stack/gatt/gatt_auth.cc

/******************************************************************************
 *
 *  Copyright 1999-2012 Broadcom Corporation
 *
 *  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.
 *
 ******************************************************************************/

/******************************************************************************
 *
 *  this file contains GATT authentication handling functions
 *
 ******************************************************************************/
#include "bt_target.h"
#include "bt_utils.h"

#include <string.h>
#include "bt_common.h"

#include "gatt_api.h"
#include "gatt_int.h"
#include "osi/include/osi.h"
#include "stack/btm/btm_ble_int.h"
#include "stack/btm/btm_ble_int_types.h"
#include "stack/btm/btm_int.h"
#include "stack/btm/btm_sec.h"

using base::StringPrintf;

/*******************************************************************************
 *
 * Function         gatt_sign_data
 *
 * Description      This function sign the data for write command.
 *
 * Returns          true if encrypted, otherwise false.
 *
 ******************************************************************************/
static bool gatt_sign_data(tGATT_CLCB* p_clcb) {
  tGATT_VALUE* p_attr = (tGATT_VALUE*)p_clcb->p_attr_buf;
  uint8_t *p_data = NULL, *p;
  uint16_t payload_size = p_clcb->p_tcb->payload_size;
  bool status = false;
  uint8_t* p_signature;

  /* do not need to mark channel securoty activity for data signing */
  gatt_set_sec_act(p_clcb->p_tcb, GATT_SEC_OK);

  p_data =
      (uint8_t*)osi_malloc(p_attr->len + 3); /* 3 = 2 byte handle + opcode */

  p = p_data;
  UINT8_TO_STREAM(p, GATT_SIGN_CMD_WRITE);
  UINT16_TO_STREAM(p, p_attr->handle);
  ARRAY_TO_STREAM(p, p_attr->value, p_attr->len);

  /* sign data length should be attribulte value length plus 2B handle + 1B op
   * code */
  if ((payload_size - GATT_AUTH_SIGN_LEN - 3) < p_attr->len)
    p_attr->len = payload_size - GATT_AUTH_SIGN_LEN - 3;

  p_signature = p_attr->value + p_attr->len;
  if (BTM_BleDataSignature(
          p_clcb->p_tcb->peer_bda, p_data,
          (uint16_t)(p_attr->len + 3), /* 3 = 2 byte handle + opcode */
          p_signature)) {
    p_attr->len += BTM_BLE_AUTH_SIGN_LEN;
    gatt_set_ch_state(p_clcb->p_tcb, GATT_CH_OPEN);
    gatt_act_write(p_clcb, GATT_SEC_SIGN_DATA);
  } else {
    gatt_end_operation(p_clcb, GATT_INTERNAL_ERROR, NULL);
  }

  osi_free(p_data);

  return status;
}

/*******************************************************************************
 *
 * Function         gatt_verify_signature
 *
 * Description      This function start to verify the sign data when receiving
 *                  the data from peer device.
 *
 * Returns
 *
 ******************************************************************************/
void gatt_verify_signature(tGATT_TCB& tcb, uint16_t cid, BT_HDR* p_buf) {
  uint16_t cmd_len;
  uint8_t op_code;
  uint8_t *p, *p_orig = (uint8_t*)(p_buf + 1) + p_buf->offset;
  uint32_t counter;

  if (p_buf->len < GATT_AUTH_SIGN_LEN + 4) {
    LOG(ERROR) << StringPrintf("%s: Data length %u less than expected %u",
                               __func__, p_buf->len, GATT_AUTH_SIGN_LEN + 4);
    return;
  }
  cmd_len = p_buf->len - GATT_AUTH_SIGN_LEN + 4;
  p = p_orig + cmd_len - 4;
  STREAM_TO_UINT32(counter, p);

  if (!BTM_BleVerifySignature(tcb.peer_bda, p_orig, cmd_len, counter, p)) {
    /* if this is a bad signature, assume from attacker, ignore it  */
    LOG(ERROR) << StringPrintf("Signature Verification Failed, data ignored");
    return;
  }

  STREAM_TO_UINT8(op_code, p_orig);
  gatt_server_handle_client_req(tcb, cid, op_code, (uint16_t)(p_buf->len - 1),
                                p_orig);
}
/*******************************************************************************
 *
 * Function         gatt_sec_check_complete
 *
 * Description      security check complete and proceed to data sending action.
 *
 * Returns          void.
 *
 ******************************************************************************/
void gatt_sec_check_complete(bool sec_check_ok, tGATT_CLCB* p_clcb,
                             uint8_t sec_act) {
  if (p_clcb && p_clcb->p_tcb && p_clcb->p_tcb->pending_enc_clcb.empty()) {
    gatt_set_sec_act(p_clcb->p_tcb, GATT_SEC_NONE);
  }

  if (!sec_check_ok) {
    gatt_end_operation(p_clcb, GATT_AUTH_FAIL, NULL);
  } else if (p_clcb->operation == GATTC_OPTYPE_WRITE) {
    gatt_act_write(p_clcb, sec_act);
  } else if (p_clcb->operation == GATTC_OPTYPE_READ) {
    gatt_act_read(p_clcb, p_clcb->counter);
  }
}
/*******************************************************************************
 *
 * Function         gatt_enc_cmpl_cback
 *
 * Description      link encryption complete callback.
 *
 * Returns
 *
 ******************************************************************************/
void gatt_enc_cmpl_cback(const RawAddress* bd_addr, tBT_TRANSPORT transport,
                         UNUSED_ATTR void* p_ref_data, tBTM_STATUS result) {
  VLOG(1) << StringPrintf("gatt_enc_cmpl_cback");
  tGATT_TCB* p_tcb = gatt_find_tcb_by_addr(*bd_addr, transport);
  if (!p_tcb) {
    LOG(ERROR) << StringPrintf("%s: enc callback for unknown bd_addr",
                               __func__);
    return;
  }

  if (gatt_get_sec_act(p_tcb) == GATT_SEC_ENC_PENDING) return;

  if (p_tcb->pending_enc_clcb.empty()) {
    LOG(ERROR) << StringPrintf("%s: no operation waiting for encrypting",
                               __func__);
    return;
  }

  tGATT_CLCB* p_clcb = p_tcb->pending_enc_clcb.front();
  p_tcb->pending_enc_clcb.pop();

  bool status = false;
  if (result == BTM_SUCCESS) {
    if (gatt_get_sec_act(p_tcb) == GATT_SEC_ENCRYPT_MITM) {
      status = BTM_IsLinkKeyAuthed(*bd_addr, transport);
    } else {
      status = true;
    }
  }

  gatt_sec_check_complete(status, p_clcb, p_tcb->sec_act);

  /* start all other pending operation in queue */
  std::queue<tGATT_CLCB*> new_pending_clcbs;
  while (!p_tcb->pending_enc_clcb.empty()) {
    tGATT_CLCB* p_clcb = p_tcb->pending_enc_clcb.front();
    p_tcb->pending_enc_clcb.pop();
    if (gatt_security_check_start(p_clcb)) new_pending_clcbs.push(p_clcb);
  }
  p_tcb->pending_enc_clcb = new_pending_clcbs;
}

/*******************************************************************************
 *
 * Function         gatt_notify_enc_cmpl
 *
 * Description      link encryption complete notification for all encryption
 *                  process initiated outside GATT.
 *
 * Returns
 *
 ******************************************************************************/
void gatt_notify_enc_cmpl(const RawAddress& bd_addr) {
  tGATT_TCB* p_tcb = gatt_find_tcb_by_addr(bd_addr, BT_TRANSPORT_LE);
  if (!p_tcb) {
    VLOG(1) << StringPrintf(
        "notify GATT for encryption completion of unknown device");
    return;
  }

  for (uint8_t i = 0; i < GATT_MAX_APPS; i++) {
    if (gatt_cb.cl_rcb[i].in_use && gatt_cb.cl_rcb[i].app_cb.p_enc_cmpl_cb) {
      (*gatt_cb.cl_rcb[i].app_cb.p_enc_cmpl_cb)(gatt_cb.cl_rcb[i].gatt_if,
                                                bd_addr);
    }
  }

  if (gatt_get_sec_act(p_tcb) == GATT_SEC_ENC_PENDING) {
    gatt_set_sec_act(p_tcb, GATT_SEC_NONE);

    std::queue<tGATT_CLCB*> new_pending_clcbs;
    while (!p_tcb->pending_enc_clcb.empty()) {
      tGATT_CLCB* p_clcb = p_tcb->pending_enc_clcb.front();
      p_tcb->pending_enc_clcb.pop();
      if (gatt_security_check_start(p_clcb)) new_pending_clcbs.push(p_clcb);
    }
    p_tcb->pending_enc_clcb = new_pending_clcbs;
  }
}
/*******************************************************************************
 *
 * Function         gatt_set_sec_act
 *
 * Description      This function set the sec_act in clcb
 *
 * Returns          none
 *
 ******************************************************************************/
void gatt_set_sec_act(tGATT_TCB* p_tcb, tGATT_SEC_ACTION sec_act) {
  if (p_tcb) {
    p_tcb->sec_act = sec_act;
  }
}
/*******************************************************************************
 *
 * Function         gatt_get_sec_act
 *
 * Description      This function get the sec_act in clcb
 *
 * Returns          none
 *
 ******************************************************************************/
tGATT_SEC_ACTION gatt_get_sec_act(tGATT_TCB* p_tcb) {
  tGATT_SEC_ACTION sec_act = GATT_SEC_NONE;
  if (p_tcb) {
    sec_act = p_tcb->sec_act;
  }
  return sec_act;
}
/**
 * This routine determine the security action based on auth_request and current
 * link status. Returns tGATT_SEC_ACTION (security action)
 */
tGATT_SEC_ACTION gatt_determine_sec_act(tGATT_CLCB* p_clcb) {
  tGATT_SEC_ACTION act = GATT_SEC_OK;
  tGATT_TCB* p_tcb = p_clcb->p_tcb;
  tGATT_AUTH_REQ auth_req = p_clcb->auth_req;
  bool is_link_encrypted = false;
  bool is_link_key_known = false;
  bool is_key_mitm = false;
  uint8_t key_type;
  tBTM_BLE_SEC_REQ_ACT sec_act = BTM_BLE_SEC_REQ_ACT_NONE;

  if (auth_req == GATT_AUTH_REQ_NONE) return act;

  btm_ble_link_sec_check(p_tcb->peer_bda, auth_req, &sec_act);

  /* if a encryption is pending, need to wait */
  if (sec_act == BTM_BLE_SEC_REQ_ACT_DISCARD && auth_req != GATT_AUTH_REQ_NONE)
    return GATT_SEC_ENC_PENDING;

  is_link_key_known =
      BTM_IsLinkKeyKnown(p_tcb->peer_bda, p_clcb->p_tcb->transport);
  is_link_encrypted =
      BTM_IsEncrypted(p_tcb->peer_bda, p_clcb->p_tcb->transport);
  is_key_mitm = BTM_IsLinkKeyAuthed(p_tcb->peer_bda, p_clcb->p_tcb->transport);

  /* first check link key upgrade required or not */
  switch (auth_req) {
    case GATT_AUTH_REQ_MITM:
    case GATT_AUTH_REQ_SIGNED_MITM:
      if (!is_key_mitm) act = GATT_SEC_ENCRYPT_MITM;
      break;

    case GATT_AUTH_REQ_NO_MITM:
    case GATT_AUTH_REQ_SIGNED_NO_MITM:
      if (!is_link_key_known) act = GATT_SEC_ENCRYPT_NO_MITM;
      break;
    default:
      break;
  }

  /* now check link needs to be encrypted or not if the link key upgrade is not
   * required */
  if (act == GATT_SEC_OK) {
    if (p_tcb->transport == BT_TRANSPORT_LE &&
        (p_clcb->operation == GATTC_OPTYPE_WRITE) &&
        (p_clcb->op_subtype == GATT_WRITE_NO_RSP)) {
      /* this is a write command request
         check data signing required or not */
      if (!is_link_encrypted) {
        btm_ble_get_enc_key_type(p_tcb->peer_bda, &key_type);

        if ((key_type & BTM_LE_KEY_LCSRK) &&
            ((auth_req == GATT_AUTH_REQ_SIGNED_NO_MITM) ||
             (auth_req == GATT_AUTH_REQ_SIGNED_MITM))) {
          act = GATT_SEC_SIGN_DATA;
        } else {
          act = GATT_SEC_ENCRYPT;
        }
      }
    } else {
      if (!is_link_encrypted) {
        act = GATT_SEC_ENCRYPT;
      }
    }
  }

  return act;
}

/*******************************************************************************
 *
 * Function         gatt_get_link_encrypt_status
 *
 * Description      This routine get the encryption status of the specified link
 *
 *
 * Returns          tGATT_STATUS link encryption status
 *
 ******************************************************************************/
tGATT_STATUS gatt_get_link_encrypt_status(tGATT_TCB& tcb) {
  tGATT_STATUS encrypt_status = GATT_NOT_ENCRYPTED;

  bool encrypted = BTM_IsEncrypted(tcb.peer_bda, tcb.transport);
  bool link_key_known = BTM_IsLinkKeyKnown(tcb.peer_bda, tcb.transport);
  bool link_key_authed = BTM_IsLinkKeyAuthed(tcb.peer_bda, tcb.transport);

  if (encrypted && link_key_known) {
    encrypt_status = GATT_ENCRYPED_NO_MITM;
    if (link_key_authed) {
      encrypt_status = GATT_ENCRYPED_MITM;
    }
  }

  VLOG(1) << StringPrintf("gatt_get_link_encrypt_status status=0x%x",
                          encrypt_status);
  return encrypt_status;
}

/*******************************************************************************
 *
 * Function         gatt_convert_sec_action
 *
 * Description      Convert GATT security action enum into equivalent
 *                  BTM BLE security action enum
 *
 * Returns          bool    true - conversation is successful
 *
 ******************************************************************************/
static bool gatt_convert_sec_action(tGATT_SEC_ACTION gatt_sec_act,
                                    tBTM_BLE_SEC_ACT* p_btm_sec_act) {
  bool status = true;
  switch (gatt_sec_act) {
    case GATT_SEC_ENCRYPT:
      *p_btm_sec_act = BTM_BLE_SEC_ENCRYPT;
      break;
    case GATT_SEC_ENCRYPT_NO_MITM:
      *p_btm_sec_act = BTM_BLE_SEC_ENCRYPT_NO_MITM;
      break;
    case GATT_SEC_ENCRYPT_MITM:
      *p_btm_sec_act = BTM_BLE_SEC_ENCRYPT_MITM;
      break;
    default:
      status = false;
      break;
  }

  return status;
}

/** check link security, return true if p_clcb should be added back to queue */
bool gatt_security_check_start(tGATT_CLCB* p_clcb) {
  tGATT_TCB* p_tcb = p_clcb->p_tcb;
  tGATT_SEC_ACTION sec_act_old = gatt_get_sec_act(p_tcb);

  tGATT_SEC_ACTION gatt_sec_act = gatt_determine_sec_act(p_clcb);

  if (sec_act_old == GATT_SEC_NONE) gatt_set_sec_act(p_tcb, gatt_sec_act);

  switch (gatt_sec_act) {
    case GATT_SEC_SIGN_DATA:
      VLOG(1) << StringPrintf("%s: Do data signing", __func__);
      gatt_sign_data(p_clcb);
      break;
    case GATT_SEC_ENCRYPT:
    case GATT_SEC_ENCRYPT_NO_MITM:
    case GATT_SEC_ENCRYPT_MITM:
      if (sec_act_old < GATT_SEC_ENCRYPT) {
        VLOG(1) << StringPrintf("%s: Encrypt now or key upgreade first",
                                __func__);
        tBTM_BLE_SEC_ACT btm_ble_sec_act;
        gatt_convert_sec_action(gatt_sec_act, &btm_ble_sec_act);
        tBTM_STATUS btm_status =
            BTM_SetEncryption(p_tcb->peer_bda, p_tcb->transport,
                              gatt_enc_cmpl_cback, NULL, btm_ble_sec_act);
        if ((btm_status != BTM_SUCCESS) && (btm_status != BTM_CMD_STARTED)) {
          LOG(ERROR) << StringPrintf(
              "%s BTM_SetEncryption failed btm_status=%d", __func__,
              btm_status);
          gatt_set_sec_act(p_tcb, GATT_SEC_NONE);
          gatt_set_ch_state(p_tcb, GATT_CH_OPEN);

          gatt_end_operation(p_clcb, GATT_INSUF_ENCRYPTION, NULL);
          return false;
        }
      }
      return true;
    case GATT_SEC_ENC_PENDING:
      /* wait for link encrypotion to finish */
      return true;
    default:
      gatt_sec_check_complete(true, p_clcb, gatt_sec_act);
      break;
  }

  return false;
}