/*
 * 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/ipsec/ipsec.h>
#include <vnet/ipsec/esp.h>

#define ESP_WINDOW_SIZE 64

#define foreach_esp_decrypt_next                \
_(DROP, "error-drop")                           \
_(IP4_INPUT, "ip4-input")                       \
_(IP6_INPUT, "ip6-input")

#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")                    \
 _(NO_BUFFER, "No buffer (packed dropped)")         \
 _(DECRYPTION_FAILED, "ESP decryption failed")      \
 _(INTEG_ERROR, "Integrity check failed")           \
 _(REPLAY, "SA replayed packet")


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 {
  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",
              format_ipsec_crypto_alg, t->crypto_alg,
              format_ipsec_integ_alg, t->integ_alg);
  return s;
}

always_inline void
esp_decrypt_aes_cbc(ipsec_crypto_alg_t alg,
                    u8 * in,
                    u8 * out,
                    size_t in_len,
                    u8 * key,
                    u8 * iv)
{
  esp_main_t * em = &esp_main;
  EVP_CIPHER_CTX * ctx = &(em->decrypt_ctx);
  const EVP_CIPHER * cipher = NULL;
  int out_len;

  ASSERT(alg < IPSEC_CRYPTO_N_ALG);

  if (PREDICT_FALSE(em->esp_crypto_algs[alg].type == 0))
    return;

  if (PREDICT_FALSE(alg != em->last_decrytp_alg)) {
    cipher = em->esp_crypto_algs[alg].type;
    em->last_decrytp_alg = alg;
  }

  EVP_DecryptInit_ex(ctx, cipher, NULL, key, iv);

  EVP_DecryptUpdate(ctx, out, &out_len, in, in_len);
  EVP_DecryptFinal_ex(ctx, out + out_len, &out_len);
}

always_inline int
esp_replay_check (ipsec_sa_t * sa, u32 seq)
{
  u32 diff;

  if (PREDICT_TRUE(seq > sa->last_seq))
    return 0;

  diff = sa->last_seq - seq;

  if (ESP_WINDOW_SIZE > diff)
    return (sa->replay_window & (1ULL << diff)) ? 1 : 0;
  else
    return 1;

  return 0;
}

always_inline int
esp_replay_check_esn (ipsec_sa_t * sa, u32 seq)
{
  u32 tl = sa->last_seq;
  u32 th = sa->last_seq_hi;
  u32 diff = tl - seq;

  if (PREDICT_TRUE(tl >= (ESP_WINDOW_SIZE - 1)))
    {
      if (seq >= (tl - ESP_WINDOW_SIZE + 1))
        {
          sa->seq_hi = th;
          if (seq <= tl)
            return (sa->replay_window & (1ULL << diff)) ? 1 : 0;
          else
            return 0;
        }
      else
        {
          sa->seq_hi = th + 1;
          return 0;
        }
    }
  else
    {
      if (seq >= (tl - ESP_WINDOW_SIZE + 1))
        {
          sa->seq_hi = th - 1;
          return (sa->replay_window & (1ULL << diff)) ? 1 : 0;
        }
      else
        {
          sa->seq_hi = th;
          if (seq <= tl)
            return (sa->replay_window & (1ULL << diff)) ? 1 : 0;
          else
            return 0;
        }
    }

  return 0;
}

always_inline void
esp_replay_advance (ipsec_sa_t * sa, u32 seq)
{
  u32 pos;

  if (seq > sa->last_seq)
    {
      pos = seq - sa->last_seq;
      if (pos < ESP_WINDOW_SIZE)
        sa->replay_window = ((sa->replay_window) << pos) | 1;
      else
        sa->replay_window = 1;
      sa->last_seq = seq;
    }
  else
    {
      pos = sa->last_seq - seq;
      sa->replay_window |= (1ULL << pos);
    }
}

always_inline void
esp_replay_advance_esn (ipsec_sa_t * sa, u32 seq)
{
  int wrap = sa->seq_hi - sa->last_seq_hi;
  u32 pos;

  if (wrap == 0 && seq > sa->last_seq)
    {
      pos = seq - sa->last_seq;
      if (pos < ESP_WINDOW_SIZE)
        sa->replay_window = ((sa->replay_window) << pos) | 1;
      else
        sa->replay_window = 1;
      sa->last_seq = seq;
    }
  else if (wrap > 0)
    {
      pos = ~seq + sa->last_seq + 1;
      if (pos < ESP_WINDOW_SIZE)
        sa->replay_window = ((sa->replay_window) << pos) | 1;
      else
        sa->replay_window = 1;
      sa->last_seq = seq;
      sa->last_seq_hi = sa->seq_hi;
    }
  else if (wrap < 0)
    {
      pos = ~seq + sa->last_seq + 1;
      sa->replay_window |= (1ULL << pos);
    }
  else
    {
      pos = sa->last_seq - seq;
      sa->replay_window |= (1ULL << pos);
    }
}

static uword
esp_decrypt_node_fn (vlib_main_t * vm,
		     vlib_node_runtime_t * node,
		     vlib_frame_t * from_frame)
{
  u32 n_left_from, *from, next_index, *to_next;
  ipsec_main_t *im = &ipsec_main;
  esp_main_t *em = &esp_main;
  u32 * recycle = 0;
  from = vlib_frame_vector_args (from_frame);
  n_left_from = from_frame->n_vectors;

  ipsec_alloc_empty_buffers(vm, im);

  if (PREDICT_FALSE(vec_len (im->empty_buffers) < n_left_from)){
    vlib_node_increment_counter (vm, esp_decrypt_node.index,
                                 ESP_DECRYPT_ERROR_NO_BUFFER, n_left_from);
    goto free_buffers_and_exit;
  }

  next_index = node->cached_next_index;

  while (n_left_from > 0)
    {
      u32 n_left_to_next;

      vlib_get_next_frame (vm, node, next_index, to_next, n_left_to_next);

      while (n_left_from > 0 && n_left_to_next > 0)
        {
          u32 i_bi0, o_bi0 = (u32) ~0, next0;
          vlib_buffer_t * i_b0;
          vlib_buffer_t * o_b0 = 0;
          esp_header_t * esp0;
          ipsec_sa_t * sa0;
          u32 sa_index0 = ~0;
          u32 seq;

          i_bi0 = from[0];
          from += 1;
          n_left_from -= 1;
          n_left_to_next -= 1;

          next0 = ESP_DECRYPT_NEXT_DROP;

          i_b0 = vlib_get_buffer (vm, i_bi0);
          esp0 = vlib_buffer_get_current (i_b0);

          sa_index0 = vnet_buffer(i_b0)->output_features.ipsec_sad_index;
          sa0 = pool_elt_at_index (im->sad, sa_index0);

          seq = clib_host_to_net_u32(esp0->seq);

          /* anti-replay check */
          if (sa0->use_anti_replay)
            {
              int rv = 0;

              if (PREDICT_TRUE(sa0->use_esn))
                rv = esp_replay_check_esn(sa0, seq);
              else
                rv = esp_replay_check(sa0, seq);

              if (PREDICT_FALSE(rv))
                {
                  clib_warning("anti-replay SPI %u seq %u", sa0->spi, seq);
                  vlib_node_increment_counter (vm, esp_decrypt_node.index,
                                               ESP_DECRYPT_ERROR_REPLAY, 1);
                  o_bi0 = i_bi0;
                  goto trace;
                }
            }

          if (PREDICT_TRUE(sa0->integ_alg != IPSEC_INTEG_ALG_NONE))
            {
              u8 sig[64];
              int icv_size = em->esp_integ_algs[sa0->integ_alg].trunc_size;
              memset(sig, 0, sizeof(sig));
              u8 * icv = vlib_buffer_get_current (i_b0) + i_b0->current_length - icv_size;
              i_b0->current_length -= icv_size;

              hmac_calc(sa0->integ_alg, sa0->integ_key, sa0->integ_key_len,
                        (u8 *) esp0, i_b0->current_length, sig, sa0->use_esn,
                        sa0->seq_hi);

              if (PREDICT_FALSE(memcmp(icv, sig, icv_size)))
                {
                  vlib_node_increment_counter (vm, esp_decrypt_node.index,
                                               ESP_DECRYPT_ERROR_INTEG_ERROR, 1);
                  o_bi0 = i_bi0;
                  goto trace;
                }
            }

          if (PREDICT_TRUE(sa0->use_anti_replay))
            {
              if (PREDICT_TRUE(sa0->use_esn))
                esp_replay_advance_esn(sa0, seq);
              else
                esp_replay_advance(sa0, seq);
             }

          /* grab free buffer */
          uword last_empty_buffer = vec_len (im->empty_buffers) - 1;
          o_bi0 = im->empty_buffers[last_empty_buffer];
          o_b0 = vlib_get_buffer (vm, o_bi0);
          vlib_prefetch_buffer_with_index (vm, im->empty_buffers[last_empty_buffer-1], STORE);
          _vec_len (im->empty_buffers) = last_empty_buffer;

          /* add old buffer to the recycle list */
          vec_add1(recycle, i_bi0);

          if (sa0->crypto_alg >= IPSEC_CRYPTO_ALG_AES_CBC_128 &&
              sa0->crypto_alg <= IPSEC_CRYPTO_ALG_AES_CBC_256) {
            const int BLOCK_SIZE = 16;
            const int IV_SIZE = 16;
            esp_footer_t * f0;

            int blocks = (i_b0->current_length - sizeof (esp_header_t) - IV_SIZE) / BLOCK_SIZE;

            o_b0->current_data = sizeof(ethernet_header_t);

            esp_decrypt_aes_cbc(sa0->crypto_alg,
                                esp0->data + IV_SIZE,
                                (u8 *) vlib_buffer_get_current (o_b0),
                                BLOCK_SIZE * blocks,
                                sa0->crypto_key,
                                esp0->data);

            o_b0->current_length = (blocks * 16) - 2;
            o_b0->flags = VLIB_BUFFER_TOTAL_LENGTH_VALID;
            f0 = (esp_footer_t *) ((u8 *) vlib_buffer_get_current (o_b0) + o_b0->current_length);
            o_b0->current_length -= f0->pad_length;
            if (PREDICT_TRUE(f0->next_header == IP_PROTOCOL_IP_IN_IP))
              next0 = ESP_DECRYPT_NEXT_IP4_INPUT;
            else if (f0->next_header == IP_PROTOCOL_IPV6)
              next0 = ESP_DECRYPT_NEXT_IP6_INPUT;
            else
              {
                clib_warning("next header: 0x%x", f0->next_header);
                vlib_node_increment_counter (vm, esp_decrypt_node.index,
                                             ESP_DECRYPT_ERROR_DECRYPTION_FAILED,
                                             1);
                o_b0 = 0;
                goto trace;
              }

            to_next[0] = o_bi0;
            to_next += 1;

            vnet_buffer (o_b0)->sw_if_index[VLIB_TX] = (u32)~0;
          }

trace:
          if (PREDICT_FALSE(i_b0->flags & VLIB_BUFFER_IS_TRACED)) {
            if (o_b0) {
              o_b0->flags |= VLIB_BUFFER_IS_TRACED;
              o_b0->trace_index = i_b0->trace_index;
            }
            esp_decrypt_trace_t *tr = vlib_add_trace (vm, node, o_b0, sizeof (*tr));
            tr->crypto_alg = sa0->crypto_alg;
            tr->integ_alg = sa0->integ_alg;
          }

	  vlib_validate_buffer_enqueue_x1 (vm, node, next_index, to_next,
                                           n_left_to_next, o_bi0, next0);
        }
      vlib_put_next_frame (vm, node, next_index, n_left_to_next);
    }
  vlib_node_increment_counter (vm, esp_decrypt_node.index,
                               ESP_DECRYPT_ERROR_RX_PKTS,
                               from_frame->n_vectors);

free_buffers_and_exit:
  vlib_buffer_free (vm, recycle, vec_len(recycle));
  vec_free(recycle);
  return from_frame->n_vectors;
}


VLIB_REGISTER_NODE (esp_decrypt_node) = {
  .function = esp_decrypt_node_fn,
  .name = "esp-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 = {
#define _(s,n) [ESP_DECRYPT_NEXT_##s] = n,
    foreach_esp_decrypt_next
#undef _
  },
};