// SPDX-License-Identifier: GPL-2.0-or-later

  /*
   * Stateless NAT actions
   *
   * Copyright (c) 2007 Herbert Xu <herbert@gondor.apana.org.au>

   */
  
  #include <linux/errno.h>
  #include <linux/init.h>
  #include <linux/kernel.h>
  #include <linux/module.h>
  #include <linux/netfilter.h>
  #include <linux/rtnetlink.h>
  #include <linux/skbuff.h>
  #include <linux/slab.h>
  #include <linux/spinlock.h>
  #include <linux/string.h>
  #include <linux/tc_act/tc_nat.h>
  #include <net/act_api.h>

  #include <net/pkt_cls.h>

  #include <net/icmp.h>
  #include <net/ip.h>
  #include <net/netlink.h>
  #include <net/tc_act/tc_nat.h>
  #include <net/tcp.h>
  #include <net/udp.h>

  static unsigned int nat_net_id;

  static struct tc_action_ops act_nat_ops;

  static const struct nla_policy nat_policy[TCA_NAT_MAX + 1] = {
  	[TCA_NAT_PARMS]	= { .len = sizeof(struct tc_nat) },
  };

  static int tcf_nat_init(struct net *net, struct nlattr *nla, struct nlattr *est,

  			struct tc_action **a, int ovr, int bind,

  			bool rtnl_held,	struct tcf_proto *tp,

  			u32 flags, struct netlink_ext_ack *extack)

  {

  	struct tc_action_net *tn = net_generic(net, nat_net_id);

  	struct nlattr *tb[TCA_NAT_MAX + 1];

  	struct tcf_chain *goto_ch = NULL;

  	struct tc_nat *parm;

  	int ret = 0, err;

  	struct tcf_nat *p;

  	u32 index;

  	if (nla == NULL)

  		return -EINVAL;

  	err = nla_parse_nested_deprecated(tb, TCA_NAT_MAX, nla, nat_policy,
  					  NULL);

  	if (err < 0)
  		return err;

  	if (tb[TCA_NAT_PARMS] == NULL)

  		return -EINVAL;

  	parm = nla_data(tb[TCA_NAT_PARMS]);

  	index = parm->index;
  	err = tcf_idr_check_alloc(tn, &index, a, bind);

  	if (!err) {

  		ret = tcf_idr_create(tn, index, est, a,

  				     &act_nat_ops, bind, false, 0);

  		if (ret) {

  			tcf_idr_cleanup(tn, index);

  			return ret;

  		}

  		ret = ACT_P_CREATED;

  	} else if (err > 0) {

  		if (bind)
  			return 0;

  		if (!ovr) {
  			tcf_idr_release(*a, bind);

  			return -EEXIST;

  		}

  	} else {
  		return err;

  	}

  	err = tcf_action_check_ctrlact(parm->action, tp, &goto_ch, extack);
  	if (err < 0)
  		goto release_idr;

  	p = to_tcf_nat(*a);

  
  	spin_lock_bh(&p->tcf_lock);
  	p->old_addr = parm->old_addr;
  	p->new_addr = parm->new_addr;
  	p->mask = parm->mask;
  	p->flags = parm->flags;

  	goto_ch = tcf_action_set_ctrlact(*a, parm->action, goto_ch);

  	spin_unlock_bh(&p->tcf_lock);

  	if (goto_ch)
  		tcf_chain_put_by_act(goto_ch);

  	return ret;

  release_idr:
  	tcf_idr_release(*a, bind);
  	return err;

  }

  static int tcf_nat_act(struct sk_buff *skb, const struct tc_action *a,
  		       struct tcf_result *res)

  {

  	struct tcf_nat *p = to_tcf_nat(a);

  	struct iphdr *iph;
  	__be32 old_addr;
  	__be32 new_addr;
  	__be32 mask;
  	__be32 addr;
  	int egress;
  	int action;
  	int ihl;

  	int noff;

  
  	spin_lock(&p->tcf_lock);

  	tcf_lastuse_update(&p->tcf_tm);

  	old_addr = p->old_addr;
  	new_addr = p->new_addr;
  	mask = p->mask;
  	egress = p->flags & TCA_NAT_FLAG_EGRESS;
  	action = p->tcf_action;

  	bstats_update(&p->tcf_bstats, skb);

  
  	spin_unlock(&p->tcf_lock);
  
  	if (unlikely(action == TC_ACT_SHOT))
  		goto drop;

  	noff = skb_network_offset(skb);
  	if (!pskb_may_pull(skb, sizeof(*iph) + noff))

  		goto drop;
  
  	iph = ip_hdr(skb);
  
  	if (egress)
  		addr = iph->saddr;
  	else
  		addr = iph->daddr;
  
  	if (!((old_addr ^ addr) & mask)) {

  		if (skb_try_make_writable(skb, sizeof(*iph) + noff))

  			goto drop;
  
  		new_addr &= mask;
  		new_addr |= addr & ~mask;
  
  		/* Rewrite IP header */
  		iph = ip_hdr(skb);
  		if (egress)
  			iph->saddr = new_addr;
  		else
  			iph->daddr = new_addr;

  		csum_replace4(&iph->check, addr, new_addr);

  	} else if ((iph->frag_off & htons(IP_OFFSET)) ||
  		   iph->protocol != IPPROTO_ICMP) {
  		goto out;

  	}
  
  	ihl = iph->ihl * 4;
  
  	/* It would be nice to share code with stateful NAT. */
  	switch (iph->frag_off & htons(IP_OFFSET) ? 0 : iph->protocol) {
  	case IPPROTO_TCP:
  	{
  		struct tcphdr *tcph;

  		if (!pskb_may_pull(skb, ihl + sizeof(*tcph) + noff) ||

  		    skb_try_make_writable(skb, ihl + sizeof(*tcph) + noff))

  			goto drop;
  
  		tcph = (void *)(skb_network_header(skb) + ihl);

  		inet_proto_csum_replace4(&tcph->check, skb, addr, new_addr,
  					 true);

  		break;
  	}
  	case IPPROTO_UDP:
  	{
  		struct udphdr *udph;

  		if (!pskb_may_pull(skb, ihl + sizeof(*udph) + noff) ||

  		    skb_try_make_writable(skb, ihl + sizeof(*udph) + noff))

  			goto drop;
  
  		udph = (void *)(skb_network_header(skb) + ihl);
  		if (udph->check || skb->ip_summed == CHECKSUM_PARTIAL) {

  			inet_proto_csum_replace4(&udph->check, skb, addr,

  						 new_addr, true);

  			if (!udph->check)
  				udph->check = CSUM_MANGLED_0;
  		}
  		break;
  	}
  	case IPPROTO_ICMP:
  	{
  		struct icmphdr *icmph;

  		if (!pskb_may_pull(skb, ihl + sizeof(*icmph) + noff))

  			goto drop;
  
  		icmph = (void *)(skb_network_header(skb) + ihl);

  		if (!icmp_is_err(icmph->type))

  			break;

  		if (!pskb_may_pull(skb, ihl + sizeof(*icmph) + sizeof(*iph) +
  					noff))

  			goto drop;

  		icmph = (void *)(skb_network_header(skb) + ihl);

  		iph = (void *)(icmph + 1);
  		if (egress)
  			addr = iph->daddr;
  		else
  			addr = iph->saddr;
  
  		if ((old_addr ^ addr) & mask)
  			break;

  		if (skb_try_make_writable(skb, ihl + sizeof(*icmph) +
  					  sizeof(*iph) + noff))

  			goto drop;
  
  		icmph = (void *)(skb_network_header(skb) + ihl);
  		iph = (void *)(icmph + 1);
  
  		new_addr &= mask;
  		new_addr |= addr & ~mask;
  
  		/* XXX Fix up the inner checksums. */
  		if (egress)
  			iph->daddr = new_addr;
  		else
  			iph->saddr = new_addr;

  		inet_proto_csum_replace4(&icmph->checksum, skb, addr, new_addr,

  					 false);

  		break;
  	}
  	default:
  		break;
  	}

  out:

  	return action;
  
  drop:
  	spin_lock(&p->tcf_lock);
  	p->tcf_qstats.drops++;
  	spin_unlock(&p->tcf_lock);
  	return TC_ACT_SHOT;
  }
  
  static int tcf_nat_dump(struct sk_buff *skb, struct tc_action *a,
  			int bind, int ref)
  {
  	unsigned char *b = skb_tail_pointer(skb);

  	struct tcf_nat *p = to_tcf_nat(a);

  	struct tc_nat opt = {

  		.index    = p->tcf_index,

  		.refcnt   = refcount_read(&p->tcf_refcnt) - ref,
  		.bindcnt  = atomic_read(&p->tcf_bindcnt) - bind,

  	};

  	struct tcf_t t;

  	spin_lock_bh(&p->tcf_lock);
  	opt.old_addr = p->old_addr;
  	opt.new_addr = p->new_addr;
  	opt.mask = p->mask;
  	opt.flags = p->flags;
  	opt.action = p->tcf_action;

  	if (nla_put(skb, TCA_NAT_PARMS, sizeof(opt), &opt))
  		goto nla_put_failure;

  
  	tcf_tm_dump(&t, &p->tcf_tm);

  	if (nla_put_64bit(skb, TCA_NAT_TM, sizeof(t), &t, TCA_NAT_PAD))

  		goto nla_put_failure;

  	spin_unlock_bh(&p->tcf_lock);

  	return skb->len;

  nla_put_failure:

  	spin_unlock_bh(&p->tcf_lock);

  	nlmsg_trim(skb, b);

  	return -1;
  }

  static int tcf_nat_walker(struct net *net, struct sk_buff *skb,
  			  struct netlink_callback *cb, int type,

  			  const struct tc_action_ops *ops,
  			  struct netlink_ext_ack *extack)

  {
  	struct tc_action_net *tn = net_generic(net, nat_net_id);

  	return tcf_generic_walker(tn, skb, cb, type, ops, extack);

  }

  static int tcf_nat_search(struct net *net, struct tc_action **a, u32 index)

  {
  	struct tc_action_net *tn = net_generic(net, nat_net_id);

  	return tcf_idr_search(tn, a, index);

  }

  static struct tc_action_ops act_nat_ops = {
  	.kind		=	"nat",

  	.id		=	TCA_ID_NAT,

  	.owner		=	THIS_MODULE,

  	.act		=	tcf_nat_act,

  	.dump		=	tcf_nat_dump,

  	.init		=	tcf_nat_init,

  	.walk		=	tcf_nat_walker,
  	.lookup		=	tcf_nat_search,

  	.size		=	sizeof(struct tcf_nat),

  };
  
  static __net_init int nat_init_net(struct net *net)
  {
  	struct tc_action_net *tn = net_generic(net, nat_net_id);

  	return tc_action_net_init(net, tn, &act_nat_ops);

  }

  static void __net_exit nat_exit_net(struct list_head *net_list)

  {

  	tc_action_net_exit(net_list, nat_net_id);

  }
  
  static struct pernet_operations nat_net_ops = {
  	.init = nat_init_net,

  	.exit_batch = nat_exit_net,

  	.id   = &nat_net_id,
  	.size = sizeof(struct tc_action_net),

  };
  
  MODULE_DESCRIPTION("Stateless NAT actions");
  MODULE_LICENSE("GPL");
  
  static int __init nat_init_module(void)
  {

  	return tcf_register_action(&act_nat_ops, &nat_net_ops);

  }
  
  static void __exit nat_cleanup_module(void)
  {

  	tcf_unregister_action(&act_nat_ops, &nat_net_ops);

  }
  
  module_init(nat_init_module);
  module_exit(nat_cleanup_module);