pbx_functions.c

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/*
 * Asterisk -- An open source telephony toolkit.
 *
 * Copyright (C) 2015, CFWare, LLC
 *
 * Corey Farrell <git@cfware.com>
 *
 * 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 <git@cfware.com>
 */
 
/*** 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 *synopsis = NULL, *since = NULL, *description = NULL, *syntax = NULL, *arguments = NULL, *seealso = NULL;
    char *rtn = CLI_SUCCESS;
 
    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;
    }
 
#ifdef AST_XML_DOCS
    if (acf->docsrc == AST_XML_DOC) {
        synopsis = ast_xmldoc_printable(S_OR(acf->synopsis, "Not available"), 1);
        since = ast_xmldoc_printable(S_OR(acf->since, "Not available"), 1);
        description = ast_xmldoc_printable(S_OR(acf->desc, "Not available"), 1);
        syntax = ast_xmldoc_printable(S_OR(acf->syntax, "Not available"), 1);
        arguments = ast_xmldoc_printable(S_OR(acf->arguments, "Not available"), 1);
        seealso = ast_xmldoc_printable(S_OR(acf->seealso, "Not available"), 1);
    } else
#endif
    {
        synopsis = ast_strdup(S_OR(acf->synopsis, "Not Available"));
        since = ast_strdup(S_OR(acf->since, "Not Available"));
        description = ast_strdup(S_OR(acf->desc, "Not Available"));
        syntax = ast_strdup(S_OR(acf->syntax, "Not Available"));
        arguments = ast_strdup(S_OR(acf->arguments, "Not Available"));
        seealso = ast_strdup(S_OR(acf->seealso, "Not Available"));
    }
        /* check allocated memory. */
    if (!synopsis || !since || !description || !syntax || !arguments || !seealso) {
        rtn = CLI_FAILURE;
        goto free_docs;
    }
 
    ast_cli(a->fd, "\n"
        "%s  -= Info about Function '%s' =- %s\n\n"
        COLORIZE_FMT "\n"
        "%s\n\n"
        COLORIZE_FMT "\n"
        "%s\n\n"
        COLORIZE_FMT "\n"
        "%s\n\n"
        COLORIZE_FMT "\n"
        "%s\n\n"
        COLORIZE_FMT "\n"
        "%s\n\n"
        COLORIZE_FMT "\n"
        "%s\n\n",
        ast_term_color(COLOR_MAGENTA, 0), acf->name, ast_term_reset(),
        COLORIZE(COLOR_MAGENTA, 0, "[Synopsis]"), synopsis,
        COLORIZE(COLOR_MAGENTA, 0, "[Since]"), since,
        COLORIZE(COLOR_MAGENTA, 0, "[Description]"), description,
        COLORIZE(COLOR_MAGENTA, 0, "[Syntax]"), syntax,
        COLORIZE(COLOR_MAGENTA, 0, "[Arguments]"), arguments,
        COLORIZE(COLOR_MAGENTA, 0, "[See Also]"), seealso
        );
 
free_docs:
    ast_free(synopsis);
    ast_free(since);
    ast_free(description);
    ast_free(syntax);
    ast_free(arguments);
    ast_free(seealso);
 
    return rtn;
}
 
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(5, "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 success.
 */
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;
    }
 
    if (ast_string_field_init_extended(acf, since)) {
        ast_string_field_free_memory(acf);
        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 since */
    tmpxml = ast_xmldoc_build_since("function", acf->name, ast_module_name(acf->mod));
    ast_string_field_set(acf, since, 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(5, "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://docs.asterisk.org/Configuration/Dialplan/Privilege-Escalations-with-Dialplan-Functions/ 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);
            ast_str_update(*str); /* Manually set the string length */
        }
        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;
}