// SPDX-License-Identifier: GPL-2.0-only

  #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, IPPROTO_AH);

  	else

  		ipv4_redirect(skb, net, 0, IPPROTO_AH);

  	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
  ",
  			__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
  ", __func__);

  		return -EAGAIN;
  	}

  	if (xfrm4_protocol_register(&ah4_protocol, IPPROTO_AH) < 0) {

  		pr_info("%s: can't add protocol
  ", __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
  ", __func__);

  	xfrm_unregister_type(&ah_type, AF_INET);

  }
  
  module_init(ah4_init);
  module_exit(ah4_fini);
  MODULE_LICENSE("GPL");

  MODULE_ALIAS_XFRM_TYPE(AF_INET, XFRM_PROTO_AH);