act_skbmod.c

/*
 * net/sched/act_skbmod.c  skb data modifier
 *
 * Copyright (c) 2016 Jamal Hadi Salim <jhs@mojatatu.com>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
*/

#include <linux/module.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/skbuff.h>
#include <linux/rtnetlink.h>
#include <net/netlink.h>
#include <net/pkt_sched.h>

#include <linux/tc_act/tc_skbmod.h>
#include <net/tc_act/tc_skbmod.h>

#define SKBMOD_TAB_MASK     15

static int skbmod_net_id;
static struct tc_action_ops act_skbmod_ops;

#define MAX_EDIT_LEN ETH_HLEN
static int tcf_skbmod_run(struct sk_buff *skb, const struct tc_action *a,
			  struct tcf_result *res)
{
	struct tcf_skbmod *d = to_skbmod(a);
	int action;
	struct tcf_skbmod_params *p;
	u64 flags;
	int err;

	tcf_lastuse_update(&d->tcf_tm);
	bstats_cpu_update(this_cpu_ptr(d->common.cpu_bstats), skb);

	/* XXX: if you are going to edit more fields beyond ethernet header
	 * (example when you add IP header replacement or vlan swap)
	 * then MAX_EDIT_LEN needs to change appropriately
	*/
	err = skb_ensure_writable(skb, MAX_EDIT_LEN);
	if (unlikely(err)) { /* best policy is to drop on the floor */
		qstats_overlimit_inc(this_cpu_ptr(d->common.cpu_qstats));
		return TC_ACT_SHOT;
	}

	rcu_read_lock();
	action = READ_ONCE(d->tcf_action);
	if (unlikely(action == TC_ACT_SHOT)) {
		qstats_overlimit_inc(this_cpu_ptr(d->common.cpu_qstats));
		rcu_read_unlock();
		return action;
	}

	p = rcu_dereference(d->skbmod_p);
	flags = p->flags;
	if (flags & SKBMOD_F_DMAC)
		ether_addr_copy(eth_hdr(skb)->h_dest, p->eth_dst);
	if (flags & SKBMOD_F_SMAC)
		ether_addr_copy(eth_hdr(skb)->h_source, p->eth_src);
	if (flags & SKBMOD_F_ETYPE)
		eth_hdr(skb)->h_proto = p->eth_type;
	rcu_read_unlock();

	if (flags & SKBMOD_F_SWAPMAC) {
		u16 tmpaddr[ETH_ALEN / 2]; /* ether_addr_copy() requirement */
		/*XXX: I am sure we can come up with more efficient swapping*/
		ether_addr_copy((u8 *)tmpaddr, eth_hdr(skb)->h_dest);
		ether_addr_copy(eth_hdr(skb)->h_dest, eth_hdr(skb)->h_source);
		ether_addr_copy(eth_hdr(skb)->h_source, (u8 *)tmpaddr);
	}

	return action;
}

static const struct nla_policy skbmod_policy[TCA_SKBMOD_MAX + 1] = {
	[TCA_SKBMOD_PARMS]		= { .len = sizeof(struct tc_skbmod) },
	[TCA_SKBMOD_DMAC]		= { .len = ETH_ALEN },
	[TCA_SKBMOD_SMAC]		= { .len = ETH_ALEN },
	[TCA_SKBMOD_ETYPE]		= { .type = NLA_U16 },
};

static int tcf_skbmod_init(struct net *net, struct nlattr *nla,
			   struct nlattr *est, struct tc_action **a,
			   int ovr, int bind)
{
	struct tc_action_net *tn = net_generic(net, skbmod_net_id);
	struct nlattr *tb[TCA_SKBMOD_MAX + 1];
	struct tcf_skbmod_params *p, *p_old;
	struct tc_skbmod *parm;
	struct tcf_skbmod *d;
	bool exists = false;
	u8 *daddr = NULL;
	u8 *saddr = NULL;
	u16 eth_type = 0;
	u32 lflags = 0;
	int ret = 0, err;

	if (!nla)
		return -EINVAL;

	err = nla_parse_nested(tb, TCA_SKBMOD_MAX, nla, skbmod_policy);
	if (err < 0)
		return err;

	if (!tb[TCA_SKBMOD_PARMS])
		return -EINVAL;

	if (tb[TCA_SKBMOD_DMAC]) {
		daddr = nla_data(tb[TCA_SKBMOD_DMAC]);
		lflags |= SKBMOD_F_DMAC;
	}

	if (tb[TCA_SKBMOD_SMAC]) {
		saddr = nla_data(tb[TCA_SKBMOD_SMAC]);
		lflags |= SKBMOD_F_SMAC;
	}

	if (tb[TCA_SKBMOD_ETYPE]) {
		eth_type = nla_get_u16(tb[TCA_SKBMOD_ETYPE]);
		lflags |= SKBMOD_F_ETYPE;
	}

	parm = nla_data(tb[TCA_SKBMOD_PARMS]);
	if (parm->flags & SKBMOD_F_SWAPMAC)
		lflags = SKBMOD_F_SWAPMAC;

	exists = tcf_hash_check(tn, parm->index, a, bind);
	if (exists && bind)
		return 0;

	if (!lflags)
		return -EINVAL;

	if (!exists) {
		ret = tcf_hash_create(tn, parm->index, est, a,
				      &act_skbmod_ops, bind, true);
		if (ret)
			return ret;

		ret = ACT_P_CREATED;
	} else {
		tcf_hash_release(*a, bind);
		if (!ovr)
			return -EEXIST;
	}

	d = to_skbmod(*a);

	ASSERT_RTNL();
	p = kzalloc(sizeof(struct tcf_skbmod_params), GFP_KERNEL);
	if (unlikely(!p)) {
		if (ovr)
			tcf_hash_release(*a, bind);
		return -ENOMEM;
	}

	p->flags = lflags;
	d->tcf_action = parm->action;

	p_old = rtnl_dereference(d->skbmod_p);

	if (ovr)
		spin_lock_bh(&d->tcf_lock);

	if (lflags & SKBMOD_F_DMAC)
		ether_addr_copy(p->eth_dst, daddr);
	if (lflags & SKBMOD_F_SMAC)
		ether_addr_copy(p->eth_src, saddr);
	if (lflags & SKBMOD_F_ETYPE)
		p->eth_type = htons(eth_type);

	rcu_assign_pointer(d->skbmod_p, p);
	if (ovr)
		spin_unlock_bh(&d->tcf_lock);

	if (p_old)
		kfree_rcu(p_old, rcu);

	if (ret == ACT_P_CREATED)
		tcf_hash_insert(tn, *a);
	return ret;
}

static void tcf_skbmod_cleanup(struct tc_action *a, int bind)
{
	struct tcf_skbmod *d = to_skbmod(a);
	struct tcf_skbmod_params  *p;

	p = rcu_dereference_protected(d->skbmod_p, 1);
	kfree_rcu(p, rcu);
}

static int tcf_skbmod_dump(struct sk_buff *skb, struct tc_action *a,
			   int bind, int ref)
{
	struct tcf_skbmod *d = to_skbmod(a);
	unsigned char *b = skb_tail_pointer(skb);
	struct tcf_skbmod_params  *p = rtnl_dereference(d->skbmod_p);
	struct tc_skbmod opt = {
		.index   = d->tcf_index,
		.refcnt  = d->tcf_refcnt - ref,
		.bindcnt = d->tcf_bindcnt - bind,
		.action  = d->tcf_action,
	};
	struct tcf_t t;

	opt.flags  = p->flags;
	if (nla_put(skb, TCA_SKBMOD_PARMS, sizeof(opt), &opt))
		goto nla_put_failure;
	if ((p->flags & SKBMOD_F_DMAC) &&
	    nla_put(skb, TCA_SKBMOD_DMAC, ETH_ALEN, p->eth_dst))
		goto nla_put_failure;
	if ((p->flags & SKBMOD_F_SMAC) &&
	    nla_put(skb, TCA_SKBMOD_SMAC, ETH_ALEN, p->eth_src))
		goto nla_put_failure;
	if ((p->flags & SKBMOD_F_ETYPE) &&
	    nla_put_u16(skb, TCA_SKBMOD_ETYPE, ntohs(p->eth_type)))
		goto nla_put_failure;

	tcf_tm_dump(&t, &d->tcf_tm);
	if (nla_put_64bit(skb, TCA_SKBMOD_TM, sizeof(t), &t, TCA_SKBMOD_PAD))
		goto nla_put_failure;

	return skb->len;
nla_put_failure:
	rcu_read_unlock();
	nlmsg_trim(skb, b);
	return -1;
}

static int tcf_skbmod_walker(struct net *net, struct sk_buff *skb,
			     struct netlink_callback *cb, int type,
			     const struct tc_action_ops *ops)
{
	struct tc_action_net *tn = net_generic(net, skbmod_net_id);

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

static int tcf_skbmod_search(struct net *net, struct tc_action **a, u32 index)
{
	struct tc_action_net *tn = net_generic(net, skbmod_net_id);

	return tcf_hash_search(tn, a, index);
}

static struct tc_action_ops act_skbmod_ops = {
	.kind		=	"skbmod",
	.type		=	TCA_ACT_SKBMOD,
	.owner		=	THIS_MODULE,
	.act		=	tcf_skbmod_run,
	.dump		=	tcf_skbmod_dump,
	.init		=	tcf_skbmod_init,
	.cleanup	=	tcf_skbmod_cleanup,
	.walk		=	tcf_skbmod_walker,
	.lookup		=	tcf_skbmod_search,
	.size		=	sizeof(struct tcf_skbmod),
};

static __net_init int skbmod_init_net(struct net *net)
{
	struct tc_action_net *tn = net_generic(net, skbmod_net_id);

	return tc_action_net_init(tn, &act_skbmod_ops, SKBMOD_TAB_MASK);
}

static void __net_exit skbmod_exit_net(struct net *net)
{
	struct tc_action_net *tn = net_generic(net, skbmod_net_id);

	tc_action_net_exit(tn);
}

static struct pernet_operations skbmod_net_ops = {
	.init = skbmod_init_net,
	.exit = skbmod_exit_net,
	.id   = &skbmod_net_id,
	.size = sizeof(struct tc_action_net),
};

MODULE_AUTHOR("Jamal Hadi Salim, <jhs@mojatatu.com>");
MODULE_DESCRIPTION("SKB data mod-ing");
MODULE_LICENSE("GPL");

static int __init skbmod_init_module(void)
{
	return tcf_register_action(&act_skbmod_ops, &skbmod_net_ops);
}

static void __exit skbmod_cleanup_module(void)
{
	tcf_unregister_action(&act_skbmod_ops, &skbmod_net_ops);
}

module_init(skbmod_init_module);
module_exit(skbmod_cleanup_module);