curl.c

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/*
 * Asterisk -- An open source telephony toolkit.
 *
 * Copyright (C) 2020, Sangoma Technologies Corporation
 *
 * Ben Ford <[email protected]>
 *
 * See http://www.asterisk.org for more information about
 * the Asterisk project. Please do not directly contact
 * any of the maintainers of this project for assistance;
 * the project provides a web site, mailing lists and IRC
 * channels for your use.
 *
 * This program is free software, distributed under the terms of
 * the GNU General Public License Version 2. See the LICENSE file
 * at the top of the source tree.
 */

#include "asterisk.h"

#include "asterisk/utils.h"
#include "asterisk/logger.h"
#include "curl.h"
#include "general.h"
#include "stir_shaken.h"

#include <curl/curl.h>
#include <sys/stat.h>

/* Used to check CURL headers */
#define MAX_HEADER_LENGTH 1023

/* Used for CURL requests */
#define GLOBAL_USERAGENT "asterisk-libcurl-agent/1.0"

/* CURL callback data to avoid storing useless info in AstDB */
struct curl_cb_data {
   char *cache_control;
   char *expires;
};

struct curl_cb_data *curl_cb_data_create(void)
{
   struct curl_cb_data *data;

   data = ast_calloc(1, sizeof(*data));

   return data;
}

void curl_cb_data_free(struct curl_cb_data *data)
{
   if (!data) {
      return;
   }

   ast_free(data->cache_control);
   ast_free(data->expires);

   ast_free(data);
}

char *curl_cb_data_get_cache_control(const struct curl_cb_data *data)
{
   if (!data) {
      return NULL;
   }

   return data->cache_control;
}

char *curl_cb_data_get_expires(const struct curl_cb_data *data)
{
   if (!data) {
      return NULL;
   }

   return data->expires;
}

/*!
 * \brief Called when a CURL request completes
 *
 * \param data The curl_cb_data structure to store expiration info
 */
static size_t curl_header_callback(char *buffer, size_t size, size_t nitems, void *data)
{
   struct curl_cb_data *cb_data = data;
   size_t realsize;
   char *header;
   char *value;

   realsize = size * nitems;

   if (realsize > MAX_HEADER_LENGTH) {
      ast_log(LOG_WARNING, "CURL header length is too large (size: '%zu' | max: '%d')\n",
         realsize, MAX_HEADER_LENGTH);
      return 0;
   }

   header = ast_alloca(realsize + 1);
   memcpy(header, buffer, realsize);
   header[realsize] = '\0';
   value = strchr(header, ':');
   if (!value) {
      return realsize;
   }
   *value++ = '\0';
   value = ast_trim_blanks(ast_skip_blanks(value));

   if (!strcasecmp(header, "Cache-Control")) {
      cb_data->cache_control = ast_strdup(value);
   } else if (!strcasecmp(header, "Expires")) {
      cb_data->expires = ast_strdup(value);
   }

   return realsize;
}

/*!
 * \brief Prepare a CURL instance to use
 *
 * \param data The CURL callback data
 *
 * \retval NULL on failure
 * \retval CURL instance on success
 */
static CURL *get_curl_instance(struct curl_cb_data *data)
{
   CURL *curl;
   struct stir_shaken_general *cfg;
   unsigned int curl_timeout;

   cfg = stir_shaken_general_get();
   curl_timeout = ast_stir_shaken_curl_timeout(cfg);
   ao2_cleanup(cfg);

   curl = curl_easy_init();
   if (!curl) {
      return NULL;
   }

   curl_easy_setopt(curl, CURLOPT_NOSIGNAL, 1);
   curl_easy_setopt(curl, CURLOPT_TIMEOUT, curl_timeout);
   curl_easy_setopt(curl, CURLOPT_USERAGENT, GLOBAL_USERAGENT);
   curl_easy_setopt(curl, CURLOPT_FOLLOWLOCATION, 1);
   curl_easy_setopt(curl, CURLOPT_HEADERFUNCTION, curl_header_callback);
   curl_easy_setopt(curl, CURLOPT_HEADERDATA, data);

   return curl;
}

/*!
 * \brief Create a temporary file located at path
 *
 * \note This function assumes path does not end with a '/'
 *
 * \param path The directory path to create the file in
 * \param filename Function allocates memory and stores full filename (including path) here
 *
 * \retval -1 on failure
 * \retval file descriptor on success
 */
static int create_temp_file(const char *path, char **filename)
{
   const char *template_name = "certXXXXXX";
   int fd;

   if (ast_asprintf(filename, "%s/%s", path, template_name) < 0) {
      ast_log(LOG_ERROR, "Failed to set up temporary file path for CURL\n");
      return -1;
   }

   ast_mkdir(path, 0644);

   if ((fd = mkstemp(*filename)) < 0) {
      ast_log(LOG_NOTICE, "Failed to create temporary file for CURL\n");
      ast_free(*filename);
      return -1;
   }

   return fd;
}

char *curl_public_key(const char *public_cert_url, const char *path, struct curl_cb_data *data)
{
   FILE *public_key_file;
   RAII_VAR(char *, tmp_filename, NULL, ast_free);
   char *filename;
   char *serial;
   int fd;
   long http_code;
   CURL *curl;
   char curl_errbuf[CURL_ERROR_SIZE + 1];

   curl_errbuf[CURL_ERROR_SIZE] = '\0';

   /* For now, it's fine to pass in path as is - it shouldn't end with a '/'. However,
    * if we decide to change how certificates are stored in the future (configurable paths),
    * then we will need to check to see if path ends with '/', copy everything up to the '/',
    * and use this new variable for create_temp_file as well as for ast_asprintf below.
    */
   fd = create_temp_file(path, &tmp_filename);
   if (fd == -1) {
      ast_log(LOG_ERROR, "Failed to get temporary file descriptor for CURL\n");
      return NULL;
   }

   public_key_file = fdopen(fd, "wb");
   if (!public_key_file) {
      ast_log(LOG_ERROR, "Failed to open file '%s' to write public key from '%s': %s (%d)\n",
         tmp_filename, public_cert_url, strerror(errno), errno);
      close(fd);
      remove(tmp_filename);
      return NULL;
   }

   curl = get_curl_instance(data);
   if (!curl) {
      ast_log(LOG_ERROR, "Failed to set up CURL isntance for '%s'\n", public_cert_url);
      fclose(public_key_file);
      remove(tmp_filename);
      return NULL;
   }

   curl_easy_setopt(curl, CURLOPT_URL, public_cert_url);
   curl_easy_setopt(curl, CURLOPT_WRITEDATA, public_key_file);
   curl_easy_setopt(curl, CURLOPT_ERRORBUFFER, curl_errbuf);

   if (curl_easy_perform(curl)) {
      ast_log(LOG_ERROR, "%s\n", curl_errbuf);
      curl_easy_cleanup(curl);
      fclose(public_key_file);
      remove(tmp_filename);
      return NULL;
   }

   curl_easy_getinfo(curl, CURLINFO_RESPONSE_CODE, &http_code);

   curl_easy_cleanup(curl);
   fclose(public_key_file);

   if (http_code / 100 != 2) {
      ast_log(LOG_ERROR, "Failed to retrieve URL '%s': code %ld\n", public_cert_url, http_code);
      remove(tmp_filename);
      return NULL;
   }

   serial = stir_shaken_get_serial_number_x509(tmp_filename);
   if (!serial) {
      ast_log(LOG_ERROR, "Failed to get serial from cert %s\n", tmp_filename);
      remove(tmp_filename);
      return NULL;
   }

   if (ast_asprintf(&filename, "%s/%s.pem", path, serial) < 0) {
      ast_log(LOG_ERROR, "Failed to allocate memory for new filename for temporary "
         "file %s after CURL\n", tmp_filename);
      ast_free(serial);
      remove(tmp_filename);
      return NULL;
   }

   ast_free(serial);

   if (rename(tmp_filename, filename)) {
      ast_log(LOG_ERROR, "Failed to rename temporary file %s to %s after CURL\n", tmp_filename, filename);
      ast_free(filename);
      remove(tmp_filename);
      return NULL;
   }

   return filename;
}