)e + e->next_offset;
                }
        } while (!hotdrop);

#ifdef CONFIG_NETFILTER_DEBUG
        ((struct ipt_entry *)table_base)->comefrom = 0xdead57ac;
#endif
        read_unlock_bh(&table->lock);

#ifdef DEBUG_ALLOW_ALL
        return NF_ACCEPT;
#else
        if (hotdrop)
                return NF_DROP;
        else return verdict;
#endif
}

/*
 * These are weird, but module loading must not be done with mutex
 * held (since they will register), and we have to have a single
 * function to use try_then_request_module().
 */

/* Find table by name, grabs mutex & ref.  Returns ERR_PTR() on error. */
static inline struct ipt_table *find_table_lock(const char *name)
{
        struct ipt_table *t;

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

        list_for_each_entry(t, &ipt_tables, list)
                if (strcmp(t->name, name) == 0 && try_module_get(t->me))
                        return t;
        up(&ipt_mutex);
        return NULL;
}

/* Find match, grabs ref.  Returns ERR_PTR() on error. */
static inline struct ipt_match *find_match(const char *name, u8 revision)
{
        struct ipt_match *m;
        int err = 0;

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

        list_for_each_entry(m, &ipt_match, list) {
                if (strcmp(m->name, name) == 0) {
                        if (m->revision == revision) {
                                if (try_module_get(m->me)) {
                                        up(&ipt_mutex);
                                        return m;
                                }
                        } else
                                err = -EPROTOTYPE; /* Found something. */
                }
        }
        up(&ipt_mutex);
        return ERR_PTR(err);
}

/* Find target, grabs ref.  Returns ERR_PTR() on error. */
static inline struct ipt_target *find_target(const char *name, u8 revision)
{
        struct ipt_target *t;
        int err = 0;

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

        list_for_each_entry(t, &ipt_target, list) {
                if (strcmp(t->name, name) == 0) {
                        if (t->revision == revision) {
                                if (try_module_get(t->me)) {
                                        up(&ipt_mutex);
                                        return t;
                                }
                        } else
                                err = -EPROTOTYPE; /* Found something. */
                }
        }
        up(&ipt_mutex);
        return ERR_PTR(err);
}

struct ipt_target *ipt_find_target(const char *name, u8 revision)
{
        struct ipt_target *target;

        target = try_then_request_module(find_target(name, revision),
                                         "ipt_%s", name);
        if (IS_ERR(target) || !target)
                return NULL;
        return target;
}

static int match_revfn(const char *name, u8 revision, int *bestp)
{
        struct ipt_match *m;
        int have_rev = 0;

        list_for_each_entry(m, &ipt_match, list) {
                if (strcmp(m->name, name) == 0) {
                        if (m->revision > *bestp)
                                *bestp = m->revision;
                        if (m->revision == revision)
                                have_rev = 1;
                }
        }
        return have_rev;
}

static int target_revfn(const char *name, u8 revision, int *bestp)
{
        struct ipt_target *t;
        int have_rev = 0;

        list_for_each_entry(t, &ipt_target, list) {
                if (strcmp(t->name, name) == 0) {
                        if (t->revision > *bestp)
                                *bestp = t->revision;
                        if (t->revision == revision)
                                have_rev = 1;
                }
        }
        return have_rev;
}

/* Returns true or false (if no such extension at all) */
static inline int find_revision(const char *name, u8 revision,
                                int (*revfn)(const char *, u8, int *),
                                int *err)
{
        int have_rev, best = -1;

        if (down_interruptible(&ipt_mutex) != 0) {
                *err = -EINTR;
                return 1;
        }
        have_rev = revfn(name, revision, &best);
        up(&ipt_mutex);

        /* Nothing at all?  Return 0 to try loading module. */
        if (best == -1) {
                *err = -ENOENT;
                return 0;
        }

        *err = best;
        if (!have_rev)
                *err = -EPROTONOSUPPORT;
        return 1;
}


/* All zeroes == unconditional rule. */
static inline int
unconditional(const struct ipt_ip *ip)
{
        unsigned int i;

        for (i = 0; i < sizeof(*ip)/sizeof(__u32); i++)
                if (((__u32 *)ip)[i])
                        return 0;

        return 1;
}

/* Figures out from what hook each rule can be called: returns 0 if
   there are loops.  Puts hook bitmask in comefrom. */
static int
mark_source_chains(struct ipt_table_info *newinfo, unsigned int valid_hooks)
{
        unsigned int hook;

        /* No recursion; use packet counter to save back ptrs (reset
           to 0 as we leave), and comefrom to save source hook bitmask */
        for (hook = 0; hook < NF_IP_NUMHOOKS; hook++) {
                unsigned int pos = newinfo->hook_entry[hook];
                struct ipt_entry *e
                        = (struct ipt_entry *)(newinfo->entries + pos);

                if (!(valid_hooks & (1 << hook)))
                        continue;

                /* Set initial back pointer. */
                e->counters.pcnt = pos;

                for (;;) {
                        struct ipt_standard_target *t
                                = (void *)ipt_get_target(e);

                        if (e->comefrom & (1 << NF_IP_NUMHOOKS)) {
                                printk("iptables: loop hook %u pos %u %08X.\n",
                                       hook, pos, e->comefrom);
                                return 0;
                        }
                        e->comefrom
                                |= ((1 << hook) | (1 << NF_IP_NUMHOOKS));

                        /* Unconditional return/END. */
                        if (e->target_offset == sizeof(struct ipt_entry)
                            && (strcmp(t->target.u.user.name,
                                       IPT_STANDARD_TARGET) == 0)
                            && t->verdict < 0
                            && unconditional(&e->ip)) {
                                unsigned int oldpos, size;

                                /* Return: backtrack through the last
                                   big jump. */
                                do {
                                        e->comefrom ^= (1<<NF_IP_NUMHOOKS);
#ifdef DEBUG_IP_FIREWALL_USER
                                        if (e->comefrom
                                            & (1 << NF_IP_NUMHOOKS)) {
                                                duprintf("Back unset "
                                                         "on hook %u "
                                                         "rule %u\n",
                                                         hook, pos);
                                        }
#endif
                                        oldpos = pos;
                                        pos = e->counters.pcnt;
                                        e->counters.pcnt = 0;

                                        /* We're at the start. */
                                        if (pos == oldpos)
                                                goto next;

                                        e = (struct ipt_entry *)
                                                (newinfo->entries + pos);
                                } while (oldpos == pos + e->next_offset);

                                /* Move along one */
                                size = e->next_offset;
                                e = (struct ipt_entry *)
                                        (newinfo->entries + pos + size);
                                e->counters.pcnt = pos;
                                pos += size;
                        } else {
                                int newpos = t->verdict;

                                if (strcmp(t->target.u.user.name,
                                           IPT_STANDARD_TARGET) == 0
                                    && newpos >= 0) {
                                        /* This a jump; chase it. */
                                        duprintf("Jump rule %u -> %u\n",
                                                 pos, newpos);
                                } else {
                                        /* ... this is a fallthru */
                                        newpos = pos + e->next_offset;
                                }
                                e = (struct ipt_entry *)
                                        (newinfo->entries + newpos);
                                e->counters.pcnt = pos;
                                pos = newpos;
                        }
                }
                next:
                duprintf("Finished chain %u\n", hook);
        }
        return 1;
}

static inline int
cleanup_match(struct ipt_entry_match *m, unsigned int *i)
{
        if (i && (*i)-- == 0)
                return 1;

        if (m->u.kernel.match->destroy)
                m->u.kernel.match->destroy(m->data,
                                           m->u.match_size - sizeof(*m));
        module_put(m->u.kernel.match->me);
        return 0;
}

static inline int
standard_check(const struct ipt_entry_target *t,
               unsigned int max_offset)
{
        struct ipt_standard_target *targ = (void *)t;

        /* Check standard info. */
        if (t->u.target_size
            != IPT_ALIGN(sizeof(struct ipt_standard_target))) {
                duprintf("standard_check: target size %u != %u\n",
                         t->u.target_size,
                         IPT_ALIGN(sizeof(struct ipt_standard_target)));
                return 0;
        }

        if (targ->verdict >= 0
            && targ->verdict > max_offset - sizeof(struct ipt_entry)) {
                duprintf("ipt_standard_check: bad verdict (%i)\n",
                         targ->verdict);
                return 0;
        }

        if (targ->verdict < -NF_MAX_VERDICT - 1) {
                duprintf("ipt_standard_check: bad negative verdict (%i)\n",
                         targ->verdict);
                return 0;
        }
        return 1;
}

static inline int
check_match(struct ipt_entry_match *m,
            const char *name,
            const struct ipt_ip *ip,
            unsigned int hookmask,
            unsigned int *i)
{
        struct ipt_match *match;

        match = try_then_request_module(find_match(m->u.user.name,
                                                   m->u.user.revision),
                                        "ipt_%s", m->u.user.name);
        if (IS_ERR(match) || !match) {
                duprintf("check_match: `%s' not found\n", m->u.user.name);
                return match ? PTR_ERR(match) : -ENOENT;
        }
        m->u.kernel.match = match;

        if (m->u.kernel.match->checkentry
            && !m->u.kernel.match->checkentry(name, ip, m->data,
                                              m->u.match_size - sizeof(*m),
                                              hookmask)) {
                module_put(m->u.kernel.match->me);
                duprintf("ip_tables: check failed for `%s'.\n",
                         m->u.kernel.match->name);
                return -EINVAL;
        }

        (*i)++;
        return 0;
}

static struct ipt_target ipt_standard_target;

static inline int
check_entry(struct ipt_entry *e, const char *name, unsigned int size,
            unsigned int *i)
{
        struct ipt_entry_target *t;
        struct ipt_target *target;
        int ret;
        unsigned int j;

        if (!ip_checkentry(&e->ip)) {
                duprintf("ip_tables: ip check failed %p %s.\n", e, name);
                return -EINVAL;
        }

        j = 0;
        ret = IPT_MATCH_ITERATE(e, check_match, name, &e->ip, e->comefrom, &j);
        if (ret != 0)
                goto cleanup_matches;

        t = ipt_get_target(e);
        target = try_then_request_module(find_target(t->u.user.name,
                                                     t->u.user.revision),
                                         "ipt_%s", t->u.user.name);
        if (IS_ERR(target) || !target) {
                duprintf("check_entry: `%s' not found\n", t->u.user.name);
                ret = target ? PTR_ERR(target) : -ENOENT;
                goto cleanup_matches;
        }
        t->u.kernel.target = target;

        if (t->u.kernel.target == &ipt_standard_target) {
                if (!standard_check(t, size)) {
                        ret = -EINVAL;
                        goto cleanup_matches;
                }
        } else if (t->u.kernel.target->checkentry
                   && !t->u.kernel.target->checkentry(name, e, t->data,
                                                      t->u.target_size
                                                      - sizeof(*t),
                                                      e->comefrom)) {
                module_put(t->u.kernel.target->me);
                duprintf("ip_tables: check failed for `%s'.\n",
                         t->u.kernel.target->name);
                ret = -EINVAL;
                goto cleanup_matches;
        }

        (*i)++;
        return 0;

 cleanup_matches:
        IPT_MATCH_ITERATE(e, cleanup_match, &j);
        return ret;
}

static inline int
check_entry_size_and_hooks(struct ipt_entry *e,
                           struct ipt_table_info *newinfo,
                           unsigned char *base,
                           unsigned char *limit,
                           const unsigned int *hook_entries,
                           const unsigned int *underflows,
                           unsigned int *i)
{
        unsigned int h;

        if ((unsigned long)e % __alignof__(struct ipt_entry) != 0
            || (unsigned char *)e + sizeof(struct ipt_entry) >= limit) {
                duprintf("Bad offset %p\n", e);
                return -EINVAL;
        }

        if (e->next_offset
            < sizeof(struct ipt_entry) + sizeof(struct ipt_entry_target)) {
                duprintf("checking: element %p size %u\n",
                         e, e->next_offset);
                return -EINVAL;
        }

        /* Check hooks & underflows */
        for (h = 0; h < NF_IP_NUMHOOKS; h++) {
                if ((unsigned char *)e - base == hook_entries[h])
                        newinfo->hook_entry[h] = hook_entries[h];
                if ((unsigned char *)e - base == underflows[h])
                        newinfo->underflow[h] = underflows[h];
        }

        /* FIXME: underflows must be unconditional, standard verdicts
           < 0 (not IPT_RETURN). --RR */

        /* Clear counters and comefrom */
        e->counters = ((struct ipt_counters) { 0, 0 });
        e->comefrom = 0;

        (*i)++;
        return 0;
}

static inline int
cleanup_entry(struct ipt_entry *e, unsigned int *i)
{
        struct ipt_entry_target *t;

        if (i && (*i)-- == 0)
                return 1;

        /* Cleanup all matches */
        IPT_MATCH_ITERATE(e, cleanup_match, NULL);
        t = ipt_get_target(e);
        if (t->u.kernel.target->destroy)
                t->u.kernel.target->destroy(t->data,
                                            t->u.target_size - sizeof(*t));
        module_put(t->u.kernel.target->me);
        return 0;
}

/* Checks and translates the user-supplied table segment (held in
   newinfo) */
static int
translate_table(const char *name,
                unsigned int valid_hooks,
                struct ipt_table_info *newinfo,
                unsigned int size,
                unsigned int number,
                const unsigned int *hook_entries,
                const unsigned int *underflows)
{
        unsigned int i;
        int ret;

        newinfo->size = size;
        newinfo->number = number;

        /* Init all hooks to impossible value. */
        for (i = 0; i < NF_IP_NUMHOOKS; i++) {
                newinfo->hook_entry[i] = 0xFFFFFFFF;
                newinfo->underflow[i] = 0xFFFFFFFF;
        }

        duprintf("translate_table: size %u\n", newinfo->size);
        i = 0;
        /* Walk through entries, checking offsets. */
        ret = IPT_ENTRY_ITERATE(newinfo->entries, newinfo->size,
                                check_entry_size_and_hooks,
                                newinfo,
                                newinfo->entries,
                                newinfo->entries + size,
                                hook_entries, underflows, &i);
        if (ret != 0)
                return ret;

        if (i != number) {
                duprintf("translate_table: %u not %u entries\n",
                         i, number);
                return -EINVAL;
        }

        /* Check hooks all assigned */
        for (i = 0; i < NF_IP_NUMHOOKS; i++) {
                /* Only hooks which are valid */
                if (!(valid_hooks & (1 << i)))
                        continue;
                if (newinfo->hook_entry[i] == 0xFFFFFFFF) {
                        duprintf("Invalid hook entry %u %u\n",
                                 i, hook_entries[i]);
                        return -EINVAL;
                }
                if (newinfo->underflow[i] == 0xFFFFFFFF) {
                        duprintf("Invalid underflow %u %u\n",
                                 i, underflows[i]);
                        return -EINVAL;
                }
        }

        if (!mark_source_chains(newinfo, valid_hooks))
                return -ELOOP;

        /* Finally, each sanity check must pass */
        i = 0;
        ret = IPT_ENTRY_ITERATE(newinfo->entries, newinfo->size,
                                check_entry, name, size, &i);

        if (ret != 0) {
                IPT_ENTRY_ITERATE(newinfo->entries, newinfo->size,
                                  cleanup_entry, &i);
                return ret;
        }

        /* And one copy for every other CPU */
        for (i = 1; i < num_possible_cpus(); i++) {
                memcpy(newinfo->entries + SMP_ALIGN(newinfo->size)*i,
                       newinfo->entries,
                       SMP_ALIGN(newinfo->size));
        }

        return ret;
}

static struct ipt_table_info *
replace_table(struct ipt_table *table,
              unsigned int num_counters,
              struct ipt_table_info *newinfo,
              int *error)
{
        struct ipt_table_info *oldinfo;

#ifdef CONFIG_NETFILTER_DEBUG
        {
                struct ipt_entry *table_base;
                unsigned int i;

                for (i = 0; i < num_possible_cpus(); i++) {
                        table_base =
                                (void *)newinfo->entries
                                + TABLE_OFFSET(newinfo, i);

                        table_base->comefrom = 0xdead57ac;
                }
        }
#endif

        /* Do the substitution. */
        write_lock_bh(&table->lock);
        /* Check inside lock: is the old number correct? */
        if (num_counters != table->private->number) {
                duprintf("num_counters != table->private->number (%u/%u)\n",
                         num_counters, table->private->number);
                write_unlock_bh(&table->lock);
                *error = -EAGAIN;
                return NULL;
        }
        oldinfo = table->private;
        table->private = newinfo;
        newinfo->initial_entries = oldinfo->initial_entries;
        write_unlock_bh(&table->lock);

        return oldinfo;
}

/* Gets counters. */
static inline int
add_entry_to_counter(const struct ipt_entry *e,
                     struct ipt_counters total[],
                     unsigned int *i)
{
        ADD_COUNTER(total[*i], e->counters.bcnt, e->counters.pcnt);

        (*i)++;
        return 0;
}

static void
get_counters(const struct ipt_table_info *t,
             struct ipt_counters counters[])
{
        unsigned int cpu;
        unsigned int i;

        for (cpu = 0; cpu < num_possible_cpus(); cpu++) {
                i = 0;
                IPT_ENTRY_ITERATE(t->entries + TABLE_OFFSET(t, cpu),
                                  t->size,
                                  add_entry_to_counter,
                                  counters,
                                  &i);
        }
}

static int
copy_entries_to_user(unsigned int total_size,
                     struct ipt_table *table,
                     void __user *userptr)
{
        unsigned int off, num, countersize;
        struct ipt_entry *e;
        struct ipt_counters *counters;
        int ret = 0;

        /* We need atomic snapshot of counters: rest doesn't change
           (other than comefrom, which userspace doesn't care
           about). */
        countersize = sizeof(struct ipt_counters) * table->private->number;
        counters = vmalloc(countersize);

        if (counters == NULL)
                return -ENOMEM;

        /* First, sum counters... */
        memset(counters, 0, countersize);
        write_lock_bh(&table->lock);
        get_counters(table->private, counters);
        write_unlock_bh(&table->lock);

        /* ... then copy entire thing from CPU 0... */
        if (copy_to_user(userptr, table->private->entries, total_size) != 0) {
                ret = -EFAULT;
                goto free_counters;
        }

        /* FIXME: use iterator macros --RR */
        /* ... then go back and fix counters and names */
        for (off = 0, num = 0; off < total_size; off += e->next_offset, num++){
                unsigned int i;
                struct ipt_entry_match *m;
                struct ipt_entry_target *t;

                e = (struct ipt_entry *)(table->private->entries + off);
                if (copy_to_user(userptr + off
                                 + offsetof(struct ipt_entry, counters),
                                 &counters[num],
                                 sizeof(counters[num])) != 0) {
                        ret = -EFAULT;
                        goto free_counters;
                }

                for (i = sizeof(struct ipt_entry);
                     i < e->target_offset;
                     i += m->u.match_size) {
                        m = (void *)e + i;

                        if (copy_to_user(userptr + off + i
                                         + offsetof(struct ipt_entry_match,
                                                    u.user.name),
                                         m->u.kernel.match->name,
                                         strlen(m->u.kernel.match->name)+1)
                            != 0) {
                                ret = -EFAULT;
                                goto free_counters;
                        }
                }

                t = ipt_get_target(e);
                if (copy_to_user(userptr + off + e->target_offset
                                 + offsetof(struct ipt_entry_target,
                                            u.user.name),
                                 t->u.kernel.target->name,
                                 strlen(t->u.kernel.target->name)+1) != 0) {
                        ret = -EFAULT;
                        goto free_counters;
                }
        }

 free_counters:
        vfree(counters);
        return ret;
}

static int
get_entries(const struct ipt_get_entries *entries,
            struct ipt_get_entries __user *uptr)
{
        int ret;
        struct ipt_table *t;

        t = find_table_lock(entries->name);
        if (t && !IS_ERR(t)) {
                duprintf("t->private->number = %u\n",
                         t->private->number);
                if (entries->size == t->private->size)
                        ret = copy_entries_to_user(t->private->size,
                                                   t, uptr->entrytable);
                else {
                        duprintf("get_entries: I've got %u not %u!\n",
                                 t->private->size,
                                 entries->size);
                        ret = -EINVAL;
                }
                module_put(t->me);
                up(&ipt_mutex);
        } else
                ret = t ? PTR_ERR(t) : -ENOENT;

        return ret;
}

static int
do_replace(void __user *user, unsigned int len)
{
        int ret;
        struct ipt_replace tmp;
        struct ipt_table *t;
        struct ipt_table_info *newinfo, *oldinfo;
        struct ipt_counters *counters;

        if (copy_from_user(&tmp, user, sizeof(tmp)) != 0)
                return -EFAULT;

        /* Hack: Causes ipchains to give correct error msg --RR */
        if (len != sizeof(tmp) + tmp.size)
                return -ENOPROTOOPT;

        /* Pedantry: prevent them from hitting BUG() in vmalloc.c --RR */
        if ((SMP_ALIGN(tmp.size) >> PAGE_SHIFT) + 2 > num_physpages)
                return -ENOMEM;

        newinfo = vmalloc(sizeof(struct ipt_table_info)
                          + SMP_ALIGN(tmp.size) * num_possible_cpus());
        if (!newinfo)
                return -ENOMEM;

        if (copy_from_user(newinfo->entries, user + sizeof(tmp),
                           tmp.size) != 0) {
                ret = -EFAULT;
                goto free_newinfo;
        }

        counters = vmalloc(tmp.num_counters * sizeof(struct ipt_counters));
        if (!counters) {
                ret = -ENOMEM;
                goto free_newinfo;
        }
        memset(counters, 0, tmp.num_counters * sizeof(struct ipt_counters));

        ret = translate_table(tmp.name, tmp.valid_hooks,
                              newinfo, tmp.size, tmp.num_entries,
                              tmp.hook_entry, tmp.underflow);
        if (ret != 0)
                goto free_newinfo_counters;

        duprintf("ip_tables: Translated table\n");

        t = try_then_request_module(find_table_lock(tmp.name),
                                    "iptable_%s", tmp.name);
        if (!t || IS_ERR(t)) {
                ret = t ? PTR_ERR(t) : -ENOENT;
                goto free_newinfo_counters_untrans;
        }

        /* You lied! */
        if (tmp.valid_hooks != t->valid_hooks) {
                duprintf("Valid hook crap: %08X vs %08X\n",
                         tmp.valid_hooks, t->valid_hooks);
                ret = -EINVAL;
                goto put_module;
        }

        oldinfo = replace_table(t, tmp.num_counters, newinfo, &ret);
        if (!oldinfo)
                goto put_module;

        /* Update module usage count based on number of rules */
        duprintf("do_replace: oldnum=%u, initnum=%u, newnum=%u\n",
                oldinfo->number, oldinfo->initial_entries, newinfo->number);
        if ((oldinfo->number > oldinfo->initial_entries) || 
            (newinfo->number <= oldinfo->initial_entries)) 
                module_put(t->me);
        if ((oldinfo->number > oldinfo->initial_entries) &&
            (newinfo->number <= oldinfo->initial_entries))
                module_put(t->me);

        /* Get the old counters. */
        get_counters(oldinfo, counters);
        /* Decrease module usage counts and free resource */
        IPT_ENTRY_ITERATE(oldinfo->entries, oldinfo->size, cleanup_entry,NULL);
        vfree(oldinfo);
        if (copy_to_user(tmp.counters, counters,
                         sizeof(struct ipt_counters) * tmp.num_counters) != 0)
                ret = -EFAULT;
        vfree(counters);
        up(&ipt_mutex);
        return ret;

 put_module:
        module_put(t->me);
        up(&ipt_mutex);
 free_newinfo_counters_untrans:
        IPT_ENTRY_ITERATE(newinfo->entries, newinfo->size, cleanup_entry,NULL);
 free_newinfo_counters:
        vfree(counters);
 free_newinfo:
        vfree(newinfo);
        return ret;
}

/* We're lazy, and add to the first CPU; overflow works its fey magic
 * and everything is OK. */
static inline int
add_counter_to_entry(struct ipt_entry *e,
                     const struct ipt_counters addme[],
                     unsigned int *i)
{
#if 0
        duprintf("add_counter: Entry %u %lu/%lu + %lu/%lu\n",
                 *i,
                 (long unsigned int)e->counters.pcnt,
                 (long unsigned int)e->counters.bcnt,
                 (long unsigned int)addme[*i].pcnt,
                 (long unsigned int)addme[*i].bcnt);
#endif

        ADD_COUNTER(e->counters, addme[*i].bcnt, addme[*i].pcnt);

        (*i)++;
        return 0;
}

static int
do_add_counters(void __user *user, unsigned int len)
{
        unsigned int i;
        struct ipt_counters_info tmp, *paddc;
        struct ipt_table *t;
        int ret = 0;

        if (copy_from_user(&tmp, user, sizeof(tmp)) != 0)
                return -EFAULT;

        if (len != sizeof(tmp) + tmp.num_counters*sizeof(struct ipt_counters))
                return -EINVAL;

        paddc = vmalloc(len);
        if (!paddc)
                return -ENOMEM;

        if (copy_from_user(paddc, user, len) != 0) {
                ret = -EFAULT;
                goto free;
        }

        t = find_table_lock(tmp.name);
        if (!t || IS_ERR(t)) {
                ret = t ? PTR_ERR(t) : -ENOENT;
                goto free;
        }

        write_lock_bh(&t->lock);
        if (t->private->number != paddc->num_counters) {
                ret = -EINVAL;
                goto unlock_up_free;
        }

        i = 0;
        IPT_ENTRY_ITERATE(t->private->entries,
                          t->private->size,
                          add_counter_to_entry,
                          paddc->counters,
                          &i);
 unlock_up_free:
        write_unlock_bh(&t->lock);
        up(&ipt_mutex);
        module_put(t->me);
 free:
        vfree(paddc);

        return ret;
}

static int
do_ipt_set_ctl(struct sock *sk, int cmd, void __user *user, unsigned int len)
{
        int ret;

        if (!capable(CAP_NET_ADMIN))
                return -EPERM;

        switch (cmd) {
        case IPT_SO_SET_REPLACE:
                ret = do_replace(user, len);
                break;

        case IPT_SO_SET_ADD_COUNTERS:
                ret = do_add_counters(user, len);
                break;

        default:
                duprintf("do_ipt_set_ctl:  unknown request %i\n", cmd);
                ret = -EINVAL;
        }

        return ret;
}

static int
do_ipt_get_ctl(struct sock *sk, int cmd, void __user *user, int *len)
{
        int ret;

        if (!capable(CAP_NET_ADMIN))
                return -EPERM;

        switch (cmd) {
        case IPT_SO_GET_INFO: {
                char name[IPT_TABLE_MAXNAMELEN];
                struct ipt_table *t;

                if (*len != sizeof(struct ipt_getinfo)) {
                        duprintf("length %u != %u\n", *len,
                                 sizeof(struct ipt_getinfo));
                        ret = -EINVAL;
                        break;
                }

                if (copy_from_user(name, user, sizeof(name)) != 0) {
                        ret = -EFAULT;
                        break;
                }
                name[IPT_TABLE_MAXNAMELEN-1] = '\0';

                t = try_then_request_module(find_table_lock(name),
                                            "iptable_%s", name);
                if (t && !IS_ERR(t)) {
                        struct ipt_getinfo info;

                        info.valid_hooks = t->valid_hooks;
                        memcpy(info.hook_entry, t->private->hook_entry,
                               sizeof(info.hook_entry));
                        memcpy(info.underflow, t->private->underflow,
                               sizeof(info.underflow));
                        info.num_entries = t->private->number;
                        info.size = t->private->size;
                        memcpy(info.name, name, sizeof(info.name));

                        if (copy_to_user(user, &info, *len) != 0)
                                ret = -EFAULT;
                        else
                                ret = 0;
                        up(&ipt_mutex);
                        module_put(t->me);
                } else
                        ret = t ? PTR_ERR(t) : -ENOENT;
        }
        break;

        case IPT_SO_GET_ENTRIES: {
                struct ipt_get_entries get;

                if (*len < sizeof(get)) {
                        duprintf("get_entries: %u < %u\n", *len, sizeof(get));
                        ret = -EINVAL;
                } else if (copy_from_user(&get, user, sizeof(get)) != 0) {
                        ret = -EFAULT;
                } else if (*len != sizeof(struct ipt_get_entries) + get.size) {
                        duprintf("get_entries: %u != %u\n", *len,
                                 sizeof(struct ipt_get_entries) + get.size);
                        ret = -EINVAL;
                } else
                        ret = get_entries(&get, user);
                break;
        }

        case IPT_SO_GET_REVISION_MATCH:
        case IPT_SO_GET_REVISION_TARGET: {
                struct ipt_get_revision rev;
                int (*revfn)(const char *, u8, int *);

                if (*len != sizeof(rev)) {
                        ret = -EINVAL;
                        break;
                }
                if (copy_from_user(&rev, user, sizeof(rev)) != 0) {
                        ret = -EFAULT;
                        break;
                }

                if (cmd == IPT_SO_GET_REVISION_TARGET)
                        revfn = target_revfn;
                else
                        revfn = match_revfn;

                try_then_request_module(find_revision(rev.name, rev.revision,
                                                      revfn, &ret),
                                        "ipt_%s", rev.name);
                break;
        }

        default:
                duprintf("do_ipt_get_ctl: unknown request %i\n", cmd);
                ret = -EINVAL;
        }

        return ret;
}

/* Registration hooks for targets. */
int
ipt_register_target(struct ipt_target *target)
{
        int ret;

        ret = down_interruptible(&ipt_mutex);
        if (ret != 0)
                return ret;
        list_add(&target->list, &ipt_target);
        up(&ipt_mutex);
        return ret;
}

void
ipt_unregister_target(struct ipt_target *target)
{
        down(&ipt_mutex);
        LIST_DELETE(&ipt_target, target);
        up(&ipt_mutex);
}

int
ipt_register_match(struct ipt_match *match)
{
        int ret;

        ret = down_interruptible(&ipt_mutex);
        if (ret != 0)
                return ret;

        list_add(&match->list, &ipt_match);
        up(&ipt_mutex);

        return ret;
}

void
ipt_unregister_match(struct ipt_match *match)
{
        down(&ipt_mutex);
        LIST_DELETE(&ipt_match, match);
        up(&ipt_mutex);
}

int ipt_register_table(struct ipt_table *table, const struct ipt_replace *repl)
{
        int ret;
        struct ipt_table_info *newinfo;
        static struct ipt_table_info bootstrap
                = { 0, 0, 0, { 0 }, { 0 }, { } };

        newinfo = vmalloc(sizeof(struct ipt_table_info)
                          + SMP_ALIGN(repl->size) * num_possible_cpus());
        if (!newinfo)
                return -ENOMEM;

        memcpy(newinfo->entries, repl->entries, repl->size);

        ret = translate_table(table->name, table->valid_hooks,
                              newinfo, repl->size,
                              repl->num_entries,
                              repl->hook_entry,
                              repl->underflow);
        if (ret != 0) {
                vfree(newinfo);
                return ret;
        }

        ret = down_interruptible(&ipt_mutex);
        if (ret != 0) {
                vfree(newinfo);
                return ret;
        }

        /* Don't autoload: we'd eat our tail... */
        if (list_named_find(&ipt_tables, table->name)) {
                ret = -EEXIST;
                goto free_unlock;
        }

        /* Simplifies replace_table code. */
        table->private = &bootstrap;
        if (!replace_table(table, 0, newinfo, &ret))
                goto free_unlock;

        duprintf("table->private->number = %u\n",
                 table->private->number);
        
        /* save number of initial entries */
        table->private->initial_entries = table->private->number;

        rwlock_init(&table->lock);
        list_prepend(&ipt_tables, table);

 unlock:
        up(&ipt_mutex);
        return ret;

 free_unlock:
        vfree(newinfo);
        goto unlock;
}

void ipt_unregister_table(struct ipt_table *table)
{
        down(&ipt_mutex);
        LIST_DELETE(&ipt_tables, table);
        up(&ipt_mutex);

        /* Decrease module usage counts and free resources */
        IPT_ENTRY_ITERATE(table->private->entries, table->private->size,
                          cleanup_entry, NULL);
        vfree(table->private);
}

/* Returns 1 if the port is matched by the range, 0 otherwise */
static inline int
port_match(u_int16_t min, u_int16_t max, u_int16_t port, int invert)
{
        int ret;

        ret = (port >= min && port <= max) ^ invert;
        return ret;
}

static int
tcp_find_option(u_int8_t option,
                const struct sk_buff *skb,
                unsigned int optlen,
                int invert,
                int *hotdrop)
{
        /* tcp.doff is only 4 bits, ie. max 15 * 4 bytes */
        u_int8_t _opt[60 - sizeof(struct tcphdr)], *op;
        unsigned int i;

        duprintf("tcp_match: finding option\n");

        if (!optlen)
                return invert;

        /* If we don't have the whole header, drop packet. */
        op = skb_header_pointer(skb,
                                skb->nh.iph->ihl*4 + sizeof(struct tcphdr),
                                optlen, _opt);
        if (op == NULL) {
                *hotdrop = 1;
                return 0;
        }

        for (i = 0; i < optlen; ) {
                if (op[i] == option) return !invert;
                if (op[i] < 2) i++;
                else i += op[i+1]?:1;
        }

        return invert;
}

static int
tcp_match(const struct sk_buff *skb,
          const struct net_device *in,
          const struct net_device *out,
          const void *matchinfo,
          int offset,
          int *hotdrop)
{
        struct tcphdr _tcph, *th;
        const struct ipt_tcp *tcpinfo = matchinfo;

        if (offset) {
                /* To quote Alan:

                   Don't allow a fragment of TCP 8 bytes in. Nobody normal
                   causes this. Its a cracker trying to break in by doing a
                   flag overwrite to pass the direction checks.
                */
                if (offset == 1) {
                        duprintf("Dropping evil TCP offset=1 frag.\n");
                        *hotdrop = 1;
                }
                /* Must not be a fragment. */
                return 0;
        }

#define FWINVTCP(bool,invflg) ((bool) ^ !!(tcpinfo->invflags & invflg))

        th = skb_header_pointer(skb, skb->nh.iph->ihl*4,
                                sizeof(_tcph), &_tcph);
        if (th == NULL) {
                /* We've been asked to examine this packet, and we
                   can't.  Hence, no choice but to drop. */
                duprintf("Dropping evil TCP offset=0 tinygram.\n");
                *hotdrop = 1;
                return 0;
        }

        if (!port_match(tcpinfo->spts[0], tcpinfo->spts[1],
                        ntohs(th->source),
                        !!(tcpinfo->invflags & IPT_TCP_INV_SRCPT)))
                return 0;
        if (!port_match(tcpinfo->dpts[0], tcpinfo->dpts[1],
                        ntohs(th->dest),
                        !!(tcpinfo->invflags & IPT_TCP_INV_DSTPT)))
                return 0;
        if (!FWINVTCP((((unsigned char *)th)[13] & tcpinfo->flg_mask)
                      == tcpinfo->flg_cmp,
                      IPT_TCP_INV_FLAGS))
                return 0;
        if (tcpinfo->option) {
                if (th->doff * 4 < sizeof(_tcph)) {
                        *hotdrop = 1;
                        return 0;
                }
                if (!tcp_find_option(tcpinfo->option, skb,
                                     th->doff*4 - sizeof(_tcph),
                                     tcpinfo->invflags & IPT_TCP_INV_OPTION,
                                     hotdrop))
                        return 0;
        }
        return 1;
}

/* Called when user tries to insert an entry of this type. */
static int
tcp_checkentry(const char *tablename,
               const struct ipt_ip *ip,
               void *matchinfo,
               unsigned int matchsize,
               unsigned int hook_mask)
{
        const struct ipt_tcp *tcpinfo = matchinfo;

        /* Must specify proto == TCP, and no unknown invflags */
        return ip->proto == IPPROTO_TCP
                && !(ip->invflags & IPT_INV_PROTO)
                && matchsize == IPT_ALIGN(sizeof(struct ipt_tcp))
                && !(tcpinfo->invflags & ~IPT_TCP_INV_MASK);
}

static int
udp_match(const struct sk_buff *skb,
          const struct net_device *in,
          const struct net_device *out,
          const void *matchinfo,
          int offset,
          int *hotdrop)
{
        struct udphdr _udph, *uh;
        const struct ipt_udp *udpinfo = matchinfo;

        /* Must not be a fragment. */
        if (offset)
                return 0;

        uh = skb_header_pointer(skb, skb->nh.iph->ihl*4,
                                sizeof(_udph), &_udph);
        if (uh == NULL) {
                /* We've been asked to examine this packet, and we
                   can't.  Hence, no choice but to drop. */
                duprintf("Dropping evil UDP tinygram.\n");
                *hotdrop = 1;
                return 0;
        }

        return port_match(udpinfo->spts[0], udpinfo->spts[1],
                          ntohs(uh->source),
                          !!(udpinfo->invflags & IPT_UDP_INV_SRCPT))
                && port_match(udpinfo->dpts[0], udpinfo->dpts[1],
                              ntohs(uh->dest),
                              !!(udpinfo->invflags & IPT_UDP_INV_DSTPT));
}

/* Called when user tries to insert an entry of this type. */
static int
udp_checkentry(const char *tablename,
               const struct ipt_ip *ip,
               void *matchinfo,
               unsigned int matchinfosize,
               unsigned int hook_mask)
{
        const struct ipt_udp *udpinfo = matchinfo;

        /* Must specify proto == UDP, and no unknown invflags */
        if (ip->proto != IPPROTO_UDP || (ip->invflags & IPT_INV_PROTO)) {
                duprintf("ipt_udp: Protocol %u != %u\n", ip->proto,
                         IPPROTO_UDP);
                return 0;
        }
        if (matchinfosize != IPT_ALIGN(sizeof(struct ipt_udp))) {
                duprintf("ipt_udp: matchsize %u != %u\n",
                         matchinfosize, IPT_ALIGN(sizeof(struct ipt_udp)));
                return 0;
        }
        if (udpinfo->invflags & ~IPT_UDP_INV_MASK) {
                duprintf("ipt_udp: unknown flags %X\n",
                         udpinfo->invflags);
                return 0;
        }

        return 1;
}

/* Returns 1 if the type and code is matched by the range, 0 otherwise */
static inline int
icmp_type_code_match(u_int8_t test_type, u_int8_t min_code, u_int8_t max_code,
                     u_int8_t type, u_int8_t code,
                     int invert)
{
        return ((test_type == 0xFF) || (type == test_type && code >= min_code && code <= max_code))
                ^ invert;
}

static int
icmp_match(const struct sk_buff *skb,
           const struct net_device *in,
           const struct net_device *out,
           const void *matchinfo,
           int offset,
           int *hotdrop)
{
        struct icmphdr _icmph, *ic;
        const struct ipt_icmp *icmpinfo = matchinfo;

        /* Must not be a fragment. */
        if (offset)
                return 0;

        ic = skb_header_pointer(skb, skb->nh.iph->ihl*4,
                                sizeof(_icmph), &_icmph);
        if (ic == NULL) {
                /* We've been asked to examine this packet, and we
                 * can't.  Hence, no choice but to drop.
                 */
                duprintf("Dropping evil ICMP tinygram.\n");
                *hotdrop = 1;
                return 0;
        }

        return icmp_type_code_match(icmpinfo->type,
                                    icmpinfo->code[0],
                                    icmpinfo->code[1],
                                    ic->type, ic->code,
                                    !!(icmpinfo->invflags&IPT_ICMP_INV));
}

/* Called when user tries to insert an entry of this type. */
static int
icmp_checkentry(const char *tablename,
           const struct ipt_ip *ip,
           void *matchinfo,
           unsigned int matchsize,
           unsigned int hook_mask)
{
        const struct ipt_icmp *icmpinfo = matchinfo;

        /* Must specify proto == ICMP, and no unknown invflags */
        return ip->proto == IPPROTO_ICMP
                && !(ip->invflags & IPT_INV_PROTO)
                && matchsize == IPT_ALIGN(sizeof(struct ipt_icmp))
                && !(icmpinfo->invflags & ~IPT_ICMP_INV);
}

/* The built-in targets: standard (NULL) and error. */
static struct ipt_target ipt_standard_target = {
        .name           = IPT_STANDARD_TARGET,
};

static struct ipt_target ipt_error_target = {
        .name           = IPT_ERROR_TARGET,
        .target         = ipt_error,
};

static struct nf_sockopt_ops ipt_sockopts = {
        .pf             = PF_INET,
        .set_optmin     = IPT_BASE_CTL,
        .set_optmax     = IPT_SO_SET_MAX+1,
        .set            = do_ipt_set_ctl,
        .get_optmin     = IPT_BASE_CTL,
        .get_optmax     = IPT_SO_GET_MAX+1,
        .get            = do_ipt_get_ctl,
};

static struct ipt_match tcp_matchstruct = {
        .name           = "tcp",
        .match          = &tcp_match,
        .checkentry     = &tcp_checkentry,
};

static struct ipt_match udp_matchstruct = {
        .name           = "udp",
        .match          = &udp_match,
        .checkentry     = &udp_checkentry,
};

static struct ipt_match icmp_matchstruct = {
        .name           = "icmp",
        .match          = &icmp_match,
        .checkentry     = &icmp_checkentry,
};

#ifdef CONFIG_PROC_FS
static inline int print_name(const char *i,
                             off_t start_offset, char *buffer, int length,
                             off_t *pos, unsigned int *count)
{
        if ((*count)++ >= start_offset) {
                unsigned int namelen;

                namelen = sprintf(buffer + *pos, "%s\n",
                                  i + sizeof(struct list_head));
                if (*pos + namelen > length) {
                        /* Stop iterating */
                        return 1;
                }
                *pos += namelen;
        }
        return 0;
}

static inline int print_target(const struct ipt_target *t,
                               off_t start_offset, char *buffer, int length,
                               off_t *pos, unsigned int *count)
{
        if (t == &ipt_standard_target || t == &ipt_error_target)
                return 0;
        return print_name((char *)t, start_offset, buffer, length, pos, count);
}

static int ipt_get_tables(char *buffer, char **start, off_t offset, int length)
{
        off_t pos = 0;
        unsigned int count = 0;

        if (down_interruptible(&ipt_mutex) != 0)
                return 0;

        LIST_FIND(&ipt_tables, print_name, void *,
                  offset, buffer, length, &pos, &count);

        up(&ipt_mutex);

        /* `start' hack - see fs/proc/generic.c line ~105 */
        *start=(char *)((unsigned long)count-offset);
        return pos;
}

static int ipt_get_targets(char *buffer, char **start, off_t offset, int length)
{
        off_t pos = 0;
        unsigned int count = 0;

        if (down_interruptible(&ipt_mutex) != 0)
                return 0;

        LIST_FIND(&ipt_target, print_target, struct ipt_target *,
                  offset, buffer, length, &pos, &count);
        
        up(&ipt_mutex);

        *start = (char *)((unsigned long)count - offset);
        return pos;
}

static int ipt_get_matches(char *buffer, char **start, off_t offset, int length)
{
        off_t pos = 0;
        unsigned int count = 0;

        if (down_interruptible(&ipt_mutex) != 0)
                return 0;
        
        LIST_FIND(&ipt_match, print_name, void *,
                  offset, buffer, length, &pos, &count);

        up(&ipt_mutex);

        *start = (char *)((unsigned long)count - offset);
        return pos;
}

static struct { char *name; get_info_t *get_info; } ipt_proc_entry[] =
{ { "ip_tables_names", ipt_get_tables },
  { "ip_tables_targets", ipt_get_targets },
  { "ip_tables_matches", ipt_get_matches },
  { NULL, NULL} };
#endif /*CONFIG_PROC_FS*/

static int __init init(void)
{
        int ret;

        /* Noone else will be downing sem now, so we won't sleep */
        down(&ipt_mutex);
        list_append(&ipt_target, &ipt_standard_target);
        list_append(&ipt_target, &ipt_error_target);
        list_append(&ipt_match, &tcp_matchstruct);
        list_append(&ipt_match, &udp_matchstruct);
        list_append(&ipt_match, &icmp_matchstruct);
        up(&ipt_mutex);

        /* Register setsockopt */
        ret = nf_register_sockopt(&ipt_sockopts);
        if (ret < 0) {
                duprintf("Unable to register sockopts.\n");
                return ret;
        }

#ifdef CONFIG_PROC_FS
        {
        struct proc_dir_entry *proc;
        int i;

        for (i = 0; ipt_proc_entry[i].name; i++) {
                proc = proc_net_create(ipt_proc_entry[i].name, 0,
                                       ipt_proc_entry[i].get_info);
                if (!proc) {
                        while (--i >= 0)
                                proc_net_remove(ipt_proc_entry[i].name);
                        nf_unregister_sockopt(&ipt_sockopts);
                        return -ENOMEM;
                }
                proc->owner = THIS_MODULE;
        }
        }
#endif

        printk("ip_tables: (C) 2000-2002 Netfilter core team\n");
        return 0;
}

static void __exit fini(void)
{
        nf_unregister_sockopt(&ipt_sockopts);
#ifdef CONFIG_PROC_FS
        {
        int i;
        for (i = 0; ipt_proc_entry[i].name; i++)
                proc_net_remove(ipt_proc_entry[i].name);
        }
#endif
}

EXPORT_SYMBOL(ipt_register_table);
EXPORT_SYMBOL(ipt_unregister_table);
EXPORT_SYMBOL(ipt_register_match);
EXPORT_SYMBOL(ipt_unregister_match);
EXPORT_SYMBOL(ipt_do_table);
EXPORT_SYMBOL(ipt_register_target);
EXPORT_SYMBOL(ipt_unregister_target);
EXPORT_SYMBOL(ipt_find_target);

module_init(init);
module_exit(fini);