linux-stable/net/netfilter/nf_bpf_link.c

// SPDX-License-Identifier: GPL-2.0
#include <linux/bpf.h>
#include <linux/netfilter.h>

#include <net/netfilter/nf_bpf_link.h>
#include <uapi/linux/netfilter_ipv4.h>

static unsigned int nf_hook_run_bpf(void *bpf_prog, struct sk_buff *skb,
				    const struct nf_hook_state *s)
{
	return NF_ACCEPT;
}

struct bpf_nf_link {
	struct bpf_link link;
	struct nf_hook_ops hook_ops;
	struct net *net;
	u32 dead;
};

static void bpf_nf_link_release(struct bpf_link *link)
{
	struct bpf_nf_link *nf_link = container_of(link, struct bpf_nf_link, link);

	if (nf_link->dead)
		return;

	/* prevent hook-not-found warning splat from netfilter core when
	 * .detach was already called
	 */
	if (!cmpxchg(&nf_link->dead, 0, 1))
		nf_unregister_net_hook(nf_link->net, &nf_link->hook_ops);
}

static void bpf_nf_link_dealloc(struct bpf_link *link)
{
	struct bpf_nf_link *nf_link = container_of(link, struct bpf_nf_link, link);

	kfree(nf_link);
}

static int bpf_nf_link_detach(struct bpf_link *link)
{
	bpf_nf_link_release(link);
	return 0;
}

static void bpf_nf_link_show_info(const struct bpf_link *link,
				  struct seq_file *seq)
{
	struct bpf_nf_link *nf_link = container_of(link, struct bpf_nf_link, link);

	seq_printf(seq, "pf:\t%u\thooknum:\t%u\tprio:\t%d\n",
		   nf_link->hook_ops.pf, nf_link->hook_ops.hooknum,
		   nf_link->hook_ops.priority);
}

static int bpf_nf_link_fill_link_info(const struct bpf_link *link,
				      struct bpf_link_info *info)
{
	struct bpf_nf_link *nf_link = container_of(link, struct bpf_nf_link, link);

	info->netfilter.pf = nf_link->hook_ops.pf;
	info->netfilter.hooknum = nf_link->hook_ops.hooknum;
	info->netfilter.priority = nf_link->hook_ops.priority;
	info->netfilter.flags = 0;

	return 0;
}

static int bpf_nf_link_update(struct bpf_link *link, struct bpf_prog *new_prog,
			      struct bpf_prog *old_prog)
{
	return -EOPNOTSUPP;
}

static const struct bpf_link_ops bpf_nf_link_lops = {
	.release = bpf_nf_link_release,
	.dealloc = bpf_nf_link_dealloc,
	.detach = bpf_nf_link_detach,
	.show_fdinfo = bpf_nf_link_show_info,
	.fill_link_info = bpf_nf_link_fill_link_info,
	.update_prog = bpf_nf_link_update,
};

static int bpf_nf_check_pf_and_hooks(const union bpf_attr *attr)
{
	switch (attr->link_create.netfilter.pf) {
	case NFPROTO_IPV4:
	case NFPROTO_IPV6:
		if (attr->link_create.netfilter.hooknum >= NF_INET_NUMHOOKS)
			return -EPROTO;
		break;
	default:
		return -EAFNOSUPPORT;
	}

	if (attr->link_create.netfilter.flags)
		return -EOPNOTSUPP;

	/* make sure conntrack confirm is always last.
	 *
	 * In the future, if userspace can e.g. request defrag, then
	 * "defrag_requested && prio before NF_IP_PRI_CONNTRACK_DEFRAG"
	 * should fail.
	 */
	switch (attr->link_create.netfilter.priority) {
	case NF_IP_PRI_FIRST: return -ERANGE; /* sabotage_in and other warts */
	case NF_IP_PRI_LAST: return -ERANGE; /* e.g. conntrack confirm */
	}

	return 0;
}

int bpf_nf_link_attach(const union bpf_attr *attr, struct bpf_prog *prog)
{
	struct net *net = current->nsproxy->net_ns;
	struct bpf_link_primer link_primer;
	struct bpf_nf_link *link;
	int err;

	if (attr->link_create.flags)
		return -EINVAL;

	err = bpf_nf_check_pf_and_hooks(attr);
	if (err)
		return err;

	link = kzalloc(sizeof(*link), GFP_USER);
	if (!link)
		return -ENOMEM;

	bpf_link_init(&link->link, BPF_LINK_TYPE_NETFILTER, &bpf_nf_link_lops, prog);

	link->hook_ops.hook = nf_hook_run_bpf;
	link->hook_ops.hook_ops_type = NF_HOOK_OP_BPF;
	link->hook_ops.priv = prog;

	link->hook_ops.pf = attr->link_create.netfilter.pf;
	link->hook_ops.priority = attr->link_create.netfilter.priority;
	link->hook_ops.hooknum = attr->link_create.netfilter.hooknum;

	link->net = net;
	link->dead = false;

	err = bpf_link_prime(&link->link, &link_primer);
	if (err) {
		kfree(link);
		return err;
	}

	err = nf_register_net_hook(net, &link->hook_ops);
	if (err) {
		bpf_link_cleanup(&link_primer);
		return err;
	}

	return bpf_link_settle(&link_primer);
}