net/ipv6/seg6_hmac.c

// SPDX-License-Identifier: GPL-2.0-or-later
/*
 *  SR-IPv6 implementation -- HMAC functions
 *
 *  Author:
 *  David Lebrun <david.lebrun@uclouvain.be>
 */

#include <linux/errno.h>
#include <linux/kernel.h>
#include <linux/types.h>
#include <linux/socket.h>
#include <linux/sockios.h>
#include <linux/net.h>
#include <linux/netdevice.h>
#include <linux/in6.h>
#include <linux/icmpv6.h>
#include <linux/mroute6.h>
#include <linux/rhashtable.h>

#include <linux/netfilter.h>
#include <linux/netfilter_ipv6.h>

#include <net/sock.h>
#include <net/snmp.h>

#include <net/ipv6.h>
#include <net/protocol.h>
#include <net/transp_v6.h>
#include <net/rawv6.h>
#include <net/ndisc.h>
#include <net/ip6_route.h>
#include <net/addrconf.h>
#include <net/xfrm.h>

#include <crypto/sha1.h>
#include <crypto/sha2.h>
#include <crypto/utils.h>
#include <net/seg6.h>
#include <net/genetlink.h>
#include <net/seg6_hmac.h>
#include <linux/random.h>

struct hmac_storage {
	local_lock_t bh_lock;
	char hmac_ring[SEG6_HMAC_RING_SIZE];
};

static DEFINE_PER_CPU(struct hmac_storage, hmac_storage) = {
	.bh_lock = INIT_LOCAL_LOCK(bh_lock),
};

static int seg6_hmac_cmpfn(struct rhashtable_compare_arg *arg, const void *obj)
{
	const struct seg6_hmac_info *hinfo = obj;

	return (hinfo->hmackeyid != *(__u32 *)arg->key);
}

static inline void seg6_hinfo_release(struct seg6_hmac_info *hinfo)
{
	kfree_rcu(hinfo, rcu);
}

static void seg6_free_hi(void *ptr, void *arg)
{
	struct seg6_hmac_info *hinfo = (struct seg6_hmac_info *)ptr;

	if (hinfo)
		seg6_hinfo_release(hinfo);
}

static const struct rhashtable_params rht_params = {
	.head_offset		= offsetof(struct seg6_hmac_info, node),
	.key_offset		= offsetof(struct seg6_hmac_info, hmackeyid),
	.key_len		= sizeof(u32),
	.automatic_shrinking	= true,
	.obj_cmpfn		= seg6_hmac_cmpfn,
};

static struct sr6_tlv_hmac *seg6_get_tlv_hmac(struct ipv6_sr_hdr *srh)
{
	struct sr6_tlv_hmac *tlv;

	if (srh->hdrlen < (srh->first_segment + 1) * 2 + 5)
		return NULL;

	if (!sr_has_hmac(srh))
		return NULL;

	tlv = (struct sr6_tlv_hmac *)
	      ((char *)srh + ((srh->hdrlen + 1) << 3) - 40);

	if (tlv->tlvhdr.type != SR6_TLV_HMAC || tlv->tlvhdr.len != 38)
		return NULL;

	return tlv;
}

int seg6_hmac_compute(struct seg6_hmac_info *hinfo, struct ipv6_sr_hdr *hdr,
		      struct in6_addr *saddr, u8 *output)
{
	__be32 hmackeyid = cpu_to_be32(hinfo->hmackeyid);
	int plen, i, ret = 0;
	char *ring, *off;

	/* saddr(16) + first_seg(1) + flags(1) + keyid(4) + seglist(16n) */
	plen = 16 + 1 + 1 + 4 + (hdr->first_segment + 1) * 16;

	/* this limit allows for 14 segments */
	if (plen >= SEG6_HMAC_RING_SIZE)
		return -EMSGSIZE;

	/* Let's build the HMAC text on the ring buffer. The text is composed
	 * as follows, in order:
	 *
	 * 1. Source IPv6 address (128 bits)
	 * 2. first_segment value (8 bits)
	 * 3. Flags (8 bits)
	 * 4. HMAC Key ID (32 bits)
	 * 5. All segments in the segments list (n * 128 bits)
	 */

	local_bh_disable();
	local_lock_nested_bh(&hmac_storage.bh_lock);
	ring = this_cpu_ptr(hmac_storage.hmac_ring);
	off = ring;

	/* source address */
	memcpy(off, saddr, 16);
	off += 16;

	/* first_segment value */
	*off++ = hdr->first_segment;

	/* flags */
	*off++ = hdr->flags;

	/* HMAC Key ID */
	memcpy(off, &hmackeyid, 4);
	off += 4;

	/* all segments in the list */
	for (i = 0; i < hdr->first_segment + 1; i++) {
		memcpy(off, hdr->segments + i, 16);
		off += 16;
	}

	switch (hinfo->alg_id) {
	case SEG6_HMAC_ALGO_SHA1:
		hmac_sha1(&hinfo->key.sha1, ring, plen, output);
		static_assert(SEG6_HMAC_FIELD_LEN > SHA1_DIGEST_SIZE);
		memset(&output[SHA1_DIGEST_SIZE], 0,
		       SEG6_HMAC_FIELD_LEN - SHA1_DIGEST_SIZE);
		break;
	case SEG6_HMAC_ALGO_SHA256:
		hmac_sha256(&hinfo->key.sha256, ring, plen, output);
		static_assert(SEG6_HMAC_FIELD_LEN == SHA256_DIGEST_SIZE);
		break;
	default:
		WARN_ON_ONCE(1);
		ret = -EINVAL;
		break;
	}
	local_unlock_nested_bh(&hmac_storage.bh_lock);
	local_bh_enable();
	return ret;
}
EXPORT_SYMBOL(seg6_hmac_compute);

/* checks if an incoming SR-enabled packet's HMAC status matches
 * the incoming policy.
 *
 * called with rcu_read_lock()
 */
bool seg6_hmac_validate_skb(struct sk_buff *skb)
{
	u8 hmac_output[SEG6_HMAC_FIELD_LEN];
	struct net *net = dev_net(skb->dev);
	struct seg6_hmac_info *hinfo;
	struct sr6_tlv_hmac *tlv;
	struct ipv6_sr_hdr *srh;
	struct inet6_dev *idev;
	int require_hmac;

	idev = __in6_dev_get(skb->dev);
	if (!idev)
		return false;

	srh = (struct ipv6_sr_hdr *)skb_transport_header(skb);

	tlv = seg6_get_tlv_hmac(srh);

	require_hmac = READ_ONCE(idev->cnf.seg6_require_hmac);
	/* mandatory check but no tlv */
	if (require_hmac > 0 && !tlv)
		return false;

	/* no check */
	if (require_hmac < 0)
		return true;

	/* check only if present */
	if (require_hmac == 0 && !tlv)
		return true;

	/* now, seg6_require_hmac >= 0 && tlv */

	hinfo = seg6_hmac_info_lookup(net, be32_to_cpu(tlv->hmackeyid));
	if (!hinfo)
		return false;

	if (seg6_hmac_compute(hinfo, srh, &ipv6_hdr(skb)->saddr, hmac_output))
		return false;

	if (crypto_memneq(hmac_output, tlv->hmac, SEG6_HMAC_FIELD_LEN))
		return false;

	return true;
}
EXPORT_SYMBOL(seg6_hmac_validate_skb);

/* called with rcu_read_lock() */
struct seg6_hmac_info *seg6_hmac_info_lookup(struct net *net, u32 key)
{
	struct seg6_pernet_data *sdata = seg6_pernet(net);
	struct seg6_hmac_info *hinfo;

	hinfo = rhashtable_lookup_fast(&sdata->hmac_infos, &key, rht_params);

	return hinfo;
}
EXPORT_SYMBOL(seg6_hmac_info_lookup);

int seg6_hmac_info_add(struct net *net, u32 key, struct seg6_hmac_info *hinfo)
{
	struct seg6_pernet_data *sdata = seg6_pernet(net);
	int err;

	switch (hinfo->alg_id) {
	case SEG6_HMAC_ALGO_SHA1:
		hmac_sha1_preparekey(&hinfo->key.sha1,
				     hinfo->secret, hinfo->slen);
		break;
	case SEG6_HMAC_ALGO_SHA256:
		hmac_sha256_preparekey(&hinfo->key.sha256,
				       hinfo->secret, hinfo->slen);
		break;
	default:
		return -EINVAL;
	}

	err = rhashtable_lookup_insert_fast(&sdata->hmac_infos, &hinfo->node,
					    rht_params);

	return err;
}
EXPORT_SYMBOL(seg6_hmac_info_add);

int seg6_hmac_info_del(struct net *net, u32 key)
{
	struct seg6_pernet_data *sdata = seg6_pernet(net);
	struct seg6_hmac_info *hinfo;
	int err = -ENOENT;

	hinfo = rhashtable_lookup_fast(&sdata->hmac_infos, &key, rht_params);
	if (!hinfo)
		goto out;

	err = rhashtable_remove_fast(&sdata->hmac_infos, &hinfo->node,
				     rht_params);
	if (err)
		goto out;

	seg6_hinfo_release(hinfo);

out:
	return err;
}
EXPORT_SYMBOL(seg6_hmac_info_del);

int seg6_push_hmac(struct net *net, struct in6_addr *saddr,
		   struct ipv6_sr_hdr *srh)
{
	struct seg6_hmac_info *hinfo;
	struct sr6_tlv_hmac *tlv;
	int err = -ENOENT;

	tlv = seg6_get_tlv_hmac(srh);
	if (!tlv)
		return -EINVAL;

	rcu_read_lock();

	hinfo = seg6_hmac_info_lookup(net, be32_to_cpu(tlv->hmackeyid));
	if (!hinfo)
		goto out;

	memset(tlv->hmac, 0, SEG6_HMAC_FIELD_LEN);
	err = seg6_hmac_compute(hinfo, srh, saddr, tlv->hmac);

out:
	rcu_read_unlock();
	return err;
}
EXPORT_SYMBOL(seg6_push_hmac);

int __net_init seg6_hmac_net_init(struct net *net)
{
	struct seg6_pernet_data *sdata = seg6_pernet(net);

	return rhashtable_init(&sdata->hmac_infos, &rht_params);
}

void __net_exit seg6_hmac_net_exit(struct net *net)
{
	struct seg6_pernet_data *sdata = seg6_pernet(net);

	rhashtable_free_and_destroy(&sdata->hmac_infos, seg6_free_hi, NULL);
}
EXPORT_SYMBOL(seg6_hmac_net_exit);