#define pr_fmt(fmt) "IPsec: " fmt

#include <crypto/algapi.h>
#include <crypto/hash.h>
#include <linux/err.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <net/ip.h>
#include <net/xfrm.h>
#include <net/ah.h>
#include <linux/crypto.h>
#include <linux/pfkeyv2.h>
#include <linux/scatterlist.h>
#include <net/icmp.h>
#include <net/protocol.h>

struct ah_skb_cb {
        struct xfrm_skb_cb xfrm;
        void *tmp;
};

#define AH_SKB_CB(__skb) ((struct ah_skb_cb *)&((__skb)->cb[0]))

static void *ah_alloc_tmp(struct crypto_ahash *ahash, int nfrags,
                          unsigned int size)
{
        unsigned int len;

        len = size + crypto_ahash_digestsize(ahash) +
              (crypto_ahash_alignmask(ahash) &
               ~(crypto_tfm_ctx_alignment() - 1));

        len = ALIGN(len, crypto_tfm_ctx_alignment());

        len += sizeof(struct ahash_request) + crypto_ahash_reqsize(ahash);
        len = ALIGN(len, __alignof__(struct scatterlist));

        len += sizeof(struct scatterlist) * nfrags;

        return kmalloc(len, GFP_ATOMIC);
}

static inline u8 *ah_tmp_auth(void *tmp, unsigned int offset)
{
        return tmp + offset;
}

static inline u8 *ah_tmp_icv(struct crypto_ahash *ahash, void *tmp,
                             unsigned int offset)
{
        return PTR_ALIGN((u8 *)tmp + offset, crypto_ahash_alignmask(ahash) + 1);
}

static inline struct ahash_request *ah_tmp_req(struct crypto_ahash *ahash,
                                               u8 *icv)
{
        struct ahash_request *req;

        req = (void *)PTR_ALIGN(icv + crypto_ahash_digestsize(ahash),
                                crypto_tfm_ctx_alignment());

        ahash_request_set_tfm(req, ahash);

        return req;
}

static inline struct scatterlist *ah_req_sg(struct crypto_ahash *ahash,
                                             struct ahash_request *req)
{
        return (void *)ALIGN((unsigned long)(req + 1) +
                             crypto_ahash_reqsize(ahash),
                             __alignof__(struct scatterlist));
}

/* Clear mutable options and find final destination to substitute
 * into IP header for icv calculation. Options are already checked
 * for validity, so paranoia is not required. */

static int ip_clear_mutable_options(const struct iphdr *iph, __be32 *daddr)
{
        unsigned char *optptr = (unsigned char *)(iph+1);
        int  l = iph->ihl*4 - sizeof(struct iphdr);
        int  optlen;

        while (l > 0) {
                switch (*optptr) {
                case IPOPT_END:
                        return 0;
                case IPOPT_NOOP:
                        l--;
                        optptr++;
                        continue;
                }
                optlen = optptr[1];
                if (optlen<2 || optlen>l)
                        return -EINVAL;
                switch (*optptr) {
                case IPOPT_SEC:
                case 0x85:      /* Some "Extended Security" crap. */
                case IPOPT_CIPSO:
                case IPOPT_RA:
                case 0x80|21:   /* RFC1770 */
                        break;
                case IPOPT_LSRR:
                case IPOPT_SSRR:
                        if (optlen < 6)
                                return -EINVAL;
                        memcpy(daddr, optptr+optlen-4, 4);
                        /* Fall through */
                default:
                        memset(optptr, 0, optlen);
                }
                l -= optlen;
                optptr += optlen;
        }
        return 0;
}

static void ah_output_done(struct crypto_async_request *base, int err)
{
        u8 *icv;
        struct iphdr *iph;
        struct sk_buff *skb = base->data;
        struct xfrm_state *x = skb_dst(skb)->xfrm;
        struct ah_data *ahp = x->data;
        struct iphdr *top_iph = ip_hdr(skb);
        struct ip_auth_hdr *ah = ip_auth_hdr(skb);
        int ihl = ip_hdrlen(skb);

        iph = AH_SKB_CB(skb)->tmp;
        icv = ah_tmp_icv(ahp->ahash, iph, ihl);
        memcpy(ah->auth_data, icv, ahp->icv_trunc_len);

        top_iph->tos = iph->tos;
        top_iph->ttl = iph->ttl;
        top_iph->frag_off = iph->frag_off;
        if (top_iph->ihl != 5) {
                top_iph->daddr = iph->daddr;
                memcpy(top_iph+1, iph+1, top_iph->ihl*4 - sizeof(struct iphdr));
        }

        kfree(AH_SKB_CB(skb)->tmp);
        xfrm_output_resume(skb, err);
}

static int ah_output(struct xfrm_state *x, struct sk_buff *skb)
{
        int err;
        int nfrags;
        int ihl;
        u8 *icv;
        struct sk_buff *trailer;
        struct crypto_ahash *ahash;
        struct ahash_request *req;
        struct scatterlist *sg;
        struct iphdr *iph, *top_iph;
        struct ip_auth_hdr *ah;
        struct ah_data *ahp;
        int seqhi_len = 0;
        __be32 *seqhi;
        int sglists = 0;
        struct scatterlist *seqhisg;

        ahp = x->data;
        ahash = ahp->ahash;

        if ((err = skb_cow_data(skb, 0, &trailer)) < 0)
                goto out;
        nfrags = err;

        skb_push(skb, -skb_network_offset(skb));
        ah = ip_auth_hdr(skb);
        ihl = ip_hdrlen(skb);

        if (x->props.flags & XFRM_STATE_ESN) {
                sglists = 1;
                seqhi_len = sizeof(*seqhi);
        }
        err = -ENOMEM;
        iph = ah_alloc_tmp(ahash, nfrags + sglists, ihl + seqhi_len);
        if (!iph)
                goto out;
        seqhi = (__be32 *)((char *)iph + ihl);
        icv = ah_tmp_icv(ahash, seqhi, seqhi_len);
        req = ah_tmp_req(ahash, icv);
        sg = ah_req_sg(ahash, req);
        seqhisg = sg + nfrags;

        memset(ah->auth_data, 0, ahp->icv_trunc_len);

        top_iph = ip_hdr(skb);

        iph->tos = top_iph->tos;
        iph->ttl = top_iph->ttl;
        iph->frag_off = top_iph->frag_off;

        if (top_iph->ihl != 5) {
                iph->daddr = top_iph->daddr;
                memcpy(iph+1, top_iph+1, top_iph->ihl*4 - sizeof(struct iphdr));
                err = ip_clear_mutable_options(top_iph, &top_iph->daddr);
                if (err)
                        goto out_free;
        }

        ah->nexthdr = *skb_mac_header(skb);
        *skb_mac_header(skb) = IPPROTO_AH;

        top_iph->tos = 0;
        top_iph->tot_len = htons(skb->len);
        top_iph->frag_off = 0;
        top_iph->ttl = 0;
        top_iph->check = 0;

        if (x->props.flags & XFRM_STATE_ALIGN4)
                ah->hdrlen  = (XFRM_ALIGN4(sizeof(*ah) + ahp->icv_trunc_len) >> 2) - 2;
        else
                ah->hdrlen  = (XFRM_ALIGN8(sizeof(*ah) + ahp->icv_trunc_len) >> 2) - 2;

        ah->reserved = 0;
        ah->spi = x->id.spi;
        ah->seq_no = htonl(XFRM_SKB_CB(skb)->seq.output.low);

        sg_init_table(sg, nfrags + sglists);
        err = skb_to_sgvec_nomark(skb, sg, 0, skb->len);
        if (unlikely(err < 0))
                goto out_free;

        if (x->props.flags & XFRM_STATE_ESN) {
                /* Attach seqhi sg right after packet payload */
                *seqhi = htonl(XFRM_SKB_CB(skb)->seq.output.hi);
                sg_set_buf(seqhisg, seqhi, seqhi_len);
        }
        ahash_request_set_crypt(req, sg, icv, skb->len + seqhi_len);
        ahash_request_set_callback(req, 0, ah_output_done, skb);

        AH_SKB_CB(skb)->tmp = iph;

        err = crypto_ahash_digest(req);
        if (err) {
                if (err == -EINPROGRESS)
                        goto out;

                if (err == -ENOSPC)
                        err = NET_XMIT_DROP;
                goto out_free;
        }

        memcpy(ah->auth_data, icv, ahp->icv_trunc_len);

        top_iph->tos = iph->tos;
        top_iph->ttl = iph->ttl;
        top_iph->frag_off = iph->frag_off;
        if (top_iph->ihl != 5) {
                top_iph->daddr = iph->daddr;
                memcpy(top_iph+1, iph+1, top_iph->ihl*4 - sizeof(struct iphdr));
        }

out_free:
        kfree(iph);
out:
        return err;
}

static void ah_input_done(struct crypto_async_request *base, int err)
{
        u8 *auth_data;
        u8 *icv;
        struct iphdr *work_iph;
        struct sk_buff *skb = base->data;
        struct xfrm_state *x = xfrm_input_state(skb);
        struct ah_data *ahp = x->data;
        struct ip_auth_hdr *ah = ip_auth_hdr(skb);
        int ihl = ip_hdrlen(skb);
        int ah_hlen = (ah->hdrlen + 2) << 2;

        if (err)
                goto out;

        work_iph = AH_SKB_CB(skb)->tmp;
        auth_data = ah_tmp_auth(work_iph, ihl);
        icv = ah_tmp_icv(ahp->ahash, auth_data, ahp->icv_trunc_len);

        err = crypto_memneq(icv, auth_data, ahp->icv_trunc_len) ? -EBADMSG : 0;
        if (err)
                goto out;

        err = ah->nexthdr;

        skb->network_header += ah_hlen;
        memcpy(skb_network_header(skb), work_iph, ihl);
        __skb_pull(skb, ah_hlen + ihl);

        if (x->props.mode == XFRM_MODE_TUNNEL)
                skb_reset_transport_header(skb);
        else
                skb_set_transport_header(skb, -ihl);
out:
        kfree(AH_SKB_CB(skb)->tmp);
        xfrm_input_resume(skb, err);
}

static int ah_input(struct xfrm_state *x, struct sk_buff *skb)
{
        int ah_hlen;
        int ihl;
        int nexthdr;
        int nfrags;
        u8 *auth_data;
        u8 *icv;
        struct sk_buff *trailer;
        struct crypto_ahash *ahash;
        struct ahash_request *req;
        struct scatterlist *sg;
        struct iphdr *iph, *work_iph;
        struct ip_auth_hdr *ah;
        struct ah_data *ahp;
        int err = -ENOMEM;
        int seqhi_len = 0;
        __be32 *seqhi;
        int sglists = 0;
        struct scatterlist *seqhisg;

        if (!pskb_may_pull(skb, sizeof(*ah)))
                goto out;

        ah = (struct ip_auth_hdr *)skb->data;
        ahp = x->data;
        ahash = ahp->ahash;

        nexthdr = ah->nexthdr;
        ah_hlen = (ah->hdrlen + 2) << 2;

        if (x->props.flags & XFRM_STATE_ALIGN4) {
                if (ah_hlen != XFRM_ALIGN4(sizeof(*ah) + ahp->icv_full_len) &&
                    ah_hlen != XFRM_ALIGN4(sizeof(*ah) + ahp->icv_trunc_len))
                        goto out;
        } else {
                if (ah_hlen != XFRM_ALIGN8(sizeof(*ah) + ahp->icv_full_len) &&
                    ah_hlen != XFRM_ALIGN8(sizeof(*ah) + ahp->icv_trunc_len))
                        goto out;
        }

        if (!pskb_may_pull(skb, ah_hlen))
                goto out;

        /* We are going to _remove_ AH header to keep sockets happy,
         * so... Later this can change. */
        if (skb_unclone(skb, GFP_ATOMIC))
                goto out;

        skb->ip_summed = CHECKSUM_NONE;


        if ((err = skb_cow_data(skb, 0, &trailer)) < 0)
                goto out;
        nfrags = err;

        ah = (struct ip_auth_hdr *)skb->data;
        iph = ip_hdr(skb);
        ihl = ip_hdrlen(skb);

        if (x->props.flags & XFRM_STATE_ESN) {
                sglists = 1;
                seqhi_len = sizeof(*seqhi);
        }

        work_iph = ah_alloc_tmp(ahash, nfrags + sglists, ihl +
                                ahp->icv_trunc_len + seqhi_len);
        if (!work_iph) {
                err = -ENOMEM;
                goto out;
        }

        seqhi = (__be32 *)((char *)work_iph + ihl);
        auth_data = ah_tmp_auth(seqhi, seqhi_len);
        icv = ah_tmp_icv(ahash, auth_data, ahp->icv_trunc_len);
        req = ah_tmp_req(ahash, icv);
        sg = ah_req_sg(ahash, req);
        seqhisg = sg + nfrags;

        memcpy(work_iph, iph, ihl);
        memcpy(auth_data, ah->auth_data, ahp->icv_trunc_len);
        memset(ah->auth_data, 0, ahp->icv_trunc_len);

        iph->ttl = 0;
        iph->tos = 0;
        iph->frag_off = 0;
        iph->check = 0;
        if (ihl > sizeof(*iph)) {
                __be32 dummy;
                err = ip_clear_mutable_options(iph, &dummy);
                if (err)
                        goto out_free;
        }

        skb_push(skb, ihl);

        sg_init_table(sg, nfrags + sglists);
        err = skb_to_sgvec_nomark(skb, sg, 0, skb->len);
        if (unlikely(err < 0))
                goto out_free;

        if (x->props.flags & XFRM_STATE_ESN) {
                /* Attach seqhi sg right after packet payload */
                *seqhi = XFRM_SKB_CB(skb)->seq.input.hi;
                sg_set_buf(seqhisg, seqhi, seqhi_len);
        }
        ahash_request_set_crypt(req, sg, icv, skb->len + seqhi_len);
        ahash_request_set_callback(req, 0, ah_input_done, skb);

        AH_SKB_CB(skb)->tmp = work_iph;

        err = crypto_ahash_digest(req);
        if (err) {
                if (err == -EINPROGRESS)
                        goto out;

                goto out_free;
        }

        err = crypto_memneq(icv, auth_data, ahp->icv_trunc_len) ? -EBADMSG : 0;
        if (err)
                goto out_free;

        skb->network_header += ah_hlen;
        memcpy(skb_network_header(skb), work_iph, ihl);
        __skb_pull(skb, ah_hlen + ihl);
        if (x->props.mode == XFRM_MODE_TUNNEL)
                skb_reset_transport_header(skb);
        else
                skb_set_transport_header(skb, -ihl);

        err = nexthdr;

out_free:
        kfree (work_iph);
out:
        return err;
}

static int ah4_err(struct sk_buff *skb, u32 info)
{
        struct net *net = dev_net(skb->dev);
        const struct iphdr *iph = (const struct iphdr *)skb->data;
        struct ip_auth_hdr *ah = (struct ip_auth_hdr *)(skb->data+(iph->ihl<<2));
        struct xfrm_state *x;

        switch (icmp_hdr(skb)->type) {
        case ICMP_DEST_UNREACH:
                if (icmp_hdr(skb)->code != ICMP_FRAG_NEEDED)
                        return 0;
        case ICMP_REDIRECT:
                break;
        default:
                return 0;
        }

        x = xfrm_state_lookup(net, skb->mark, (const xfrm_address_t *)&iph->daddr,
                              ah->spi, IPPROTO_AH, AF_INET);
        if (!x)
                return 0;

        if (icmp_hdr(skb)->type == ICMP_DEST_UNREACH)
                ipv4_update_pmtu(skb, net, info, 0, 0, IPPROTO_AH, 0);
        else
                ipv4_redirect(skb, net, 0, 0, IPPROTO_AH, 0);
        xfrm_state_put(x);

        return 0;
}

static int ah_init_state(struct xfrm_state *x)
{
        struct ah_data *ahp = NULL;
        struct xfrm_algo_desc *aalg_desc;
        struct crypto_ahash *ahash;

        if (!x->aalg)
                goto error;

        if (x->encap)
                goto error;

        ahp = kzalloc(sizeof(*ahp), GFP_KERNEL);
        if (!ahp)
                return -ENOMEM;

        ahash = crypto_alloc_ahash(x->aalg->alg_name, 0, 0);
        if (IS_ERR(ahash))
                goto error;

        ahp->ahash = ahash;
        if (crypto_ahash_setkey(ahash, x->aalg->alg_key,
                                (x->aalg->alg_key_len + 7) / 8))
                goto error;

        /*
         * Lookup the algorithm description maintained by xfrm_algo,
         * verify crypto transform properties, and store information
         * we need for AH processing.  This lookup cannot fail here
         * after a successful crypto_alloc_ahash().
         */
        aalg_desc = xfrm_aalg_get_byname(x->aalg->alg_name, 0);
        BUG_ON(!aalg_desc);

        if (aalg_desc->uinfo.auth.icv_fullbits/8 !=
            crypto_ahash_digestsize(ahash)) {
                pr_info("%s: %s digestsize %u != %hu\n",
                        __func__, x->aalg->alg_name,
                        crypto_ahash_digestsize(ahash),
                        aalg_desc->uinfo.auth.icv_fullbits / 8);
                goto error;
        }

        ahp->icv_full_len = aalg_desc->uinfo.auth.icv_fullbits/8;
        ahp->icv_trunc_len = x->aalg->alg_trunc_len/8;

        if (x->props.flags & XFRM_STATE_ALIGN4)
                x->props.header_len = XFRM_ALIGN4(sizeof(struct ip_auth_hdr) +
                                                  ahp->icv_trunc_len);
        else
                x->props.header_len = XFRM_ALIGN8(sizeof(struct ip_auth_hdr) +
                                                  ahp->icv_trunc_len);
        if (x->props.mode == XFRM_MODE_TUNNEL)
                x->props.header_len += sizeof(struct iphdr);
        x->data = ahp;

        return 0;

error:
        if (ahp) {
                crypto_free_ahash(ahp->ahash);
                kfree(ahp);
        }
        return -EINVAL;
}

static void ah_destroy(struct xfrm_state *x)
{
        struct ah_data *ahp = x->data;

        if (!ahp)
                return;

        crypto_free_ahash(ahp->ahash);
        kfree(ahp);
}

static int ah4_rcv_cb(struct sk_buff *skb, int err)
{
        return 0;
}

static const struct xfrm_type ah_type =
{
        .description    = "AH4",
        .owner          = THIS_MODULE,
        .proto          = IPPROTO_AH,
        .flags          = XFRM_TYPE_REPLAY_PROT,
        .init_state     = ah_init_state,
        .destructor     = ah_destroy,
        .input          = ah_input,
        .output         = ah_output
};

static struct xfrm4_protocol ah4_protocol = {
        .handler        =       xfrm4_rcv,
        .input_handler  =       xfrm_input,
        .cb_handler     =       ah4_rcv_cb,
        .err_handler    =       ah4_err,
        .priority       =       0,
};

static int __init ah4_init(void)
{
        if (xfrm_register_type(&ah_type, AF_INET) < 0) {
                pr_info("%s: can't add xfrm type\n", __func__);
                return -EAGAIN;
        }
        if (xfrm4_protocol_register(&ah4_protocol, IPPROTO_AH) < 0) {
                pr_info("%s: can't add protocol\n", __func__);
                xfrm_unregister_type(&ah_type, AF_INET);
                return -EAGAIN;
        }
        return 0;
}

static void __exit ah4_fini(void)
{
        if (xfrm4_protocol_deregister(&ah4_protocol, IPPROTO_AH) < 0)
                pr_info("%s: can't remove protocol\n", __func__);
        if (xfrm_unregister_type(&ah_type, AF_INET) < 0)
                pr_info("%s: can't remove xfrm type\n", __func__);
}

module_init(ah4_init);
module_exit(ah4_fini);
MODULE_LICENSE("GPL");
MODULE_ALIAS_XFRM_TYPE(AF_INET, XFRM_PROTO_AH);