ipv6: sr: add core files for SR HMAC support

This patch adds the necessary functions to compute and check the HMAC signature
of an SR-enabled packet. Two HMAC algorithms are supported: hmac(sha1) and
hmac(sha256).

In order to avoid dynamic memory allocation for each HMAC computation,
a per-cpu ring buffer is allocated for this purpose.

A new per-interface sysctl called seg6_require_hmac is added, allowing a
user-defined policy for processing HMAC-signed SR-enabled packets.
A value of -1 means that the HMAC field will always be ignored.
A value of 0 means that if an HMAC field is present, its validity will
be enforced (the packet is dropped is the signature is incorrect).
Finally, a value of 1 means that any SR-enabled packet that does not
contain an HMAC signature or whose signature is incorrect will be dropped.

Signed-off-by: David Lebrun <david.lebrun@uclouvain.be>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 484 insertions, 0 deletions

diff --git a/net/ipv6/seg6_hmac.c b/net/ipv6/seg6_hmac.c
new file mode 100644
index 000000000000..ef1c8a46e7ac
--- /dev/null
+++ b/net/ipv6/seg6_hmac.c
@@ -0,0 +1,484 @@
+/*
+ *  SR-IPv6 implementation -- HMAC functions
+ *
+ *  Author:
+ *  David Lebrun <david.lebrun@uclouvain.be>
+ *
+ *
+ *  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/errno.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/slab.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 <linux/cryptohash.h>
+#include <crypto/hash.h>
+#include <crypto/sha.h>
+#include <net/seg6.h>
+#include <net/genetlink.h>
+#include <net/seg6_hmac.h>
+#include <linux/random.h>
+
+static char * __percpu *hmac_ring;
+
+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 seg6_hmac_algo hmac_algos[] = {
+	{
+		.alg_id = SEG6_HMAC_ALGO_SHA1,
+		.name = "hmac(sha1)",
+	},
+	{
+		.alg_id = SEG6_HMAC_ALGO_SHA256,
+		.name = "hmac(sha256)",
+	},
+};
+
+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;
+}
+
+static struct seg6_hmac_algo *__hmac_get_algo(u8 alg_id)
+{
+	struct seg6_hmac_algo *algo;
+	int i, alg_count;
+
+	alg_count = sizeof(hmac_algos) / sizeof(struct seg6_hmac_algo);
+	for (i = 0; i < alg_count; i++) {
+		algo = &hmac_algos[i];
+		if (algo->alg_id == alg_id)
+			return algo;
+	}
+
+	return NULL;
+}
+
+static int __do_hmac(struct seg6_hmac_info *hinfo, const char *text, u8 psize,
+		     u8 *output, int outlen)
+{
+	struct seg6_hmac_algo *algo;
+	struct crypto_shash *tfm;
+	struct shash_desc *shash;
+	int ret, dgsize;
+
+	algo = __hmac_get_algo(hinfo->alg_id);
+	if (!algo)
+		return -ENOENT;
+
+	tfm = *this_cpu_ptr(algo->tfms);
+
+	dgsize = crypto_shash_digestsize(tfm);
+	if (dgsize > outlen) {
+		pr_debug("sr-ipv6: __do_hmac: digest size too big (%d / %d)\n",
+			 dgsize, outlen);
+		return -ENOMEM;
+	}
+
+	ret = crypto_shash_setkey(tfm, hinfo->secret, hinfo->slen);
+	if (ret < 0) {
+		pr_debug("sr-ipv6: crypto_shash_setkey failed: err %d\n", ret);
+		goto failed;
+	}
+
+	shash = *this_cpu_ptr(algo->shashs);
+	shash->tfm = tfm;
+
+	ret = crypto_shash_digest(shash, text, psize, output);
+	if (ret < 0) {
+		pr_debug("sr-ipv6: crypto_shash_digest failed: err %d\n", ret);
+		goto failed;
+	}
+
+	return dgsize;
+
+failed:
+	return ret;
+}
+
+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);
+	u8 tmp_out[SEG6_HMAC_MAX_DIGESTSIZE];
+	int plen, i, dgsize, wrsize;
+	char *ring, *off;
+
+	/* a 160-byte buffer for digest output allows to store highest known
+	 * hash function (RadioGatun) with up to 1216 bits
+	 */
+
+	/* saddr(16) + first_seg(1) + cleanup(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. cleanup flag (8 bits: highest bit is cleanup value, others are 0)
+	 * 4. HMAC Key ID (32 bits)
+	 * 5. All segments in the segments list (n * 128 bits)
+	 */
+
+	local_bh_disable();
+	ring = *this_cpu_ptr(hmac_ring);
+	off = ring;
+
+	/* source address */
+	memcpy(off, saddr, 16);
+	off += 16;
+
+	/* first_segment value */
+	*off++ = hdr->first_segment;
+
+	/* cleanup flag */
+	*off++ = !!(sr_has_cleanup(hdr)) << 7;
+
+	/* 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;
+	}
+
+	dgsize = __do_hmac(hinfo, ring, plen, tmp_out,
+			   SEG6_HMAC_MAX_DIGESTSIZE);
+	local_bh_enable();
+
+	if (dgsize < 0)
+		return dgsize;
+
+	wrsize = SEG6_HMAC_FIELD_LEN;
+	if (wrsize > dgsize)
+		wrsize = dgsize;
+
+	memset(output, 0, SEG6_HMAC_FIELD_LEN);
+	memcpy(output, tmp_out, wrsize);
+
+	return 0;
+}
+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;
+
+	idev = __in6_dev_get(skb->dev);
+
+	srh = (struct ipv6_sr_hdr *)skb_transport_header(skb);
+
+	tlv = seg6_get_tlv_hmac(srh);
+
+	/* mandatory check but no tlv */
+	if (idev->cnf.seg6_require_hmac > 0 && !tlv)
+		return false;
+
+	/* no check */
+	if (idev->cnf.seg6_require_hmac < 0)
+		return true;
+
+	/* check only if present */
+	if (idev->cnf.seg6_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 (memcmp(hmac_output, tlv->hmac, SEG6_HMAC_FIELD_LEN) != 0)
+		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;
+
+	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);
+
+static int seg6_hmac_init_ring(void)
+{
+	int i;
+
+	hmac_ring = alloc_percpu(char *);
+
+	if (!hmac_ring)
+		return -ENOMEM;
+
+	for_each_possible_cpu(i) {
+		char *ring = kzalloc(SEG6_HMAC_RING_SIZE, GFP_KERNEL);
+
+		if (!ring)
+			return -ENOMEM;
+
+		*per_cpu_ptr(hmac_ring, i) = ring;
+	}
+
+	return 0;
+}
+
+static int seg6_hmac_init_algo(void)
+{
+	struct seg6_hmac_algo *algo;
+	struct crypto_shash *tfm;
+	struct shash_desc *shash;
+	int i, alg_count, cpu;
+
+	alg_count = sizeof(hmac_algos) / sizeof(struct seg6_hmac_algo);
+
+	for (i = 0; i < alg_count; i++) {
+		struct crypto_shash **p_tfm;
+		int shsize;
+
+		algo = &hmac_algos[i];
+		algo->tfms = alloc_percpu(struct crypto_shash *);
+		if (!algo->tfms)
+			return -ENOMEM;
+
+		for_each_possible_cpu(cpu) {
+			tfm = crypto_alloc_shash(algo->name, 0, GFP_KERNEL);
+			if (IS_ERR(tfm))
+				return PTR_ERR(tfm);
+			p_tfm = per_cpu_ptr(algo->tfms, cpu);
+			*p_tfm = tfm;
+		}
+
+		p_tfm = this_cpu_ptr(algo->tfms);
+		tfm = *p_tfm;
+
+		shsize = sizeof(*shash) + crypto_shash_descsize(tfm);
+
+		algo->shashs = alloc_percpu(struct shash_desc *);
+		if (!algo->shashs)
+			return -ENOMEM;
+
+		for_each_possible_cpu(cpu) {
+			shash = kzalloc(shsize, GFP_KERNEL);
+			if (!shash)
+				return -ENOMEM;
+			*per_cpu_ptr(algo->shashs, cpu) = shash;
+		}
+	}
+
+	return 0;
+}
+
+int __init seg6_hmac_init(void)
+{
+	int ret;
+
+	ret = seg6_hmac_init_ring();
+	if (ret < 0)
+		goto out;
+
+	ret = seg6_hmac_init_algo();
+
+out:
+	return ret;
+}
+EXPORT_SYMBOL(seg6_hmac_init);
+
+int __net_init seg6_hmac_net_init(struct net *net)
+{
+	struct seg6_pernet_data *sdata = seg6_pernet(net);
+
+	rhashtable_init(&sdata->hmac_infos, &rht_params);
+
+	return 0;
+}
+EXPORT_SYMBOL(seg6_hmac_net_init);
+
+void seg6_hmac_exit(void)
+{
+	struct seg6_hmac_algo *algo = NULL;
+	int i, alg_count, cpu;
+
+	for_each_possible_cpu(i) {
+		char *ring = *per_cpu_ptr(hmac_ring, i);
+
+		kfree(ring);
+	}
+	free_percpu(hmac_ring);
+
+	alg_count = sizeof(hmac_algos) / sizeof(struct seg6_hmac_algo);
+	for (i = 0; i < alg_count; i++) {
+		algo = &hmac_algos[i];
+		for_each_possible_cpu(cpu) {
+			struct crypto_shash *tfm;
+			struct shash_desc *shash;
+
+			shash = *per_cpu_ptr(algo->shashs, cpu);
+			kfree(shash);
+			tfm = *per_cpu_ptr(algo->tfms, cpu);
+			crypto_free_shash(tfm);
+		}
+		free_percpu(algo->tfms);
+		free_percpu(algo->shashs);
+	}
+}
+EXPORT_SYMBOL(seg6_hmac_exit);
+
+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);