pbx_functions.c

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/*
 * Asterisk -- An open source telephony toolkit.
 *
 * Copyright (C) 2015, CFWare, LLC
 *
 * Corey Farrell <[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.
 */

/*! \file
 *
 * \brief Custom function management routines.
 *
 * \author Corey Farrell <[email protected]>
 */

/*** MODULEINFO
   <support_level>core</support_level>
 ***/

#include "asterisk.h"

#include "asterisk/_private.h"
#include "asterisk/cli.h"
#include "asterisk/linkedlists.h"
#include "asterisk/module.h"
#include "asterisk/pbx.h"
#include "asterisk/term.h"
#include "asterisk/threadstorage.h"
#include "asterisk/xmldoc.h"
#include "pbx_private.h"

/*!
 * \brief A thread local indicating whether the current thread can run
 * 'dangerous' dialplan functions.
 */
AST_THREADSTORAGE(thread_inhibit_escalations_tl);

/*!
 * \brief Set to true (non-zero) to globally allow all dangerous dialplan
 * functions to run.
 */
static int live_dangerously;

/*!
 * \brief Registered functions container.
 *
 * It is sorted by function name.
 */
static AST_RWLIST_HEAD_STATIC(acf_root, ast_custom_function);

static char *handle_show_functions(struct ast_cli_entry *e, int cmd, struct ast_cli_args *a)
{
   struct ast_custom_function *acf;
   int count_acf = 0;
   int like = 0;

   switch (cmd) {
   case CLI_INIT:
      e->command = "core show functions [like]";
      e->usage =
         "Usage: core show functions [like <text>]\n"
         "       List builtin functions, optionally only those matching a given string\n";
      return NULL;
   case CLI_GENERATE:
      return NULL;
   }

   if (a->argc == 5 && (!strcmp(a->argv[3], "like")) ) {
      like = 1;
   } else if (a->argc != 3) {
      return CLI_SHOWUSAGE;
   }

   ast_cli(a->fd, "%s Custom Functions:\n"
      "--------------------------------------------------------------------------------\n",
      like ? "Matching" : "Installed");

   AST_RWLIST_RDLOCK(&acf_root);
   AST_RWLIST_TRAVERSE(&acf_root, acf, acflist) {
      if (!like || strstr(acf->name, a->argv[4])) {
         count_acf++;
         ast_cli(a->fd, "%-20.20s  %-35.35s  %s\n",
            S_OR(acf->name, ""),
            S_OR(acf->syntax, ""),
            S_OR(acf->synopsis, ""));
      }
   }
   AST_RWLIST_UNLOCK(&acf_root);

   ast_cli(a->fd, "%d %scustom functions installed.\n", count_acf, like ? "matching " : "");

   return CLI_SUCCESS;
}

static char *complete_functions(const char *word, int pos, int state)
{
   struct ast_custom_function *cur;
   char *ret = NULL;
   int which = 0;
   int wordlen;
   int cmp;

   if (pos != 3) {
      return NULL;
   }

   wordlen = strlen(word);
   AST_RWLIST_RDLOCK(&acf_root);
   AST_RWLIST_TRAVERSE(&acf_root, cur, acflist) {
      /*
       * Do a case-insensitive search for convenience in this
       * 'complete' function.
       *
       * We must search the entire container because the functions are
       * sorted and normally found case sensitively.
       */
      cmp = strncasecmp(word, cur->name, wordlen);
      if (!cmp) {
         /* Found match. */
         if (++which <= state) {
            /* Not enough matches. */
            continue;
         }
         ret = ast_strdup(cur->name);
         break;
      }
   }
   AST_RWLIST_UNLOCK(&acf_root);

   return ret;
}

static char *handle_show_function(struct ast_cli_entry *e, int cmd, struct ast_cli_args *a)
{
   struct ast_custom_function *acf;
   /* Maximum number of characters added by terminal coloring is 22 */
   char infotitle[64 + AST_MAX_APP + 22], syntitle[40], destitle[40], argtitle[40], seealsotitle[40];
   char info[64 + AST_MAX_APP], *synopsis = NULL, *description = NULL, *seealso = NULL;
   char stxtitle[40], *syntax = NULL, *arguments = NULL;
   int syntax_size, description_size, synopsis_size, arguments_size, seealso_size;

   switch (cmd) {
   case CLI_INIT:
      e->command = "core show function";
      e->usage =
         "Usage: core show function <function>\n"
         "       Describe a particular dialplan function.\n";
      return NULL;
   case CLI_GENERATE:
      return complete_functions(a->word, a->pos, a->n);
   }

   if (a->argc != 4) {
      return CLI_SHOWUSAGE;
   }

   if (!(acf = ast_custom_function_find(a->argv[3]))) {
      ast_cli(a->fd, "No function by that name registered.\n");

      return CLI_FAILURE;
   }

   syntax_size = strlen(S_OR(acf->syntax, "Not Available")) + AST_TERM_MAX_ESCAPE_CHARS;
   syntax = ast_malloc(syntax_size);
   if (!syntax) {
      ast_cli(a->fd, "Memory allocation failure!\n");

      return CLI_FAILURE;
   }

   snprintf(info, sizeof(info), "\n  -= Info about function '%s' =- \n\n", acf->name);
   term_color(infotitle, info, COLOR_MAGENTA, 0, sizeof(infotitle));
   term_color(syntitle, "[Synopsis]\n", COLOR_MAGENTA, 0, 40);
   term_color(destitle, "[Description]\n", COLOR_MAGENTA, 0, 40);
   term_color(stxtitle, "[Syntax]\n", COLOR_MAGENTA, 0, 40);
   term_color(argtitle, "[Arguments]\n", COLOR_MAGENTA, 0, 40);
   term_color(seealsotitle, "[See Also]\n", COLOR_MAGENTA, 0, 40);
   term_color(syntax, S_OR(acf->syntax, "Not available"), COLOR_CYAN, 0, syntax_size);
#ifdef AST_XML_DOCS
   if (acf->docsrc == AST_XML_DOC) {
      arguments = ast_xmldoc_printable(S_OR(acf->arguments, "Not available"), 1);
      synopsis = ast_xmldoc_printable(S_OR(acf->synopsis, "Not available"), 1);
      description = ast_xmldoc_printable(S_OR(acf->desc, "Not available"), 1);
      seealso = ast_xmldoc_printable(S_OR(acf->seealso, "Not available"), 1);
   } else
#endif
   {
      synopsis_size = strlen(S_OR(acf->synopsis, "Not Available")) + AST_TERM_MAX_ESCAPE_CHARS;
      synopsis = ast_malloc(synopsis_size);

      description_size = strlen(S_OR(acf->desc, "Not Available")) + AST_TERM_MAX_ESCAPE_CHARS;
      description = ast_malloc(description_size);

      arguments_size = strlen(S_OR(acf->arguments, "Not Available")) + AST_TERM_MAX_ESCAPE_CHARS;
      arguments = ast_malloc(arguments_size);

      seealso_size = strlen(S_OR(acf->seealso, "Not Available")) + AST_TERM_MAX_ESCAPE_CHARS;
      seealso = ast_malloc(seealso_size);

      /* check allocated memory. */
      if (!synopsis || !description || !arguments || !seealso) {
         ast_free(synopsis);
         ast_free(description);
         ast_free(arguments);
         ast_free(seealso);
         ast_free(syntax);

         return CLI_FAILURE;
      }

      term_color(arguments, S_OR(acf->arguments, "Not available"), COLOR_CYAN, 0, arguments_size);
      term_color(synopsis, S_OR(acf->synopsis, "Not available"), COLOR_CYAN, 0, synopsis_size);
      term_color(description, S_OR(acf->desc, "Not available"), COLOR_CYAN, 0, description_size);
      term_color(seealso, S_OR(acf->seealso, "Not available"), COLOR_CYAN, 0, seealso_size);
   }

   ast_cli(a->fd, "%s%s%s\n\n%s%s\n\n%s%s\n\n%s%s\n\n%s%s\n",
         infotitle, syntitle, synopsis, destitle, description,
         stxtitle, syntax, argtitle, arguments, seealsotitle, seealso);

   ast_free(arguments);
   ast_free(synopsis);
   ast_free(description);
   ast_free(seealso);
   ast_free(syntax);

   return CLI_SUCCESS;
}

static struct ast_custom_function *ast_custom_function_find_nolock(const char *name)
{
   struct ast_custom_function *cur;
   int cmp;

   AST_RWLIST_TRAVERSE(&acf_root, cur, acflist) {
      cmp = strcmp(name, cur->name);
      if (cmp > 0) {
         continue;
      }
      if (!cmp) {
         /* Found it. */
         break;
      }
      /* Not in container. */
      cur = NULL;
      break;
   }

   return cur;
}

struct ast_custom_function *ast_custom_function_find(const char *name)
{
   struct ast_custom_function *acf;

   AST_RWLIST_RDLOCK(&acf_root);
   acf = ast_custom_function_find_nolock(name);
   AST_RWLIST_UNLOCK(&acf_root);

   return acf;
}

int ast_custom_function_unregister(struct ast_custom_function *acf)
{
   struct ast_custom_function *cur;

   if (!acf) {
      return -1;
   }

   AST_RWLIST_WRLOCK(&acf_root);
   cur = AST_RWLIST_REMOVE(&acf_root, acf, acflist);
   if (cur) {
#ifdef AST_XML_DOCS
      if (cur->docsrc == AST_XML_DOC) {
         ast_string_field_free_memory(acf);
      }
#endif
      ast_verb(2, "Unregistered custom function %s\n", cur->name);
   }
   AST_RWLIST_UNLOCK(&acf_root);

   return cur ? 0 : -1;
}

/*!
 * \brief Returns true if given custom function escalates privileges on read.
 *
 * \param acf Custom function to query.
 * \return True (non-zero) if reads escalate privileges.
 * \return False (zero) if reads just read.
 */
static int read_escalates(const struct ast_custom_function *acf)
{
   return acf->read_escalates;
}

/*!
 * \brief Returns true if given custom function escalates privileges on write.
 *
 * \param acf Custom function to query.
 * \return True (non-zero) if writes escalate privileges.
 * \return False (zero) if writes just write.
 */
static int write_escalates(const struct ast_custom_function *acf)
{
   return acf->write_escalates;
}

/*! \internal
 *  \brief Retrieve the XML documentation of a specified ast_custom_function,
 *         and populate ast_custom_function string fields.
 *  \param acf ast_custom_function structure with empty 'desc' and 'synopsis'
 *             but with a function 'name'.
 *  \retval -1 On error.
 *  \retval 0 On succes.
 */
static int acf_retrieve_docs(struct ast_custom_function *acf)
{
#ifdef AST_XML_DOCS
   char *tmpxml;

   /* Let's try to find it in the Documentation XML */
   if (!ast_strlen_zero(acf->desc) || !ast_strlen_zero(acf->synopsis)) {
      return 0;
   }

   if (ast_string_field_init(acf, 128)) {
      return -1;
   }

   /* load synopsis */
   tmpxml = ast_xmldoc_build_synopsis("function", acf->name, ast_module_name(acf->mod));
   ast_string_field_set(acf, synopsis, tmpxml);
   ast_free(tmpxml);

   /* load description */
   tmpxml = ast_xmldoc_build_description("function", acf->name, ast_module_name(acf->mod));
   ast_string_field_set(acf, desc, tmpxml);
   ast_free(tmpxml);

   /* load syntax */
   tmpxml = ast_xmldoc_build_syntax("function", acf->name, ast_module_name(acf->mod));
   ast_string_field_set(acf, syntax, tmpxml);
   ast_free(tmpxml);

   /* load arguments */
   tmpxml = ast_xmldoc_build_arguments("function", acf->name, ast_module_name(acf->mod));
   ast_string_field_set(acf, arguments, tmpxml);
   ast_free(tmpxml);

   /* load seealso */
   tmpxml = ast_xmldoc_build_seealso("function", acf->name, ast_module_name(acf->mod));
   ast_string_field_set(acf, seealso, tmpxml);
   ast_free(tmpxml);

   acf->docsrc = AST_XML_DOC;
#endif

   return 0;
}

int __ast_custom_function_register(struct ast_custom_function *acf, struct ast_module *mod)
{
   struct ast_custom_function *cur;

   if (!acf) {
      return -1;
   }

   acf->mod = mod;
#ifdef AST_XML_DOCS
   acf->docsrc = AST_STATIC_DOC;
#endif

   if (acf_retrieve_docs(acf)) {
      return -1;
   }

   AST_RWLIST_WRLOCK(&acf_root);

   cur = ast_custom_function_find_nolock(acf->name);
   if (cur) {
      ast_log(LOG_ERROR, "Function %s already registered.\n", acf->name);
      AST_RWLIST_UNLOCK(&acf_root);
      return -1;
   }

   /* Store in alphabetical order */
   AST_RWLIST_TRAVERSE_SAFE_BEGIN(&acf_root, cur, acflist) {
      if (strcmp(acf->name, cur->name) < 0) {
         AST_RWLIST_INSERT_BEFORE_CURRENT(acf, acflist);
         break;
      }
   }
   AST_RWLIST_TRAVERSE_SAFE_END;
   if (!cur) {
      AST_RWLIST_INSERT_TAIL(&acf_root, acf, acflist);
   }

   AST_RWLIST_UNLOCK(&acf_root);

   ast_verb(2, "Registered custom function '" COLORIZE_FMT "'\n", COLORIZE(COLOR_BRCYAN, 0, acf->name));

   return 0;
}

int __ast_custom_function_register_escalating(struct ast_custom_function *acf, enum ast_custom_function_escalation escalation, struct ast_module *mod)
{
   int res;

   res = __ast_custom_function_register(acf, mod);
   if (res != 0) {
      return -1;
   }

   switch (escalation) {
   case AST_CFE_NONE:
      break;
   case AST_CFE_READ:
      acf->read_escalates = 1;
      break;
   case AST_CFE_WRITE:
      acf->write_escalates = 1;
      break;
   case AST_CFE_BOTH:
      acf->read_escalates = 1;
      acf->write_escalates = 1;
      break;
   }

   return 0;
}

/*! \brief return a pointer to the arguments of the function,
 * and terminates the function name with '\\0'
 */
static char *func_args(char *function)
{
   char *args = strchr(function, '(');

   if (!args) {
      ast_log(LOG_WARNING, "Function '%s' doesn't contain parentheses.  Assuming null argument.\n", function);
   } else {
      char *p;
      *args++ = '\0';
      if ((p = strrchr(args, ')'))) {
         *p = '\0';
      } else {
         ast_log(LOG_WARNING, "Can't find trailing parenthesis for function '%s(%s'?\n", function, args);
      }
   }
   return args;
}

void pbx_live_dangerously(int new_live_dangerously)
{
   if (new_live_dangerously && !live_dangerously) {
      ast_log(LOG_WARNING, "Privilege escalation protection disabled!\n"
         "See https://wiki.asterisk.org/wiki/x/1gKfAQ for more details.\n");
   }

   if (!new_live_dangerously && live_dangerously) {
      ast_log(LOG_NOTICE, "Privilege escalation protection enabled.\n");
   }
   live_dangerously = new_live_dangerously;
}

int ast_thread_inhibit_escalations(void)
{
   int *thread_inhibit_escalations;

   thread_inhibit_escalations = ast_threadstorage_get(
      &thread_inhibit_escalations_tl, sizeof(*thread_inhibit_escalations));
   if (thread_inhibit_escalations == NULL) {
      ast_log(LOG_ERROR, "Error inhibiting privilege escalations for current thread\n");
      return -1;
   }

   *thread_inhibit_escalations = 1;
   return 0;
}

int ast_thread_inhibit_escalations_swap(int inhibit)
{
   int *thread_inhibit_escalations;
   int orig;

   thread_inhibit_escalations = ast_threadstorage_get(
      &thread_inhibit_escalations_tl, sizeof(*thread_inhibit_escalations));
   if (thread_inhibit_escalations == NULL) {
      ast_log(LOG_ERROR, "Error swapping privilege escalations inhibit for current thread\n");
      return -1;
   }

   orig = *thread_inhibit_escalations;
   *thread_inhibit_escalations = !!inhibit;
   return orig;
}

/*!
 * \brief Indicates whether the current thread inhibits the execution of
 * dangerous functions.
 *
 * \return True (non-zero) if dangerous function execution is inhibited.
 * \return False (zero) if dangerous function execution is allowed.
 */
static int thread_inhibits_escalations(void)
{
   int *thread_inhibit_escalations;

   thread_inhibit_escalations = ast_threadstorage_get(
      &thread_inhibit_escalations_tl, sizeof(*thread_inhibit_escalations));
   if (thread_inhibit_escalations == NULL) {
      ast_log(LOG_ERROR, "Error checking thread's ability to run dangerous functions\n");
      /* On error, assume that we are inhibiting */
      return 1;
   }

   return *thread_inhibit_escalations;
}

/*!
 * \brief Determines whether execution of a custom function's read function
 * is allowed.
 *
 * \param acfptr Custom function to check
 * \return True (non-zero) if reading is allowed.
 * \return False (zero) if reading is not allowed.
 */
static int is_read_allowed(struct ast_custom_function *acfptr)
{
   if (!acfptr) {
      return 1;
   }

   if (!read_escalates(acfptr)) {
      return 1;
   }

   if (!thread_inhibits_escalations()) {
      return 1;
   }

   if (live_dangerously) {
      /* Global setting overrides the thread's preference */
      ast_debug(2, "Reading %s from a dangerous context\n",
         acfptr->name);
      return 1;
   }

   /* We have no reason to allow this function to execute */
   return 0;
}

/*!
 * \brief Determines whether execution of a custom function's write function
 * is allowed.
 *
 * \param acfptr Custom function to check
 * \return True (non-zero) if writing is allowed.
 * \return False (zero) if writing is not allowed.
 */
static int is_write_allowed(struct ast_custom_function *acfptr)
{
   if (!acfptr) {
      return 1;
   }

   if (!write_escalates(acfptr)) {
      return 1;
   }

   if (!thread_inhibits_escalations()) {
      return 1;
   }

   if (live_dangerously) {
      /* Global setting overrides the thread's preference */
      ast_debug(2, "Writing %s from a dangerous context\n",
         acfptr->name);
      return 1;
   }

   /* We have no reason to allow this function to execute */
   return 0;
}

int ast_func_read(struct ast_channel *chan, const char *function, char *workspace, size_t len)
{
   char *copy = ast_strdupa(function);
   char *args = func_args(copy);
   struct ast_custom_function *acfptr = ast_custom_function_find(copy);
   int res;
   struct ast_module_user *u = NULL;

   if (acfptr == NULL) {
      ast_log(LOG_ERROR, "Function %s not registered\n", copy);
   } else if (!acfptr->read && !acfptr->read2) {
      ast_log(LOG_ERROR, "Function %s cannot be read\n", copy);
   } else if (!is_read_allowed(acfptr)) {
      ast_log(LOG_ERROR, "Dangerous function %s read blocked\n", copy);
   } else if (acfptr->read) {
      if (acfptr->mod) {
         u = __ast_module_user_add(acfptr->mod, chan);
      }
      res = acfptr->read(chan, copy, args, workspace, len);
      if (acfptr->mod && u) {
         __ast_module_user_remove(acfptr->mod, u);
      }

      return res;
   } else {
      struct ast_str *str = ast_str_create(16);

      if (acfptr->mod) {
         u = __ast_module_user_add(acfptr->mod, chan);
      }
      res = acfptr->read2(chan, copy, args, &str, 0);
      if (acfptr->mod && u) {
         __ast_module_user_remove(acfptr->mod, u);
      }
      ast_copy_string(workspace, ast_str_buffer(str), len > ast_str_size(str) ? ast_str_size(str) : len);
      ast_free(str);

      return res;
   }

   return -1;
}

int ast_func_read2(struct ast_channel *chan, const char *function, struct ast_str **str, ssize_t maxlen)
{
   char *copy = ast_strdupa(function);
   char *args = func_args(copy);
   struct ast_custom_function *acfptr = ast_custom_function_find(copy);
   int res;
   struct ast_module_user *u = NULL;

   if (acfptr == NULL) {
      ast_log(LOG_ERROR, "Function %s not registered\n", copy);
   } else if (!acfptr->read && !acfptr->read2) {
      ast_log(LOG_ERROR, "Function %s cannot be read\n", copy);
   } else if (!is_read_allowed(acfptr)) {
      ast_log(LOG_ERROR, "Dangerous function %s read blocked\n", copy);
   } else {
      if (acfptr->mod) {
         u = __ast_module_user_add(acfptr->mod, chan);
      }
      ast_str_reset(*str);
      if (acfptr->read2) {
         /* ast_str enabled */
         res = acfptr->read2(chan, copy, args, str, maxlen);
      } else {
         /* Legacy function pointer, allocate buffer for result */
         int maxsize = ast_str_size(*str);

         if (maxlen > -1) {
            if (maxlen == 0) {
               if (acfptr->read_max) {
                  maxsize = acfptr->read_max;
               } else {
                  maxsize = VAR_BUF_SIZE;
               }
            } else {
               maxsize = maxlen;
            }
            ast_str_make_space(str, maxsize);
         }
         res = acfptr->read(chan, copy, args, ast_str_buffer(*str), maxsize);
      }
      if (acfptr->mod && u) {
         __ast_module_user_remove(acfptr->mod, u);
      }

      return res;
   }

   return -1;
}

int ast_func_write(struct ast_channel *chan, const char *function, const char *value)
{
   char *copy = ast_strdupa(function);
   char *args = func_args(copy);
   struct ast_custom_function *acfptr = ast_custom_function_find(copy);

   if (acfptr == NULL) {
      ast_log(LOG_ERROR, "Function %s not registered\n", copy);
   } else if (!acfptr->write) {
      ast_log(LOG_ERROR, "Function %s cannot be written to\n", copy);
   } else if (!is_write_allowed(acfptr)) {
      ast_log(LOG_ERROR, "Dangerous function %s write blocked\n", copy);
   } else {
      int res;
      struct ast_module_user *u = NULL;

      if (acfptr->mod) {
         u = __ast_module_user_add(acfptr->mod, chan);
      }
      res = acfptr->write(chan, copy, args, value);
      if (acfptr->mod && u) {
         __ast_module_user_remove(acfptr->mod, u);
      }

      return res;
   }

   return -1;
}

static struct ast_cli_entry acf_cli[] = {
   AST_CLI_DEFINE(handle_show_functions, "Shows registered dialplan functions"),
   AST_CLI_DEFINE(handle_show_function, "Describe a specific dialplan function"),
};

static void unload_pbx_functions_cli(void)
{
   ast_cli_unregister_multiple(acf_cli, ARRAY_LEN(acf_cli));
}

int load_pbx_functions_cli(void)
{
   ast_cli_register_multiple(acf_cli, ARRAY_LEN(acf_cli));
   ast_register_cleanup(unload_pbx_functions_cli);

   return 0;
}