[NETFILTER]: ip_conntrack: properly use RCU for ip_conntrack_destroyed callback

[linux-2.6.22.y-op.git] / net / ipv4 / netfilter / ip_nat_core.c

/* NAT for netfilter; shared with compatibility layer. */

/* (C) 1999-2001 Paul `Rusty' Russell
 * (C) 2002-2004 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.
 */

#include <linux/module.h>
#include <linux/types.h>
#include <linux/timer.h>
#include <linux/skbuff.h>
#include <linux/netfilter_ipv4.h>
#include <linux/vmalloc.h>
#include <net/checksum.h>
#include <net/icmp.h>
#include <net/ip.h>
#include <net/tcp.h>  /* For tcp_prot in getorigdst */
#include <linux/icmp.h>
#include <linux/udp.h>
#include <linux/jhash.h>

#include <linux/netfilter_ipv4/ip_conntrack.h>
#include <linux/netfilter_ipv4/ip_conntrack_core.h>
#include <linux/netfilter_ipv4/ip_conntrack_protocol.h>
#include <linux/netfilter_ipv4/ip_nat.h>
#include <linux/netfilter_ipv4/ip_nat_protocol.h>
#include <linux/netfilter_ipv4/ip_nat_core.h>
#include <linux/netfilter_ipv4/ip_nat_helper.h>
#include <linux/netfilter_ipv4/ip_conntrack_helper.h>

#if 0
#define DEBUGP printk
#else
#define DEBUGP(format, args...)
#endif

DEFINE_RWLOCK(ip_nat_lock);

/* Calculated at init based on memory size */
static unsigned int ip_nat_htable_size;

static struct list_head *bysource;

#define MAX_IP_NAT_PROTO 256
static struct ip_nat_protocol *ip_nat_protos[MAX_IP_NAT_PROTO];

static inline struct ip_nat_protocol *
__ip_nat_proto_find(u_int8_t protonum)
{
        return rcu_dereference(ip_nat_protos[protonum]);
}

struct ip_nat_protocol *
ip_nat_proto_find_get(u_int8_t protonum)
{
        struct ip_nat_protocol *p;

        rcu_read_lock();
        p = __ip_nat_proto_find(protonum);
        if (!try_module_get(p->me))
                p = &ip_nat_unknown_protocol;
        rcu_read_unlock();

        return p;
}
EXPORT_SYMBOL_GPL(ip_nat_proto_find_get);

void
ip_nat_proto_put(struct ip_nat_protocol *p)
{
        module_put(p->me);
}
EXPORT_SYMBOL_GPL(ip_nat_proto_put);

/* We keep an extra hash for each conntrack, for fast searching. */
static inline unsigned int
hash_by_src(const struct ip_conntrack_tuple *tuple)
{
        /* Original src, to ensure we map it consistently if poss. */
        return jhash_3words((__force u32)tuple->src.ip, tuple->src.u.all,
                            tuple->dst.protonum, 0) % ip_nat_htable_size;
}

/* Noone using conntrack by the time this called. */
static void ip_nat_cleanup_conntrack(struct ip_conntrack *conn)
{
        if (!(conn->status & IPS_NAT_DONE_MASK))
                return;

        write_lock_bh(&ip_nat_lock);
        list_del(&conn->nat.info.bysource);
        write_unlock_bh(&ip_nat_lock);
}

/* Is this tuple already taken? (not by us) */
int
ip_nat_used_tuple(const struct ip_conntrack_tuple *tuple,
                  const struct ip_conntrack *ignored_conntrack)
{
        /* Conntrack tracking doesn't keep track of outgoing tuples; only
           incoming ones.  NAT means they don't have a fixed mapping,
           so we invert the tuple and look for the incoming reply.

           We could keep a separate hash if this proves too slow. */
        struct ip_conntrack_tuple reply;

        invert_tuplepr(&reply, tuple);
        return ip_conntrack_tuple_taken(&reply, ignored_conntrack);
}
EXPORT_SYMBOL(ip_nat_used_tuple);

/* If we source map this tuple so reply looks like reply_tuple, will
 * that meet the constraints of range. */
static int
in_range(const struct ip_conntrack_tuple *tuple,
         const struct ip_nat_range *range)
{
        struct ip_nat_protocol *proto;
        int ret = 0;

        /* If we are supposed to map IPs, then we must be in the
           range specified, otherwise let this drag us onto a new src IP. */
        if (range->flags & IP_NAT_RANGE_MAP_IPS) {
                if (ntohl(tuple->src.ip) < ntohl(range->min_ip)
                    || ntohl(tuple->src.ip) > ntohl(range->max_ip))
                        return 0;
        }

        rcu_read_lock();
        proto = __ip_nat_proto_find(tuple->dst.protonum);
        if (!(range->flags & IP_NAT_RANGE_PROTO_SPECIFIED)
            || proto->in_range(tuple, IP_NAT_MANIP_SRC,
                               &range->min, &range->max))
                ret = 1;
        rcu_read_unlock();

        return ret;
}

static inline int
same_src(const struct ip_conntrack *ct,
         const struct ip_conntrack_tuple *tuple)
{
        return (ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.dst.protonum
                == tuple->dst.protonum
                && ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.src.ip
                == tuple->src.ip
                && ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.src.u.all
                == tuple->src.u.all);
}

/* Only called for SRC manip */
static int
find_appropriate_src(const struct ip_conntrack_tuple *tuple,
                     struct ip_conntrack_tuple *result,
                     const struct ip_nat_range *range)
{
        unsigned int h = hash_by_src(tuple);
        struct ip_conntrack *ct;

        read_lock_bh(&ip_nat_lock);
        list_for_each_entry(ct, &bysource[h], nat.info.bysource) {
                if (same_src(ct, tuple)) {
                        /* Copy source part from reply tuple. */
                        invert_tuplepr(result,
                                       &ct->tuplehash[IP_CT_DIR_REPLY].tuple);
                        result->dst = tuple->dst;

                        if (in_range(result, range)) {
                                read_unlock_bh(&ip_nat_lock);
                                return 1;
                        }
                }
        }
        read_unlock_bh(&ip_nat_lock);
        return 0;
}

/* For [FUTURE] fragmentation handling, we want the least-used
   src-ip/dst-ip/proto triple.  Fairness doesn't come into it.  Thus
   if the range specifies 1.2.3.4 ports 10000-10005 and 1.2.3.5 ports
   1-65535, we don't do pro-rata allocation based on ports; we choose
   the ip with the lowest src-ip/dst-ip/proto usage.
*/
static void
find_best_ips_proto(struct ip_conntrack_tuple *tuple,
                    const struct ip_nat_range *range,
                    const struct ip_conntrack *conntrack,
                    enum ip_nat_manip_type maniptype)
{
        __be32 *var_ipp;
        /* Host order */
        u_int32_t minip, maxip, j;

        /* No IP mapping?  Do nothing. */
        if (!(range->flags & IP_NAT_RANGE_MAP_IPS))
                return;

        if (maniptype == IP_NAT_MANIP_SRC)
                var_ipp = &tuple->src.ip;
        else
                var_ipp = &tuple->dst.ip;

        /* Fast path: only one choice. */
        if (range->min_ip == range->max_ip) {
                *var_ipp = range->min_ip;
                return;
        }

        /* Hashing source and destination IPs gives a fairly even
         * spread in practice (if there are a small number of IPs
         * involved, there usually aren't that many connections
         * anyway).  The consistency means that servers see the same
         * client coming from the same IP (some Internet Banking sites
         * like this), even across reboots. */
        minip = ntohl(range->min_ip);
        maxip = ntohl(range->max_ip);
        j = jhash_2words((__force u32)tuple->src.ip, (__force u32)tuple->dst.ip, 0);
        *var_ipp = htonl(minip + j % (maxip - minip + 1));
}

/* Manipulate the tuple into the range given.  For NF_IP_POST_ROUTING,
 * we change the source to map into the range.  For NF_IP_PRE_ROUTING
 * and NF_IP_LOCAL_OUT, we change the destination to map into the
 * range.  It might not be possible to get a unique tuple, but we try.
 * At worst (or if we race), we will end up with a final duplicate in
 * __ip_conntrack_confirm and drop the packet. */
static void
get_unique_tuple(struct ip_conntrack_tuple *tuple,
                 const struct ip_conntrack_tuple *orig_tuple,
                 const struct ip_nat_range *range,
                 struct ip_conntrack *conntrack,
                 enum ip_nat_manip_type maniptype)
{
        struct ip_nat_protocol *proto;

        /* 1) If this srcip/proto/src-proto-part is currently mapped,
           and that same mapping gives a unique tuple within the given
           range, use that.

           This is only required for source (ie. NAT/masq) mappings.
           So far, we don't do local source mappings, so multiple
           manips not an issue.  */
        if (maniptype == IP_NAT_MANIP_SRC) {
                if (find_appropriate_src(orig_tuple, tuple, range)) {
                        DEBUGP("get_unique_tuple: Found current src map\n");
                        if (!(range->flags & IP_NAT_RANGE_PROTO_RANDOM))
                                if (!ip_nat_used_tuple(tuple, conntrack))
                                        return;
                }
        }

        /* 2) Select the least-used IP/proto combination in the given
           range. */
        *tuple = *orig_tuple;
        find_best_ips_proto(tuple, range, conntrack, maniptype);

        /* 3) The per-protocol part of the manip is made to map into
           the range to make a unique tuple. */

        rcu_read_lock();
        proto = __ip_nat_proto_find(orig_tuple->dst.protonum);

        /* Change protocol info to have some randomization */
        if (range->flags & IP_NAT_RANGE_PROTO_RANDOM) {
                proto->unique_tuple(tuple, range, maniptype, conntrack);
                goto out;
        }

        /* Only bother mapping if it's not already in range and unique */
        if ((!(range->flags & IP_NAT_RANGE_PROTO_SPECIFIED)
             || proto->in_range(tuple, maniptype, &range->min, &range->max))
            && !ip_nat_used_tuple(tuple, conntrack))
                goto out;

        /* Last change: get protocol to try to obtain unique tuple. */
        proto->unique_tuple(tuple, range, maniptype, conntrack);
out:
        rcu_read_unlock();
}

unsigned int
ip_nat_setup_info(struct ip_conntrack *conntrack,
                  const struct ip_nat_range *range,
                  unsigned int hooknum)
{
        struct ip_conntrack_tuple curr_tuple, new_tuple;
        struct ip_nat_info *info = &conntrack->nat.info;
        int have_to_hash = !(conntrack->status & IPS_NAT_DONE_MASK);
        enum ip_nat_manip_type maniptype = HOOK2MANIP(hooknum);

        IP_NF_ASSERT(hooknum == NF_IP_PRE_ROUTING
                     || hooknum == NF_IP_POST_ROUTING
                     || hooknum == NF_IP_LOCAL_IN
                     || hooknum == NF_IP_LOCAL_OUT);
        BUG_ON(ip_nat_initialized(conntrack, maniptype));

        /* What we've got will look like inverse of reply. Normally
           this is what is in the conntrack, except for prior
           manipulations (future optimization: if num_manips == 0,
           orig_tp =
           conntrack->tuplehash[IP_CT_DIR_ORIGINAL].tuple) */
        invert_tuplepr(&curr_tuple,
                       &conntrack->tuplehash[IP_CT_DIR_REPLY].tuple);

        get_unique_tuple(&new_tuple, &curr_tuple, range, conntrack, maniptype);

        if (!ip_ct_tuple_equal(&new_tuple, &curr_tuple)) {
                struct ip_conntrack_tuple reply;

                /* Alter conntrack table so will recognize replies. */
                invert_tuplepr(&reply, &new_tuple);
                ip_conntrack_alter_reply(conntrack, &reply);

                /* Non-atomic: we own this at the moment. */
                if (maniptype == IP_NAT_MANIP_SRC)
                        conntrack->status |= IPS_SRC_NAT;
                else
                        conntrack->status |= IPS_DST_NAT;
        }

        /* Place in source hash if this is the first time. */
        if (have_to_hash) {
                unsigned int srchash
                        = hash_by_src(&conntrack->tuplehash[IP_CT_DIR_ORIGINAL]
                                      .tuple);
                write_lock_bh(&ip_nat_lock);
                list_add(&info->bysource, &bysource[srchash]);
                write_unlock_bh(&ip_nat_lock);
        }

        /* It's done. */
        if (maniptype == IP_NAT_MANIP_DST)
                set_bit(IPS_DST_NAT_DONE_BIT, &conntrack->status);
        else
                set_bit(IPS_SRC_NAT_DONE_BIT, &conntrack->status);

        return NF_ACCEPT;
}
EXPORT_SYMBOL(ip_nat_setup_info);

/* Returns true if succeeded. */
static int
manip_pkt(u_int16_t proto,
          struct sk_buff **pskb,
          unsigned int iphdroff,
          const struct ip_conntrack_tuple *target,
          enum ip_nat_manip_type maniptype)
{
        struct iphdr *iph;
        struct ip_nat_protocol *p;

        if (!skb_make_writable(pskb, iphdroff + sizeof(*iph)))
                return 0;

        iph = (void *)(*pskb)->data + iphdroff;

        /* Manipulate protcol part. */

        /* rcu_read_lock()ed by nf_hook_slow */
        p = __ip_nat_proto_find(proto);
        if (!p->manip_pkt(pskb, iphdroff, target, maniptype))
                return 0;

        iph = (void *)(*pskb)->data + iphdroff;

        if (maniptype == IP_NAT_MANIP_SRC) {
                nf_csum_replace4(&iph->check, iph->saddr, target->src.ip);
                iph->saddr = target->src.ip;
        } else {
                nf_csum_replace4(&iph->check, iph->daddr, target->dst.ip);
                iph->daddr = target->dst.ip;
        }
        return 1;
}

/* Do packet manipulations according to ip_nat_setup_info. */
unsigned int ip_nat_packet(struct ip_conntrack *ct,
                           enum ip_conntrack_info ctinfo,
                           unsigned int hooknum,
                           struct sk_buff **pskb)
{
        enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
        unsigned long statusbit;
        enum ip_nat_manip_type mtype = HOOK2MANIP(hooknum);

        if (mtype == IP_NAT_MANIP_SRC)
                statusbit = IPS_SRC_NAT;
        else
                statusbit = IPS_DST_NAT;

        /* Invert if this is reply dir. */
        if (dir == IP_CT_DIR_REPLY)
                statusbit ^= IPS_NAT_MASK;

        /* Non-atomic: these bits don't change. */
        if (ct->status & statusbit) {
                struct ip_conntrack_tuple target;

                /* We are aiming to look like inverse of other direction. */
                invert_tuplepr(&target, &ct->tuplehash[!dir].tuple);

                if (!manip_pkt(target.dst.protonum, pskb, 0, &target, mtype))
                        return NF_DROP;
        }
        return NF_ACCEPT;
}
EXPORT_SYMBOL_GPL(ip_nat_packet);

/* Dir is direction ICMP is coming from (opposite to packet it contains) */
int ip_nat_icmp_reply_translation(struct ip_conntrack *ct,
                                  enum ip_conntrack_info ctinfo,
                                  unsigned int hooknum,
                                  struct sk_buff **pskb)
{
        struct {
                struct icmphdr icmp;
                struct iphdr ip;
        } *inside;
        struct ip_conntrack_protocol *proto;
        struct ip_conntrack_tuple inner, target;
        int hdrlen = (*pskb)->nh.iph->ihl * 4;
        enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
        unsigned long statusbit;
        enum ip_nat_manip_type manip = HOOK2MANIP(hooknum);

        if (!skb_make_writable(pskb, hdrlen + sizeof(*inside)))
                return 0;

        inside = (void *)(*pskb)->data + (*pskb)->nh.iph->ihl*4;

        /* We're actually going to mangle it beyond trivial checksum
           adjustment, so make sure the current checksum is correct. */
        if (nf_ip_checksum(*pskb, hooknum, hdrlen, 0))
                return 0;

        /* Must be RELATED */
        IP_NF_ASSERT((*pskb)->nfctinfo == IP_CT_RELATED ||
                     (*pskb)->nfctinfo == IP_CT_RELATED+IP_CT_IS_REPLY);

        /* Redirects on non-null nats must be dropped, else they'll
           start talking to each other without our translation, and be
           confused... --RR */
        if (inside->icmp.type == ICMP_REDIRECT) {
                /* If NAT isn't finished, assume it and drop. */
                if ((ct->status & IPS_NAT_DONE_MASK) != IPS_NAT_DONE_MASK)
                        return 0;

                if (ct->status & IPS_NAT_MASK)
                        return 0;
        }

        DEBUGP("icmp_reply_translation: translating error %p manp %u dir %s\n",
               *pskb, manip, dir == IP_CT_DIR_ORIGINAL ? "ORIG" : "REPLY");

        /* rcu_read_lock()ed by nf_hook_slow */
        proto = __ip_conntrack_proto_find(inside->ip.protocol);
        if (!ip_ct_get_tuple(&inside->ip, *pskb, (*pskb)->nh.iph->ihl*4 +
                             sizeof(struct icmphdr) + inside->ip.ihl*4,
                             &inner, proto))
                return 0;

        /* Change inner back to look like incoming packet.  We do the
           opposite manip on this hook to normal, because it might not
           pass all hooks (locally-generated ICMP).  Consider incoming
           packet: PREROUTING (DST manip), routing produces ICMP, goes
           through POSTROUTING (which must correct the DST manip). */
        if (!manip_pkt(inside->ip.protocol, pskb,
                       (*pskb)->nh.iph->ihl*4
                       + sizeof(inside->icmp),
                       &ct->tuplehash[!dir].tuple,
                       !manip))
                return 0;

        if ((*pskb)->ip_summed != CHECKSUM_PARTIAL) {
                /* Reloading "inside" here since manip_pkt inner. */
                inside = (void *)(*pskb)->data + (*pskb)->nh.iph->ihl*4;
                inside->icmp.checksum = 0;
                inside->icmp.checksum = csum_fold(skb_checksum(*pskb, hdrlen,
                                                               (*pskb)->len - hdrlen,
                                                               0));
        }

        /* Change outer to look the reply to an incoming packet
         * (proto 0 means don't invert per-proto part). */
        if (manip == IP_NAT_MANIP_SRC)
                statusbit = IPS_SRC_NAT;
        else
                statusbit = IPS_DST_NAT;

        /* Invert if this is reply dir. */
        if (dir == IP_CT_DIR_REPLY)
                statusbit ^= IPS_NAT_MASK;

        if (ct->status & statusbit) {
                invert_tuplepr(&target, &ct->tuplehash[!dir].tuple);
                if (!manip_pkt(0, pskb, 0, &target, manip))
                        return 0;
        }

        return 1;
}
EXPORT_SYMBOL_GPL(ip_nat_icmp_reply_translation);

/* Protocol registration. */
int ip_nat_protocol_register(struct ip_nat_protocol *proto)
{
        int ret = 0;

        write_lock_bh(&ip_nat_lock);
        if (ip_nat_protos[proto->protonum] != &ip_nat_unknown_protocol) {
                ret = -EBUSY;
                goto out;
        }
        rcu_assign_pointer(ip_nat_protos[proto->protonum], proto);
 out:
        write_unlock_bh(&ip_nat_lock);
        return ret;
}
EXPORT_SYMBOL(ip_nat_protocol_register);

/* Noone stores the protocol anywhere; simply delete it. */
void ip_nat_protocol_unregister(struct ip_nat_protocol *proto)
{
        write_lock_bh(&ip_nat_lock);
        rcu_assign_pointer(ip_nat_protos[proto->protonum],
                           &ip_nat_unknown_protocol);
        write_unlock_bh(&ip_nat_lock);
        synchronize_rcu();
}
EXPORT_SYMBOL(ip_nat_protocol_unregister);

#if defined(CONFIG_IP_NF_CONNTRACK_NETLINK) || \
    defined(CONFIG_IP_NF_CONNTRACK_NETLINK_MODULE)
int
ip_nat_port_range_to_nfattr(struct sk_buff *skb,
                            const struct ip_nat_range *range)
{
        NFA_PUT(skb, CTA_PROTONAT_PORT_MIN, sizeof(__be16),
                &range->min.tcp.port);
        NFA_PUT(skb, CTA_PROTONAT_PORT_MAX, sizeof(__be16),
                &range->max.tcp.port);

        return 0;

nfattr_failure:
        return -1;
}

int
ip_nat_port_nfattr_to_range(struct nfattr *tb[], struct ip_nat_range *range)
{
        int ret = 0;

        /* we have to return whether we actually parsed something or not */

        if (tb[CTA_PROTONAT_PORT_MIN-1]) {
                ret = 1;
                range->min.tcp.port =
                        *(__be16 *)NFA_DATA(tb[CTA_PROTONAT_PORT_MIN-1]);
        }

        if (!tb[CTA_PROTONAT_PORT_MAX-1]) {
                if (ret)
                        range->max.tcp.port = range->min.tcp.port;
        } else {
                ret = 1;
                range->max.tcp.port =
                        *(__be16 *)NFA_DATA(tb[CTA_PROTONAT_PORT_MAX-1]);
        }

        return ret;
}
EXPORT_SYMBOL_GPL(ip_nat_port_nfattr_to_range);
EXPORT_SYMBOL_GPL(ip_nat_port_range_to_nfattr);
#endif

static int __init ip_nat_init(void)
{
        size_t i;

        /* Leave them the same for the moment. */
        ip_nat_htable_size = ip_conntrack_htable_size;

        /* One vmalloc for both hash tables */
        bysource = vmalloc(sizeof(struct list_head) * ip_nat_htable_size);
        if (!bysource)
                return -ENOMEM;

        /* Sew in builtin protocols. */
        write_lock_bh(&ip_nat_lock);
        for (i = 0; i < MAX_IP_NAT_PROTO; i++)
                rcu_assign_pointer(ip_nat_protos[i], &ip_nat_unknown_protocol);
        rcu_assign_pointer(ip_nat_protos[IPPROTO_TCP], &ip_nat_protocol_tcp);
        rcu_assign_pointer(ip_nat_protos[IPPROTO_UDP], &ip_nat_protocol_udp);
        rcu_assign_pointer(ip_nat_protos[IPPROTO_ICMP], &ip_nat_protocol_icmp);
        write_unlock_bh(&ip_nat_lock);

        for (i = 0; i < ip_nat_htable_size; i++) {
                INIT_LIST_HEAD(&bysource[i]);
        }

        /* FIXME: Man, this is a hack.  <SIGH> */
        IP_NF_ASSERT(rcu_dereference(ip_conntrack_destroyed) == NULL);
        rcu_assign_pointer(ip_conntrack_destroyed, ip_nat_cleanup_conntrack);

        /* Initialize fake conntrack so that NAT will skip it */
        ip_conntrack_untracked.status |= IPS_NAT_DONE_MASK;
        return 0;
}

/* Clear NAT section of all conntracks, in case we're loaded again. */
static int clean_nat(struct ip_conntrack *i, void *data)
{
        memset(&i->nat, 0, sizeof(i->nat));
        i->status &= ~(IPS_NAT_MASK | IPS_NAT_DONE_MASK | IPS_SEQ_ADJUST);
        return 0;
}

static void __exit ip_nat_cleanup(void)
{
        ip_ct_iterate_cleanup(&clean_nat, NULL);
        rcu_assign_pointer(ip_conntrack_destroyed, NULL);
        synchronize_rcu();
        vfree(bysource);
}

MODULE_LICENSE("GPL");

module_init(ip_nat_init);
module_exit(ip_nat_cleanup);