/*
   * Copyright (C)2002 USAGI/WIDE Project
   *
   * 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.
   *
   * This program is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   * GNU General Public License for more details.
   *
   * You should have received a copy of the GNU General Public License
   * along with this program; if not, see <http://www.gnu.org/licenses/>.
   *
   * Authors
   *
   *	Mitsuru KANDA @USAGI       : IPv6 Support
   * 	Kazunori MIYAZAWA @USAGI   :
   * 	Kunihiro Ishiguro <kunihiro@ipinfusion.com>
   *
   * 	This file is derived from net/ipv4/ah.c.
   */
  
  #define pr_fmt(fmt) "IPv6: " fmt
  
  #include <crypto/hash.h>
  #include <linux/module.h>
  #include <linux/slab.h>
  #include <net/ip.h>
  #include <net/ah.h>
  #include <linux/crypto.h>
  #include <linux/pfkeyv2.h>
  #include <linux/string.h>
  #include <linux/scatterlist.h>
  #include <net/ip6_route.h>
  #include <net/icmp.h>
  #include <net/ipv6.h>
  #include <net/protocol.h>
  #include <net/xfrm.h>
  
  #define IPV6HDR_BASELEN 8
  
  struct tmp_ext {
  #if IS_ENABLED(CONFIG_IPV6_MIP6)
  		struct in6_addr saddr;
  #endif
  		struct in6_addr daddr;
  		char hdrs[0];
  };
  
  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 struct tmp_ext *ah_tmp_ext(void *base)
  {
  	return base + IPV6HDR_BASELEN;
  }
  
  static inline u8 *ah_tmp_auth(u8 *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));
  }
  
  static bool zero_out_mutable_opts(struct ipv6_opt_hdr *opthdr)
  {
  	u8 *opt = (u8 *)opthdr;
  	int len = ipv6_optlen(opthdr);
  	int off = 0;
  	int optlen = 0;
  
  	off += 2;
  	len -= 2;
  
  	while (len > 0) {
  
  		switch (opt[off]) {
  
  		case IPV6_TLV_PAD1:
  			optlen = 1;
  			break;
  		default:
  			if (len < 2)
  				goto bad;
  			optlen = opt[off+1]+2;
  			if (len < optlen)
  				goto bad;
  			if (opt[off] & 0x20)
  				memset(&opt[off+2], 0, opt[off+1]);
  			break;
  		}
  
  		off += optlen;
  		len -= optlen;
  	}
  	if (len == 0)
  		return true;
  
  bad:
  	return false;
  }
  
  #if IS_ENABLED(CONFIG_IPV6_MIP6)
  /**
   *	ipv6_rearrange_destopt - rearrange IPv6 destination options header
   *	@iph: IPv6 header
   *	@destopt: destionation options header
   */
  static void ipv6_rearrange_destopt(struct ipv6hdr *iph, struct ipv6_opt_hdr *destopt)
  {
  	u8 *opt = (u8 *)destopt;
  	int len = ipv6_optlen(destopt);
  	int off = 0;
  	int optlen = 0;
  
  	off += 2;
  	len -= 2;
  
  	while (len > 0) {
  
  		switch (opt[off]) {
  
  		case IPV6_TLV_PAD1:
  			optlen = 1;
  			break;
  		default:
  			if (len < 2)
  				goto bad;
  			optlen = opt[off+1]+2;
  			if (len < optlen)
  				goto bad;
  
  			/* Rearrange the source address in @iph and the
  			 * addresses in home address option for final source.
  			 * See 11.3.2 of RFC 3775 for details.
  			 */
  			if (opt[off] == IPV6_TLV_HAO) {
  				struct in6_addr final_addr;
  				struct ipv6_destopt_hao *hao;
  
  				hao = (struct ipv6_destopt_hao *)&opt[off];
  				if (hao->length != sizeof(hao->addr)) {
  					net_warn_ratelimited("destopt hao: invalid header length: %u
  ",
  							     hao->length);
  					goto bad;
  				}
  				final_addr = hao->addr;
  				hao->addr = iph->saddr;
  				iph->saddr = final_addr;
  			}
  			break;
  		}
  
  		off += optlen;
  		len -= optlen;
  	}
  	/* Note: ok if len == 0 */
  bad:
  	return;
  }
  #else
  static void ipv6_rearrange_destopt(struct ipv6hdr *iph, struct ipv6_opt_hdr *destopt) {}
  #endif
  
  /**
   *	ipv6_rearrange_rthdr - rearrange IPv6 routing header
   *	@iph: IPv6 header
   *	@rthdr: routing header
   *
   *	Rearrange the destination address in @iph and the addresses in @rthdr
   *	so that they appear in the order they will at the final destination.
   *	See Appendix A2 of RFC 2402 for details.
   */
  static void ipv6_rearrange_rthdr(struct ipv6hdr *iph, struct ipv6_rt_hdr *rthdr)
  {
  	int segments, segments_left;
  	struct in6_addr *addrs;
  	struct in6_addr final_addr;
  
  	segments_left = rthdr->segments_left;
  	if (segments_left == 0)
  		return;
  	rthdr->segments_left = 0;
  
  	/* The value of rthdr->hdrlen has been verified either by the system
  	 * call if it is locally generated, or by ipv6_rthdr_rcv() for incoming
  	 * packets.  So we can assume that it is even and that segments is
  	 * greater than or equal to segments_left.
  	 *
  	 * For the same reason we can assume that this option is of type 0.
  	 */
  	segments = rthdr->hdrlen >> 1;
  
  	addrs = ((struct rt0_hdr *)rthdr)->addr;
  	final_addr = addrs[segments - 1];
  
  	addrs += segments - segments_left;
  	memmove(addrs + 1, addrs, (segments_left - 1) * sizeof(*addrs));
  
  	addrs[0] = iph->daddr;
  	iph->daddr = final_addr;
  }
  
  static int ipv6_clear_mutable_options(struct ipv6hdr *iph, int len, int dir)
  {
  	union {
  		struct ipv6hdr *iph;
  		struct ipv6_opt_hdr *opth;
  		struct ipv6_rt_hdr *rth;
  		char *raw;
  	} exthdr = { .iph = iph };
  	char *end = exthdr.raw + len;
  	int nexthdr = iph->nexthdr;
  
  	exthdr.iph++;
  
  	while (exthdr.raw < end) {
  		switch (nexthdr) {
  		case NEXTHDR_DEST:
  			if (dir == XFRM_POLICY_OUT)
  				ipv6_rearrange_destopt(iph, exthdr.opth);
  		case NEXTHDR_HOP:
  			if (!zero_out_mutable_opts(exthdr.opth)) {
  				LIMIT_NETDEBUG(
  					KERN_WARNING "overrun %sopts
  ",
  					nexthdr == NEXTHDR_HOP ?
  						"hop" : "dest");
  				return -EINVAL;
  			}
  			break;
  
  		case NEXTHDR_ROUTING:
  			ipv6_rearrange_rthdr(iph, exthdr.rth);
  			break;
  
  		default :
  			return 0;
  		}
  
  		nexthdr = exthdr.opth->nexthdr;
  		exthdr.raw += ipv6_optlen(exthdr.opth);
  	}
  
  	return 0;
  }
  
  static void ah6_output_done(struct crypto_async_request *base, int err)
  {
  	int extlen;
  	u8 *iph_base;
  	u8 *icv;
  	struct sk_buff *skb = base->data;
  	struct xfrm_state *x = skb_dst(skb)->xfrm;
  	struct ah_data *ahp = x->data;
  	struct ipv6hdr *top_iph = ipv6_hdr(skb);
  	struct ip_auth_hdr *ah = ip_auth_hdr(skb);
  	struct tmp_ext *iph_ext;
  
  	extlen = skb_network_header_len(skb) - sizeof(struct ipv6hdr);
  	if (extlen)
  		extlen += sizeof(*iph_ext);
  
  	iph_base = AH_SKB_CB(skb)->tmp;
  	iph_ext = ah_tmp_ext(iph_base);
  	icv = ah_tmp_icv(ahp->ahash, iph_ext, extlen);
  
  	memcpy(ah->auth_data, icv, ahp->icv_trunc_len);
  	memcpy(top_iph, iph_base, IPV6HDR_BASELEN);
  
  	if (extlen) {
  #if IS_ENABLED(CONFIG_IPV6_MIP6)
  		memcpy(&top_iph->saddr, iph_ext, extlen);
  #else
  		memcpy(&top_iph->daddr, iph_ext, extlen);
  #endif
  	}
  
  	kfree(AH_SKB_CB(skb)->tmp);
  	xfrm_output_resume(skb, err);
  }
  
  static int ah6_output(struct xfrm_state *x, struct sk_buff *skb)
  {
  	int err;
  	int nfrags;
  	int extlen;
  	u8 *iph_base;
  	u8 *icv;
  	u8 nexthdr;
  	struct sk_buff *trailer;
  	struct crypto_ahash *ahash;
  	struct ahash_request *req;
  	struct scatterlist *sg;
  	struct ipv6hdr *top_iph;
  	struct ip_auth_hdr *ah;
  	struct ah_data *ahp;
  	struct tmp_ext *iph_ext;
  
  	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));
  	extlen = skb_network_header_len(skb) - sizeof(struct ipv6hdr);
  	if (extlen)
  		extlen += sizeof(*iph_ext);
  
  	err = -ENOMEM;
  	iph_base = ah_alloc_tmp(ahash, nfrags, IPV6HDR_BASELEN + extlen);
  	if (!iph_base)
  		goto out;
  
  	iph_ext = ah_tmp_ext(iph_base);
  	icv = ah_tmp_icv(ahash, iph_ext, extlen);
  	req = ah_tmp_req(ahash, icv);
  	sg = ah_req_sg(ahash, req);
  
  	ah = ip_auth_hdr(skb);
  	memset(ah->auth_data, 0, ahp->icv_trunc_len);
  
  	top_iph = ipv6_hdr(skb);
  	top_iph->payload_len = htons(skb->len - sizeof(*top_iph));
  
  	nexthdr = *skb_mac_header(skb);
  	*skb_mac_header(skb) = IPPROTO_AH;
  
  	/* When there are no extension headers, we only need to save the first
  	 * 8 bytes of the base IP header.
  	 */
  	memcpy(iph_base, top_iph, IPV6HDR_BASELEN);
  
  	if (extlen) {
  #if IS_ENABLED(CONFIG_IPV6_MIP6)
  		memcpy(iph_ext, &top_iph->saddr, extlen);
  #else
  		memcpy(iph_ext, &top_iph->daddr, extlen);
  #endif
  		err = ipv6_clear_mutable_options(top_iph,
  						 extlen - sizeof(*iph_ext) +
  						 sizeof(*top_iph),
  						 XFRM_POLICY_OUT);
  		if (err)
  			goto out_free;
  	}
  
  	ah->nexthdr = nexthdr;
  
  	top_iph->priority    = 0;
  	top_iph->flow_lbl[0] = 0;
  	top_iph->flow_lbl[1] = 0;
  	top_iph->flow_lbl[2] = 0;
  	top_iph->hop_limit   = 0;
  
  	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);
  	skb_to_sgvec(skb, sg, 0, skb->len);
  
  	ahash_request_set_crypt(req, sg, icv, skb->len);
  	ahash_request_set_callback(req, 0, ah6_output_done, skb);
  
  	AH_SKB_CB(skb)->tmp = iph_base;
  
  	err = crypto_ahash_digest(req);
  	if (err) {
  		if (err == -EINPROGRESS)
  			goto out;
  
  		if (err == -EBUSY)
  			err = NET_XMIT_DROP;
  		goto out_free;
  	}
  
  	memcpy(ah->auth_data, icv, ahp->icv_trunc_len);
  	memcpy(top_iph, iph_base, IPV6HDR_BASELEN);
  
  	if (extlen) {
  #if IS_ENABLED(CONFIG_IPV6_MIP6)
  		memcpy(&top_iph->saddr, iph_ext, extlen);
  #else
  		memcpy(&top_iph->daddr, iph_ext, extlen);
  #endif
  	}
  
  out_free:
  	kfree(iph_base);
  out:
  	return err;
  }
  
  static void ah6_input_done(struct crypto_async_request *base, int err)
  {
  	u8 *auth_data;
  	u8 *icv;
  	u8 *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 hdr_len = skb_network_header_len(skb);
  	int ah_hlen = (ah->hdrlen + 2) << 2;
  
  	work_iph = AH_SKB_CB(skb)->tmp;
  	auth_data = ah_tmp_auth(work_iph, hdr_len);
  	icv = ah_tmp_icv(ahp->ahash, auth_data, ahp->icv_trunc_len);
  
  	err = memcmp(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, hdr_len);
  	__skb_pull(skb, ah_hlen + hdr_len);
  	if (x->props.mode == XFRM_MODE_TUNNEL)
  		skb_reset_transport_header(skb);
  	else
  		skb_set_transport_header(skb, -hdr_len);
  out:
  	kfree(AH_SKB_CB(skb)->tmp);
  	xfrm_input_resume(skb, err);
  }
  
  
  
  static int ah6_input(struct xfrm_state *x, struct sk_buff *skb)
  {
  	/*
  	 * Before process AH
  	 * [IPv6][Ext1][Ext2][AH][Dest][Payload]
  	 * |<-------------->| hdr_len
  	 *
  	 * To erase AH:
  	 * Keeping copy of cleared headers. After AH processing,
  	 * Moving the pointer of skb->network_header by using skb_pull as long
  	 * as AH header length. Then copy back the copy as long as hdr_len
  	 * If destination header following AH exists, copy it into after [Ext2].
  	 *
  	 * |<>|[IPv6][Ext1][Ext2][Dest][Payload]
  	 * There is offset of AH before IPv6 header after the process.
  	 */
  
  	u8 *auth_data;
  	u8 *icv;
  	u8 *work_iph;
  	struct sk_buff *trailer;
  	struct crypto_ahash *ahash;
  	struct ahash_request *req;
  	struct scatterlist *sg;
  	struct ip_auth_hdr *ah;
  	struct ipv6hdr *ip6h;
  	struct ah_data *ahp;
  	u16 hdr_len;
  	u16 ah_hlen;
  	int nexthdr;
  	int nfrags;
  	int err = -ENOMEM;
  
  	if (!pskb_may_pull(skb, sizeof(struct ip_auth_hdr)))
  		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;
  
  	hdr_len = skb_network_header_len(skb);
  	ah = (struct ip_auth_hdr *)skb->data;
  	ahp = x->data;
  	ahash = ahp->ahash;
  
  	nexthdr = ah->nexthdr;
  	ah_hlen = (ah->hdrlen + 2) << 2;
  
  	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;
  
  
  	if ((err = skb_cow_data(skb, 0, &trailer)) < 0)
  		goto out;
  	nfrags = err;
  
  	ah = (struct ip_auth_hdr *)skb->data;
  	ip6h = ipv6_hdr(skb);
  
  	skb_push(skb, hdr_len);
  
  	work_iph = ah_alloc_tmp(ahash, nfrags, hdr_len + ahp->icv_trunc_len);
  	if (!work_iph)
  		goto out;
  
  	auth_data = ah_tmp_auth(work_iph, hdr_len);
  	icv = ah_tmp_icv(ahash, auth_data, ahp->icv_trunc_len);
  	req = ah_tmp_req(ahash, icv);
  	sg = ah_req_sg(ahash, req);
  
  	memcpy(work_iph, ip6h, hdr_len);
  	memcpy(auth_data, ah->auth_data, ahp->icv_trunc_len);
  	memset(ah->auth_data, 0, ahp->icv_trunc_len);
  
  	if (ipv6_clear_mutable_options(ip6h, hdr_len, XFRM_POLICY_IN))
  		goto out_free;
  
  	ip6h->priority    = 0;
  	ip6h->flow_lbl[0] = 0;
  	ip6h->flow_lbl[1] = 0;
  	ip6h->flow_lbl[2] = 0;
  	ip6h->hop_limit   = 0;
  
  	sg_init_table(sg, nfrags);
  	skb_to_sgvec(skb, sg, 0, skb->len);
  
  	ahash_request_set_crypt(req, sg, icv, skb->len);
  	ahash_request_set_callback(req, 0, ah6_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 = memcmp(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, hdr_len);
  	__skb_pull(skb, ah_hlen + hdr_len);
  
  	if (x->props.mode == XFRM_MODE_TUNNEL)
  		skb_reset_transport_header(skb);
  	else
  		skb_set_transport_header(skb, -hdr_len);
  
  	err = nexthdr;
  
  out_free:
  	kfree(work_iph);
  out:
  	return err;
  }
  
  static void ah6_err(struct sk_buff *skb, struct inet6_skb_parm *opt,
  		    u8 type, u8 code, int offset, __be32 info)
  {
  	struct net *net = dev_net(skb->dev);
  	struct ipv6hdr *iph = (struct ipv6hdr*)skb->data;
  	struct ip_auth_hdr *ah = (struct ip_auth_hdr*)(skb->data+offset);
  	struct xfrm_state *x;
  
  	if (type != ICMPV6_PKT_TOOBIG &&
  	    type != NDISC_REDIRECT)
  		return;
  
  	x = xfrm_state_lookup(net, skb->mark, (xfrm_address_t *)&iph->daddr, ah->spi, IPPROTO_AH, AF_INET6);
  	if (!x)
  		return;
  
  	if (type == NDISC_REDIRECT)
  		ip6_redirect(skb, net, skb->dev->ifindex, 0);
  	else
  		ip6_update_pmtu(skb, net, info, 0, 0);
  	xfrm_state_put(x);
  }
  
  static int ah6_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 == NULL)
  		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_hash().
  	 */
  	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("AH: %s digestsize %u != %hu
  ",
  			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;
  
  	BUG_ON(ahp->icv_trunc_len > MAX_AH_AUTH_LEN);
  
  	x->props.header_len = XFRM_ALIGN8(sizeof(struct ip_auth_hdr) +
  					  ahp->icv_trunc_len);
  	switch (x->props.mode) {
  	case XFRM_MODE_BEET:
  	case XFRM_MODE_TRANSPORT:
  		break;
  	case XFRM_MODE_TUNNEL:
  		x->props.header_len += sizeof(struct ipv6hdr);
  		break;
  	default:
  		goto error;
  	}
  	x->data = ahp;
  
  	return 0;
  
  error:
  	if (ahp) {
  		crypto_free_ahash(ahp->ahash);
  		kfree(ahp);
  	}
  	return -EINVAL;
  }
  
  static void ah6_destroy(struct xfrm_state *x)
  {
  	struct ah_data *ahp = x->data;
  
  	if (!ahp)
  		return;
  
  	crypto_free_ahash(ahp->ahash);
  	kfree(ahp);
  }
  
  static const struct xfrm_type ah6_type =
  {
  	.description	= "AH6",
  	.owner		= THIS_MODULE,
  	.proto	     	= IPPROTO_AH,
  	.flags		= XFRM_TYPE_REPLAY_PROT,
  	.init_state	= ah6_init_state,
  	.destructor	= ah6_destroy,
  	.input		= ah6_input,
  	.output		= ah6_output,
  	.hdr_offset	= xfrm6_find_1stfragopt,
  };
  
  static const struct inet6_protocol ah6_protocol = {
  	.handler	=	xfrm6_rcv,
  	.err_handler	=	ah6_err,
  	.flags		=	INET6_PROTO_NOPOLICY,
  };
  
  static int __init ah6_init(void)
  {
  	if (xfrm_register_type(&ah6_type, AF_INET6) < 0) {
  		pr_info("%s: can't add xfrm type
  ", __func__);
  		return -EAGAIN;
  	}
  
  	if (inet6_add_protocol(&ah6_protocol, IPPROTO_AH) < 0) {
  		pr_info("%s: can't add protocol
  ", __func__);
  		xfrm_unregister_type(&ah6_type, AF_INET6);
  		return -EAGAIN;
  	}
  
  	return 0;
  }
  
  static void __exit ah6_fini(void)
  {
  	if (inet6_del_protocol(&ah6_protocol, IPPROTO_AH) < 0)
  		pr_info("%s: can't remove protocol
  ", __func__);
  
  	if (xfrm_unregister_type(&ah6_type, AF_INET6) < 0)
  		pr_info("%s: can't remove xfrm type
  ", __func__);
  
  }
  
  module_init(ah6_init);
  module_exit(ah6_fini);
  
  MODULE_LICENSE("GPL");
  MODULE_ALIAS_XFRM_TYPE(AF_INET6, XFRM_PROTO_AH);