/*
 *  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/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/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 DEFINE_PER_CPU(char [SEG6_HMAC_RING_SIZE], 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 = ARRAY_SIZE(hmac_algos);
        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) + 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();
        ring = this_cpu_ptr(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;
        }

        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_algo(void)
{
        struct seg6_hmac_algo *algo;
        struct crypto_shash *tfm;
        struct shash_desc *shash;
        int i, alg_count, cpu;

        alg_count = ARRAY_SIZE(hmac_algos);

        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 = raw_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_node(shsize, GFP_KERNEL,
                                             cpu_to_node(cpu));
                        if (!shash)
                                return -ENOMEM;
                        *per_cpu_ptr(algo->shashs, cpu) = shash;
                }
        }

        return 0;
}

int __init seg6_hmac_init(void)
{
        return seg6_hmac_init_algo();
}
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;

        alg_count = ARRAY_SIZE(hmac_algos);
        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);