/*
 * esp_decrypt.c : IPSec ESP decrypt node
 *
 * Copyright (c) 2015 Cisco and/or its affiliates.
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at:
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include <vnet/vnet.h>
#include <vnet/api_errno.h>
#include <vnet/ip/ip.h>
#include <vnet/l2/l2_input.h>

#include <vnet/ipsec/ipsec.h>
#include <vnet/ipsec/esp.h>
#include <vnet/ipsec/ipsec_io.h>
#include <vnet/ipsec/ipsec_tun.h>

#include <vnet/gre/gre.h>

#define foreach_esp_decrypt_next                \
_(DROP, "error-drop")                           \
_(IP4_INPUT, "ip4-input-no-checksum")           \
_(IP6_INPUT, "ip6-input")                       \
_(L2_INPUT, "l2-input")                         \
_(HANDOFF, "handoff")

#define _(v, s) ESP_DECRYPT_NEXT_##v,
typedef enum
{
  foreach_esp_decrypt_next
#undef _
    ESP_DECRYPT_N_NEXT,
} esp_decrypt_next_t;


#define foreach_esp_decrypt_error                               \
 _(RX_PKTS, "ESP pkts received")                                \
 _(DECRYPTION_FAILED, "ESP decryption failed")                  \
 _(INTEG_ERROR, "Integrity check failed")                       \
 _(CRYPTO_ENGINE_ERROR, "crypto engine error (packet dropped)") \
 _(REPLAY, "SA replayed packet")                                \
 _(RUNT, "undersized packet")                                   \
 _(NO_BUFFERS, "no buffers (packet dropped)")                   \
 _(OVERSIZED_HEADER, "buffer with oversized header (dropped)")  \
 _(NO_TAIL_SPACE, "no enough buffer tail space (dropped)")      \
 _(TUN_NO_PROTO, "no tunnel protocol")                          \
 _(UNSUP_PAYLOAD, "unsupported payload")                        \


typedef enum
{
#define _(sym,str) ESP_DECRYPT_ERROR_##sym,
  foreach_esp_decrypt_error
#undef _
    ESP_DECRYPT_N_ERROR,
} esp_decrypt_error_t;

static char *esp_decrypt_error_strings[] = {
#define _(sym,string) string,
  foreach_esp_decrypt_error
#undef _
};

typedef struct
{
  u32 seq;
  u32 sa_seq;
  u32 sa_seq_hi;
  ipsec_crypto_alg_t crypto_alg;
  ipsec_integ_alg_t integ_alg;
} esp_decrypt_trace_t;

/* packet trace format function */
static u8 *
format_esp_decrypt_trace (u8 * s, va_list * args)
{
  CLIB_UNUSED (vlib_main_t * vm) = va_arg (*args, vlib_main_t *);
  CLIB_UNUSED (vlib_node_t * node) = va_arg (*args, vlib_node_t *);
  esp_decrypt_trace_t *t = va_arg (*args, esp_decrypt_trace_t *);

  s =
    format (s,
	    "esp: crypto %U integrity %U pkt-seq %d sa-seq %u sa-seq-hi %u",
	    format_ipsec_crypto_alg, t->crypto_alg, format_ipsec_integ_alg,
	    t->integ_alg, t->seq, t->sa_seq, t->sa_seq_hi);
  return s;
}

typedef struct
{
  vlib_buffer_t *lb;
  union
  {
    struct
    {
      u8 icv_sz;
      u8 iv_sz;
      ipsec_sa_flags_t flags;
      u32 sa_index;
    };
    u64 sa_data;
  };

  u32 seq;
  u32 free_buffer_index;
  i16 current_data;
  i16 current_length;
  u16 hdr_sz;
  u8 icv_removed;
  u8 __unused;
} esp_decrypt_packet_data_t;

STATIC_ASSERT_SIZEOF (esp_decrypt_packet_data_t, 4 * sizeof (u64));

#define ESP_ENCRYPT_PD_F_FD_TRANSPORT (1 << 2)

static_always_inline void
esp_process_ops (vlib_main_t * vm, vlib_node_runtime_t * node,
		 vnet_crypto_op_t * ops, vlib_buffer_t * b[], u16 * nexts,
		 int e)
{
  vnet_crypto_op_t *op = ops;
  u32 n_fail, n_ops = vec_len (ops);

  if (n_ops == 0)
    return;

  n_fail = n_ops - vnet_crypto_process_ops (vm, op, n_ops);

  while (n_fail)
    {
      ASSERT (op - ops < n_ops);
      if (op->status != VNET_CRYPTO_OP_STATUS_COMPLETED)
	{
	  u32 err, bi = op->user_data;
	  if (op->status == VNET_CRYPTO_OP_STATUS_FAIL_BAD_HMAC)
	    err = e;
	  else
	    err = ESP_DECRYPT_ERROR_CRYPTO_ENGINE_ERROR;
	  b[bi]->error = node->errors[err];
	  nexts[bi] = ESP_DECRYPT_NEXT_DROP;
	  n_fail--;
	}
      op++;
    }
}

static_always_inline void
esp_process_chained_ops (vlib_main_t * vm, vlib_node_runtime_t * node,
			 vnet_crypto_op_t * ops, vlib_buffer_t * b[],
			 u16 * nexts, vnet_crypto_op_chunk_t * chunks, int e)
{

  vnet_crypto_op_t *op = ops;
  u32 n_fail, n_ops = vec_len (ops);

  if (n_ops == 0)
    return;

  n_fail = n_ops - vnet_crypto_process_chained_ops (vm, op, chunks, n_ops);

  while (n_fail)
    {
      ASSERT (op - ops < n_ops);
      if (op->status != VNET_CRYPTO_OP_STATUS_COMPLETED)
	{
	  u32 err, bi = op->user_data;
	  if (op->status == VNET_CRYPTO_OP_STATUS_FAIL_BAD_HMAC)
	    err = e;
	  else
	    err = ESP_DECRYPT_ERROR_CRYPTO_ENGINE_ERROR;
	  b[bi]->error = node->errors[err];
	  nexts[bi] = ESP_DECRYPT_NEXT_DROP;
	  n_fail--;
	}
      op++;
    }
}

always_inline void
esp_remove_tail (vlib_main_t * vm, vlib_buffer_t * b, vlib_buffer_t * last,
		 u16 tail)
{
  vlib_buffer_t *before_last = b;

  if (last->current_length > tail)
    {
      last->current_length -= tail;
      return;
    }
  ASSERT (b->flags & VLIB_BUFFER_NEXT_PRESENT);

  while (b->flags & VLIB_BUFFER_NEXT_PRESENT)
    {
      before_last = b;
      b = vlib_get_buffer (vm, b->next_buffer);
    }
  before_last->current_length -= tail - last->current_length;
  vlib_buffer_free_one (vm, before_last->next_buffer);
  before_last->flags &= ~VLIB_BUFFER_NEXT_PRESENT;
}

/* ICV is splitted in last two buffers so move it to the last buffer and
   return pointer to it */
static_always_inline u8 *
esp_move_icv (vlib_main_t * vm, vlib_buffer_t * first,
	      esp_decrypt_packet_data_t * pd, u16 icv_sz)
{
  vlib_buffer_t *before_last, *bp;
  u16 last_sz = pd->lb->current_length;
  u16 first_sz = icv_sz - last_sz;

  bp = before_last = first;
  while (bp->flags & VLIB_BUFFER_NEXT_PRESENT)
    {
      before_last = bp;
      bp = vlib_get_buffer (vm, bp->next_buffer);
    }

  u8 *lb_curr = vlib_buffer_get_current (pd->lb);
  memmove (lb_curr + first_sz, lb_curr, last_sz);
  clib_memcpy_fast (lb_curr, vlib_buffer_get_tail (before_last) - first_sz,
		    first_sz);
  before_last->current_length -= first_sz;
  pd->lb = before_last;
  pd->icv_removed = 1;
  pd->free_buffer_index = before_last->next_buffer;
  before_last->flags &= ~VLIB_BUFFER_NEXT_PRESENT;
  return lb_curr;
}

always_inline uword
esp_decrypt_inline (vlib_main_t * vm,
		    vlib_node_runtime_t * node, vlib_frame_t * from_frame,
		    int is_ip6, int is_tun)
{
  ipsec_main_t *im = &ipsec_main;
  u32 thread_index = vm->thread_index;
  u16 buffer_data_size = vlib_buffer_get_default_data_size (vm);
  u16 len;
  ipsec_per_thread_data_t *ptd = vec_elt_at_index (im->ptd, thread_index);
  u32 *from = vlib_frame_vector_args (from_frame);
  u32 n_left = from_frame->n_vectors;
  vlib_buffer_t *bufs[VLIB_FRAME_SIZE], **b = bufs;
  u16 nexts[VLIB_FRAME_SIZE], *next = nexts;
  esp_decrypt_packet_data_t pkt_data[VLIB_FRAME_SIZE], *pd = pkt_data;
  esp_decrypt_packet_data_t cpd = { };
  u32 current_sa_index = ~0, current_sa_bytes = 0, current_sa_pkts = 0;
  const u8 esp_sz = sizeof (esp_header_t);
  ipsec_sa_t *sa0 = 0;
  vnet_crypto_op_chunk_t *ch;
  vnet_crypto_op_t **crypto_ops = &ptd->crypto_ops;
  vnet_crypto_op_t **integ_ops = &ptd->integ_ops;

  vlib_get_buffers (vm, from, b, n_left);
  vec_reset_length (ptd->crypto_ops);
  vec_reset_length (ptd->integ_ops);
  vec_reset_length (ptd->chained_crypto_ops);
  vec_reset_length (ptd->chained_integ_ops);
  vec_reset_length (ptd->chunks);
  clib_memset_u16 (nexts, -1, n_left);

  while (n_left > 0)
    {
      u8 *payload;

      if (n_left > 2)
	{
	  u8 *p;
	  vlib_prefetch_buffer_header (b[2], LOAD);
	  p = vlib_buffer_get_current (b[1]);
	  CLIB_PREFETCH (p, CLIB_CACHE_LINE_BYTES, LOAD);
	  p -= CLIB_CACHE_LINE_BYTES;
	  CLIB_PREFETCH (p, CLIB_CACHE_LINE_BYTES, LOAD);
	}

      u32 n_bufs = vlib_buffer_chain_linearize (vm, b[0]);
      if (n_bufs == 0)
	{
	  b[0]->error = node->errors[ESP_DECRYPT_ERROR_NO_BUFFERS];
	  next[0] = ESP_DECRYPT_NEXT_DROP;
	  goto next;
	}

      if (vnet_buffer (b[0])->ipsec.sad_index != current_sa_index)
	{
	  if (current_sa_pkts)
	    vlib_increment_combined_counter (&ipsec_sa_counters, thread_index,
					     current_sa_index,
					     current_sa_pkts,
					     current_sa_bytes);
	  current_sa_bytes = current_sa_pkts = 0;

	  current_sa_index = vnet_buffer (b[0])->ipsec.sad_index;
	  sa0 = pool_elt_at_index (im->sad, current_sa_index);
	  cpd.icv_sz = sa0->integ_icv_size;
	  cpd.iv_sz = sa0->crypto_iv_size;
	  cpd.flags = sa0->flags;
	  cpd.sa_index = current_sa_index;
	}

      if (PREDICT_FALSE (~0 == sa0->decrypt_thread_index))
	{
	  /* this is the first packet to use this SA, claim the SA
	   * for this thread. this could happen simultaneously on
	   * another thread */
	  clib_atomic_cmp_and_swap (&sa0->decrypt_thread_index, ~0,
				    ipsec_sa_assign_thread (thread_index));
	}

      if (PREDICT_TRUE (thread_index != sa0->decrypt_thread_index))
	{
	  next[0] = ESP_DECRYPT_NEXT_HANDOFF;
	  goto next;
	}

      /* store packet data for next round for easier prefetch */
      pd->sa_data = cpd.sa_data;
      pd->current_data = b[0]->current_data;
      pd->current_length = b[0]->current_length;
      pd->hdr_sz = pd->current_data - vnet_buffer (b[0])->l3_hdr_offset;
      payload = b[0]->data + pd->current_data;
      pd->seq = clib_host_to_net_u32 (((esp_header_t *) payload)->seq);
      pd->free_buffer_index = 0;
      pd->icv_removed = 0;

      pd->lb = b[0];
      if (n_bufs > 1)
	{
	  /* find last buffer in the chain */
	  while (pd->lb->flags & VLIB_BUFFER_NEXT_PRESENT)
	    pd->lb = vlib_get_buffer (vm, pd->lb->next_buffer);

	  crypto_ops = &ptd->chained_crypto_ops;
	  integ_ops = &ptd->chained_integ_ops;
	}
      pd->current_length = b[0]->current_length;

      /* we need 4 extra bytes for HMAC calculation when ESN are used */
      /* Chained buffers can process ESN as a separate chunk */
      if (pd->lb == b[0] && ipsec_sa_is_set_USE_ESN (sa0) && cpd.icv_sz &&
	  (pd->lb->current_data + pd->lb->current_length + 4
	   > buffer_data_size))
	{
	  b[0]->error = node->errors[ESP_DECRYPT_ERROR_NO_TAIL_SPACE];
	  next[0] = ESP_DECRYPT_NEXT_DROP;
	  goto next;
	}

      /* anti-reply check */
      if (ipsec_sa_anti_replay_check (sa0, pd->seq))
	{
	  b[0]->error = node->errors[ESP_DECRYPT_ERROR_REPLAY];
	  next[0] = ESP_DECRYPT_NEXT_DROP;
	  goto next;
	}

      if (pd->current_length < cpd.icv_sz + esp_sz + cpd.iv_sz)
	{
	  b[0]->error = node->errors[ESP_DECRYPT_ERROR_RUNT];
	  next[0] = ESP_DECRYPT_NEXT_DROP;
	  goto next;
	}

      len = pd->current_length - cpd.icv_sz;
      current_sa_pkts += 1;
      current_sa_bytes += vlib_buffer_length_in_chain (vm, b[0]);

      if (PREDICT_TRUE (sa0->integ_op_id != VNET_CRYPTO_OP_NONE))
	{
	  vnet_crypto_op_t *op;
	  vec_add2_aligned (integ_ops[0], op, 1, CLIB_CACHE_LINE_BYTES);

	  vnet_crypto_op_init (op, sa0->integ_op_id);
	  op->key_index = sa0->integ_key_index;
	  op->src = payload;
	  op->flags = VNET_CRYPTO_OP_FLAG_HMAC_CHECK;
	  op->user_data = b - bufs;
	  op->digest = payload + len;
	  op->digest_len = cpd.icv_sz;
	  op->len = len;

	  if (pd->lb != b[0])
	    {
	      /* buffer is chained */
	      vlib_buffer_t *cb = b[0];
	      op->flags |= VNET_CRYPTO_OP_FLAG_CHAINED_BUFFERS;
	      op->chunk_index = vec_len (ptd->chunks);

	      if (pd->lb->current_length < cpd.icv_sz)
		op->digest = esp_move_icv (vm, b[0], pd, cpd.icv_sz);
	      else
		op->digest = vlib_buffer_get_tail (pd->lb) - cpd.icv_sz;

	      vec_add2 (ptd->chunks, ch, 1);
	      ch->len = pd->current_length;
	      ch->src = payload;
	      cb = vlib_get_buffer (vm, cb->next_buffer);
	      op->n_chunks = 1;
	      while (1)
		{
		  vec_add2 (ptd->chunks, ch, 1);
		  op->n_chunks += 1;
		  ch->src = vlib_buffer_get_current (cb);
		  if (pd->lb == cb)
		    {
		      if (pd->icv_removed)
			ch->len = cb->current_length;
		      else
			ch->len = cb->current_length - cpd.icv_sz;
		      if (ipsec_sa_is_set_USE_ESN (sa0))
			{
			  u32 seq_hi = clib_host_to_net_u32 (sa0->seq_hi);
			  u8 tmp[ESP_MAX_ICV_SIZE], sz = sizeof (sa0->seq_hi);
			  u8 *esn;
			  vlib_buffer_t *tmp_b;
			  u16 space_left = vlib_buffer_space_left_at_end
			    (vm, pd->lb);
			  if (space_left < sz)
			    {
			      if (pd->icv_removed)
				{
				  /* use pre-data area from the last bufer
				     that was removed from the chain */
				  tmp_b =
				    vlib_get_buffer (vm,
						     pd->free_buffer_index);
				  esn = tmp_b->data - sz;
				}
			      else
				{
				  /* no space, need to allocate new buffer */
				  u32 tmp_bi = 0;
				  vlib_buffer_alloc (vm, &tmp_bi, 1);
				  tmp_b = vlib_get_buffer (vm, tmp_bi);
				  esn = tmp_b->data;
				  pd->free_buffer_index = tmp_bi;
				}
			      clib_memcpy_fast (esn, &seq_hi, sz);

			      vec_add2 (ptd->chunks, ch, 1);
			      op->n_chunks += 1;
			      ch->src = esn;
			      ch->len = sz;
			    }
			  else
			    {
			      if (pd->icv_removed)
				{
				  clib_memcpy_fast (vlib_buffer_get_tail
						    (pd->lb), &seq_hi, sz);
				}
			      else
				{
				  clib_memcpy_fast (tmp, op->digest,
						    ESP_MAX_ICV_SIZE);
				  clib_memcpy_fast (op->digest, &seq_hi, sz);
				  clib_memcpy_fast (op->digest + sz, tmp,
						    ESP_MAX_ICV_SIZE);
				  op->digest += sz;
				}
			      ch->len += sz;
			    }
			}
		    }
		  else
		    ch->len = cb->current_length;

		  if (!(cb->flags & VLIB_BUFFER_NEXT_PRESENT))
		    break;

		  cb = vlib_get_buffer (vm, cb->next_buffer);
		}
	    }
	  else if (ipsec_sa_is_set_USE_ESN (sa0))
	    {
	      /* shift ICV by 4 bytes to insert ESN */
	      u32 seq_hi = clib_host_to_net_u32 (sa0->seq_hi);
	      u8 tmp[ESP_MAX_ICV_SIZE], sz = sizeof (sa0->seq_hi);
	      clib_memcpy_fast (tmp, payload + len, ESP_MAX_ICV_SIZE);
	      clib_memcpy_fast (payload + len, &seq_hi, sz);
	      clib_memcpy_fast (payload + len + sz, tmp, ESP_MAX_ICV_SIZE);
	      op->len += sz;
	      op->digest += sz;
	    }
	}

      payload += esp_sz;
      len -= esp_sz;

      if (sa0->crypto_dec_op_id != VNET_CRYPTO_OP_NONE)
	{
	  vnet_crypto_op_t *op;
	  vec_add2_aligned (crypto_ops[0], op, 1, CLIB_CACHE_LINE_BYTES);
	  vnet_crypto_op_init (op, sa0->crypto_dec_op_id);
	  op->key_index = sa0->crypto_key_index;
	  op->iv = payload;

	  if (ipsec_sa_is_set_IS_AEAD (sa0))
	    {
	      esp_header_t *esp0;
	      esp_aead_t *aad;
	      u8 *scratch;

	      /*
	       * construct the AAD and the nonce (Salt || IV) in a scratch
	       * space in front of the IP header.
	       */
	      scratch = payload - esp_sz;
	      esp0 = (esp_header_t *) (scratch);

	      scratch -= (sizeof (*aad) + pd->hdr_sz);
	      op->aad = scratch;

	      esp_aad_fill (op, esp0, sa0);

	      /*
	       * we don't need to refer to the ESP header anymore so we
	       * can overwrite it with the salt and use the IV where it is
	       * to form the nonce = (Salt + IV)
	       */
	      op->iv -= sizeof (sa0->salt);
	      clib_memcpy_fast (op->iv, &sa0->salt, sizeof (sa0->salt));

	      op->tag = payload + len;
	      op->tag_len = 16;
	    }
	  op->src = op->dst = payload += cpd.iv_sz;
	  op->len = len - cpd.iv_sz;
	  op->user_data = b - bufs;

	  if (pd->lb != b[0])
	    {
	      /* buffer is chained */
	      vlib_buffer_t *cb = b[0];
	      op->flags |= VNET_CRYPTO_OP_FLAG_CHAINED_BUFFERS;
	      op->chunk_index = vec_len (ptd->chunks);
	      vec_add2 (ptd->chunks, ch, 1);
	      ch->len = len - cpd.iv_sz + cpd.icv_sz;
	      ch->src = ch->dst = payload;
	      cb = vlib_get_buffer (vm, cb->next_buffer);
	      op->n_chunks = 1;

	      while (1)
		{
		  vec_add2 (ptd->chunks, ch, 1);
		  op->n_chunks += 1;
		  ch->src = ch->dst = vlib_buffer_get_current (cb);
		  if (pd->lb == cb)
		    {
		      if (ipsec_sa_is_set_IS_AEAD (sa0))
			{
			  if (pd->lb->current_length < cpd.icv_sz)
			    {
			      op->tag =
				esp_move_icv (vm, b[0], pd, cpd.icv_sz);

			      /* this chunk does not contain crypto data */
			      op->n_chunks -= 1;

			      /* and fix previous chunk's length as it might have
			         been changed */
			      ASSERT (op->n_chunks > 0);
			      ch[-1].len = pd->lb->current_length;
			      break;
			    }
			  else
			    op->tag =
			      vlib_buffer_get_tail (pd->lb) - cpd.icv_sz;
			}

		      if (pd->icv_removed)
			ch->len = cb->current_length;
		      else
			ch->len = cb->current_length - cpd.icv_sz;
		    }
		  else
		    ch->len = cb->current_length;

		  if (!(cb->flags & VLIB_BUFFER_NEXT_PRESENT))
		    break;

		  cb = vlib_get_buffer (vm, cb->next_buffer);
		}
	    }
	}

      /* next */
    next:
      n_left -= 1;
      next += 1;
      pd += 1;
      b += 1;
    }

  if (PREDICT_TRUE (~0 != current_sa_index))
    vlib_increment_combined_counter (&ipsec_sa_counters, thread_index,
				     current_sa_index, current_sa_pkts,
				     current_sa_bytes);

  esp_process_ops (vm, node, ptd->integ_ops, bufs, nexts,
		   ESP_DECRYPT_ERROR_INTEG_ERROR);
  esp_process_chained_ops (vm, node, ptd->chained_integ_ops, bufs, nexts,
			   ptd->chunks, ESP_DECRYPT_ERROR_INTEG_ERROR);

  esp_process_ops (vm, node, ptd->crypto_ops, bufs, nexts,
		   ESP_DECRYPT_ERROR_DECRYPTION_FAILED);
  esp_process_chained_ops (vm, node, ptd->chained_crypto_ops, bufs, nexts,
			   ptd->chunks, ESP_DECRYPT_ERROR_DECRYPTION_FAILED);

  /* Post decryption ronud - adjust packet data start and length and next
     node */

  n_left = from_frame->n_vectors;
  next = nexts;
  pd = pkt_data;
  b = bufs;

  while (n_left)
    {
      const u8 tun_flags = IPSEC_SA_FLAG_IS_TUNNEL |
	IPSEC_SA_FLAG_IS_TUNNEL_V6;

      if (n_left >= 2)
	{
	  void *data = b[1]->data + pd[1].current_data;

	  /* buffer metadata */
	  vlib_prefetch_buffer_header (b[1], LOAD);

	  /* esp_footer_t */
	  CLIB_PREFETCH (data + pd[1].current_length - pd[1].icv_sz - 2,
			 CLIB_CACHE_LINE_BYTES, LOAD);

	  /* packet headers */
	  CLIB_PREFETCH (data - CLIB_CACHE_LINE_BYTES,
			 CLIB_CACHE_LINE_BYTES * 2, LOAD);
	}

      if (next[0] < ESP_DECRYPT_N_NEXT)
	goto trace;

      sa0 = vec_elt_at_index (im->sad, pd->sa_index);

      /*
       * redo the anti-reply check
       * in this frame say we have sequence numbers, s, s+1, s+1, s+1
       * and s and s+1 are in the window. When we did the anti-replay
       * check above we did so against the state of the window (W),
       * after packet s-1. So each of the packets in the sequence will be
       * accepted.
       * This time s will be cheked against Ws-1, s+1 chceked against Ws
       * (i.e. the window state is updated/advnaced)
       * so this time the successive s+! packet will be dropped.
       * This is a consequence of batching the decrypts. If the
       * check-dcrypt-advance process was done for each packet it would
       * be fine. But we batch the decrypts because it's much more efficient
       * to do so in SW and if we offload to HW and the process is async.
       *
       * You're probably thinking, but this means an attacker can send the
       * above sequence and cause VPP to perform decrpyts that will fail,
       * and that's true. But if the attacker can determine s (a valid
       * sequence number in the window) which is non-trivial, it can generate
       * a sequence s, s+1, s+2, s+3, ... s+n and nothing will prevent any
       * implementation, sequential or batching, from decrypting these.
       */
      if (ipsec_sa_anti_replay_check (sa0, pd->seq))
	{
	  b[0]->error = node->errors[ESP_DECRYPT_ERROR_REPLAY];
	  next[0] = ESP_DECRYPT_NEXT_DROP;
	  goto trace;
	}

      ipsec_sa_anti_replay_advance (sa0, pd->seq);

      u8 pad_length = 0, next_header = 0;
      u16 icv_sz = pd->icv_removed ? 0 : pd->icv_sz;

      if (pd->free_buffer_index)
	vlib_buffer_free_one (vm, pd->free_buffer_index);

      if (pd->lb->current_length < sizeof (esp_footer_t) + icv_sz)
	{
	  /* esp footer is either splitted in two buffers or in the before
	   * last buffer */

	  vlib_buffer_t *before_last = b[0], *bp = b[0];
	  while (bp->flags & VLIB_BUFFER_NEXT_PRESENT)
	    {
	      before_last = bp;
	      bp = vlib_get_buffer (vm, bp->next_buffer);
	    }
	  u8 *bt = vlib_buffer_get_tail (before_last);

	  if (pd->lb->current_length == icv_sz)
	    {
	      esp_footer_t *f = (esp_footer_t *) (bt - sizeof (*f));
	      pad_length = f->pad_length;
	      next_header = f->next_header;
	    }
	  else
	    {
	      pad_length = (bt - 1)[0];
	      next_header = ((u8 *) vlib_buffer_get_current (pd->lb))[0];
	    }
	}
      else
	{
	  esp_footer_t *f =
	    (esp_footer_t *) (pd->lb->data + pd->lb->current_data +
			      pd->lb->current_length - sizeof (esp_footer_t) -
			      icv_sz);
	  pad_length = f->pad_length;
	  next_header = f->next_header;
	}

      u16 adv = pd->iv_sz + esp_sz;
      u16 tail = sizeof (esp_footer_t) + pad_length + icv_sz;
      u16 tail_orig = sizeof (esp_footer_t) + pad_length + pd->icv_sz;
      b[0]->flags &= ~VLIB_BUFFER_TOTAL_LENGTH_VALID;

      if ((pd->flags & tun_flags) == 0 && !is_tun)	/* transport mode */
	{
	  u8 udp_sz = (is_ip6 == 0 && pd->flags & IPSEC_SA_FLAG_UDP_ENCAP) ?
	    sizeof (udp_header_t) : 0;
	  u16 ip_hdr_sz = pd->hdr_sz - udp_sz;
	  u8 *old_ip = b[0]->data + pd->current_data - ip_hdr_sz - udp_sz;
	  u8 *ip = old_ip + adv + udp_sz;

	  if (is_ip6 && ip_hdr_sz > 64)
	    memmove (ip, old_ip, ip_hdr_sz);
	  else
	    clib_memcpy_le64 (ip, old_ip, ip_hdr_sz);

	  b[0]->current_data = pd->current_data + adv - ip_hdr_sz;
	  b[0]->current_length = pd->current_length + ip_hdr_sz - adv;
	  esp_remove_tail (vm, b[0], pd->lb, tail);

	  if (is_ip6)
	    {
	      ip6_header_t *ip6 = (ip6_header_t *) ip;
	      u16 len = clib_net_to_host_u16 (ip6->payload_length);
	      len -= adv + tail_orig;
	      ip6->payload_length = clib_host_to_net_u16 (len);
	      ip6->protocol = next_header;
	      next[0] = ESP_DECRYPT_NEXT_IP6_INPUT;
	    }
	  else
	    {
	      ip4_header_t *ip4 = (ip4_header_t *) ip;
	      ip_csum_t sum = ip4->checksum;
	      u16 len = clib_net_to_host_u16 (ip4->length);
	      len = clib_host_to_net_u16 (len - adv - tail_orig - udp_sz);
	      sum = ip_csum_update (sum, ip4->protocol, next_header,
				    ip4_header_t, protocol);
	      sum = ip_csum_update (sum, ip4->length, len,
				    ip4_header_t, length);
	      ip4->checksum = ip_csum_fold (sum);
	      ip4->protocol = next_header;
	      ip4->length = len;
	      next[0] = ESP_DECRYPT_NEXT_IP4_INPUT;
	    }
	}
      else
	{
	  if (PREDICT_TRUE (next_header == IP_PROTOCOL_IP_IN_IP))
	    {
	      next[0] = ESP_DECRYPT_NEXT_IP4_INPUT;
	      b[0]->current_data = pd->current_data + adv;
	      b[0]->current_length = pd->current_length - adv;
	      esp_remove_tail (vm, b[0], pd->lb, tail);
	    }
	  else if (next_header == IP_PROTOCOL_IPV6)
	    {
	      next[0] = ESP_DECRYPT_NEXT_IP6_INPUT;
	      b[0]->current_data = pd->current_data + adv;
	      b[0]->current_length = pd->current_length - adv;
	      esp_remove_tail (vm, b[0], pd->lb, tail);
	    }
	  else
	    {
	      if (is_tun && next_header == IP_PROTOCOL_GRE)
		{
		  gre_header_t *gre;

		  b[0]->current_data = pd->current_data + adv;
		  b[0]->current_length = pd->current_length - adv - tail;

		  gre = vlib_buffer_get_current (b[0]);

		  vlib_buffer_advance (b[0], sizeof (*gre));

		  switch (clib_net_to_host_u16 (gre->protocol))
		    {
		    case GRE_PROTOCOL_teb:
		      vnet_update_l2_len (b[0]);
		      next[0] = ESP_DECRYPT_NEXT_L2_INPUT;
		      break;
		    case GRE_PROTOCOL_ip4:
		      next[0] = ESP_DECRYPT_NEXT_IP4_INPUT;
		      break;
		    case GRE_PROTOCOL_ip6:
		      next[0] = ESP_DECRYPT_NEXT_IP6_INPUT;
		      break;
		    default:
		      b[0]->error =
			node->errors[ESP_DECRYPT_ERROR_UNSUP_PAYLOAD];
		      next[0] = ESP_DECRYPT_NEXT_DROP;
		      break;
		    }
		}
	      else
		{
		  next[0] = ESP_DECRYPT_NEXT_DROP;
		  b[0]->error = node->errors[ESP_DECRYPT_ERROR_UNSUP_PAYLOAD];
		  goto trace;
		}
	    }
	  if (is_tun)
	    {
	      if (ipsec_sa_is_set_IS_PROTECT (sa0))
		{
		  /*
		   * There are two encap possibilities
		   * 1) the tunnel and ths SA are prodiving encap, i.e. it's
		   *   MAC | SA-IP | TUN-IP | ESP | PAYLOAD
		   * implying the SA is in tunnel mode (on a tunnel interface)
		   * 2) only the tunnel provides encap
		   *   MAC | TUN-IP | ESP | PAYLOAD
		   * implying the SA is in transport mode.
		   *
		   * For 2) we need only strip the tunnel encap and we're good.
		   *  since the tunnel and crypto ecnap (int the tun=protect
		   * object) are the same and we verified above that these match
		   * for 1) we need to strip the SA-IP outer headers, to
		   * reveal the tunnel IP and then check that this matches
		   * the configured tunnel.
		   */
		  const ipsec_tun_protect_t *itp;

		  itp = ipsec_tun_protect_get
		    (vnet_buffer (b[0])->ipsec.protect_index);

		  if (PREDICT_TRUE (next_header == IP_PROTOCOL_IP_IN_IP))
		    {
		      const ip4_header_t *ip4;

		      ip4 = vlib_buffer_get_current (b[0]);

		      if (!ip46_address_is_equal_v4 (&itp->itp_tun.src,
						     &ip4->dst_address) ||
			  !ip46_address_is_equal_v4 (&itp->itp_tun.dst,
						     &ip4->src_address))
			{
			  next[0] = ESP_DECRYPT_NEXT_DROP;
			  b[0]->error =
			    node->errors[ESP_DECRYPT_ERROR_TUN_NO_PROTO];
			}
		    }
		  else if (next_header == IP_PROTOCOL_IPV6)
		    {
		      const ip6_header_t *ip6;

		      ip6 = vlib_buffer_get_current (b[0]);

		      if (!ip46_address_is_equal_v6 (&itp->itp_tun.src,
						     &ip6->dst_address) ||
			  !ip46_address_is_equal_v6 (&itp->itp_tun.dst,
						     &ip6->src_address))
			{
			  next[0] = ESP_DECRYPT_NEXT_DROP;
			  b[0]->error =
			    node->errors[ESP_DECRYPT_ERROR_TUN_NO_PROTO];
			}
		    }
		}
	    }
	}

    trace:
      if (PREDICT_FALSE (b[0]->flags & VLIB_BUFFER_IS_TRACED))
	{
	  esp_decrypt_trace_t *tr;
	  tr = vlib_add_trace (vm, node, b[0], sizeof (*tr));
	  sa0 = pool_elt_at_index (im->sad,
				   vnet_buffer (b[0])->ipsec.sad_index);
	  tr->crypto_alg = sa0->crypto_alg;
	  tr->integ_alg = sa0->integ_alg;
	  tr->seq = pd->seq;
	  tr->sa_seq = sa0->last_seq;
	  tr->sa_seq_hi = sa0->seq_hi;
	}

      /* next */
      n_left -= 1;
      next += 1;
      pd += 1;
      b += 1;
    }

  n_left = from_frame->n_vectors;
  vlib_node_increment_counter (vm, node->node_index,
			       ESP_DECRYPT_ERROR_RX_PKTS, n_left);

  vlib_buffer_enqueue_to_next (vm, node, from, nexts, n_left);

  return n_left;
}

VLIB_NODE_FN (esp4_decrypt_node) (vlib_main_t * vm,
				  vlib_node_runtime_t * node,
				  vlib_frame_t * from_frame)
{
  return esp_decrypt_inline (vm, node, from_frame, 0, 0);
}

VLIB_NODE_FN (esp4_decrypt_tun_node) (vlib_main_t * vm,
				      vlib_node_runtime_t * node,
				      vlib_frame_t * from_frame)
{
  return esp_decrypt_inline (vm, node, from_frame, 0, 1);
}

VLIB_NODE_FN (esp6_decrypt_node) (vlib_main_t * vm,
				  vlib_node_runtime_t * node,
				  vlib_frame_t * from_frame)
{
  return esp_decrypt_inline (vm, node, from_frame, 1, 0);
}

VLIB_NODE_FN (esp6_decrypt_tun_node) (vlib_main_t * vm,
				      vlib_node_runtime_t * node,
				      vlib_frame_t * from_frame)
{
  return esp_decrypt_inline (vm, node, from_frame, 1, 1);
}

/* *INDENT-OFF* */
VLIB_REGISTER_NODE (esp4_decrypt_node) = {
  .name = "esp4-decrypt",
  .vector_size = sizeof (u32),
  .format_trace = format_esp_decrypt_trace,
  .type = VLIB_NODE_TYPE_INTERNAL,

  .n_errors = ARRAY_LEN(esp_decrypt_error_strings),
  .error_strings = esp_decrypt_error_strings,

  .n_next_nodes = ESP_DECRYPT_N_NEXT,
  .next_nodes = {
    [ESP_DECRYPT_NEXT_DROP] = "ip4-drop",
    [ESP_DECRYPT_NEXT_IP4_INPUT] = "ip4-input-no-checksum",
    [ESP_DECRYPT_NEXT_IP6_INPUT] = "ip6-input",
    [ESP_DECRYPT_NEXT_L2_INPUT] = "l2-input",
    [ESP_DECRYPT_NEXT_HANDOFF] = "esp4-decrypt-handoff",
  },
};

VLIB_REGISTER_NODE (esp6_decrypt_node) = {
  .name = "esp6-decrypt",
  .vector_size = sizeof (u32),
  .format_trace = format_esp_decrypt_trace,
  .type = VLIB_NODE_TYPE_INTERNAL,

  .n_errors = ARRAY_LEN(esp_decrypt_error_strings),
  .error_strings = esp_decrypt_error_strings,

  .n_next_nodes = ESP_DECRYPT_N_NEXT,
  .next_nodes = {
    [ESP_DECRYPT_NEXT_DROP] = "ip6-drop",
    [ESP_DECRYPT_NEXT_IP4_INPUT] = "ip4-input-no-checksum",
    [ESP_DECRYPT_NEXT_IP6_INPUT] = "ip6-input",
    [ESP_DECRYPT_NEXT_L2_INPUT] = "l2-input",
    [ESP_DECRYPT_NEXT_HANDOFF]=  "esp6-decrypt-handoff",
  },
};

VLIB_REGISTER_NODE (esp4_decrypt_tun_node) = {
  .name = "esp4-decrypt-tun",
  .vector_size = sizeof (u32),
  .format_trace = format_esp_decrypt_trace,
  .type = VLIB_NODE_TYPE_INTERNAL,
  .n_errors = ARRAY_LEN(esp_decrypt_error_strings),
  .error_strings = esp_decrypt_error_strings,
  .n_next_nodes = ESP_DECRYPT_N_NEXT,
  .next_nodes = {
    [ESP_DECRYPT_NEXT_DROP] = "ip4-drop",
    [ESP_DECRYPT_NEXT_IP4_INPUT] = "ip4-input-no-checksum",
    [ESP_DECRYPT_NEXT_IP6_INPUT] = "ip6-input",
    [ESP_DECRYPT_NEXT_L2_INPUT] = "l2-input",
    [ESP_DECRYPT_NEXT_HANDOFF] = "esp4-decrypt-tun-handoff",
  },
};

VLIB_REGISTER_NODE (esp6_decrypt_tun_node) = {
  .name = "esp6-decrypt-tun",
  .vector_size = sizeof (u32),
  .format_trace = format_esp_decrypt_trace,
  .type = VLIB_NODE_TYPE_INTERNAL,
  .n_errors = ARRAY_LEN(esp_decrypt_error_strings),
  .error_strings = esp_decrypt_error_strings,
  .n_next_nodes = ESP_DECRYPT_N_NEXT,
  .next_nodes = {
    [ESP_DECRYPT_NEXT_DROP] = "ip6-drop",
    [ESP_DECRYPT_NEXT_IP4_INPUT] = "ip4-input-no-checksum",
    [ESP_DECRYPT_NEXT_IP6_INPUT] = "ip6-input",
    [ESP_DECRYPT_NEXT_L2_INPUT] = "l2-input",
    [ESP_DECRYPT_NEXT_HANDOFF]=  "esp6-decrypt-tun-handoff",
  },
};
/* *INDENT-ON* */

/*
 * fd.io coding-style-patch-verification: ON
 *
 * Local Variables:
 * eval: (c-set-style "gnu")
 * End:
 */