tor

compat_libevent.c (15076B)

---

/* Copyright (c) 2009-2021, The Tor Project, Inc. */
/* See LICENSE for licensing information */

/**
* \file compat_libevent.c
* \brief Wrappers and utility functions for Libevent.
*/

#include "orconfig.h"
#define COMPAT_LIBEVENT_PRIVATE
#include "lib/evloop/compat_libevent.h"

#include "lib/crypt_ops/crypto_rand.h"
#include "lib/log/log.h"
#include "lib/log/util_bug.h"
#include "lib/string/compat_string.h"

#include <event2/event.h>
#include <event2/thread.h>
#include <string.h>

/** A string which, if it appears in a libevent log, should be ignored. */
static const char *suppress_msg = NULL;
/** Callback function passed to event_set_log() so we can intercept
* log messages from libevent. */
STATIC void
libevent_logging_callback(int severity, const char *msg)
{
 char buf[1024];
 size_t n;
 if (suppress_msg && strstr(msg, suppress_msg))
   return;
 n = strlcpy(buf, msg, sizeof(buf));
 if (n && n < sizeof(buf) && buf[n-1] == '\n') {
   buf[n-1] = '\0';
 }
 switch (severity) {
   case _EVENT_LOG_DEBUG:
     log_debug(LD_NOCB|LD_NET, "Message from libevent: %s", buf);
     break;
   case _EVENT_LOG_MSG:
     log_info(LD_NOCB|LD_NET, "Message from libevent: %s", buf);
     break;
   case _EVENT_LOG_WARN:
     log_warn(LD_NOCB|LD_GENERAL, "Warning from libevent: %s", buf);
     break;
   case _EVENT_LOG_ERR:
     log_err(LD_NOCB|LD_GENERAL, "Error from libevent: %s", buf);
     break;
   default:
     log_warn(LD_NOCB|LD_GENERAL, "Message [%d] from libevent: %s",
         severity, buf);
     break;
 }
}
/** Set hook to intercept log messages from libevent. */
void
configure_libevent_logging(void)
{
 event_set_log_callback(libevent_logging_callback);
}

/** Ignore any libevent log message that contains <b>msg</b>. */
void
suppress_libevent_log_msg(const char *msg)
{
 suppress_msg = msg;
}

/* Wrapper for event_free() that tolerates tor_event_free(NULL) */
void
tor_event_free_(struct event *ev)
{
 if (ev == NULL)
   return;
 event_free(ev);
}

/** Global event base for use by the main thread. */
static struct event_base *the_event_base = NULL;

/**
* @defgroup postloop post-loop event helpers
*
* If we're not careful, Libevent can susceptible to infinite event chains:
* one event can activate another, whose callback activates another, whose
* callback activates another, ad infinitum.  While this is happening,
* Libevent won't be checking timeouts, socket-based events, signals, and so
* on.
*
* We solve this problem by marking some events as "post-loop".  A post-loop
* event behaves like any ordinary event, but any events that _it_ activates
* cannot run until Libevent has checked for other events at least once.
*
* @{ */

/**
* An event that stops Libevent from running any more events on the current
* iteration of its loop, until it has re-checked for socket events, signal
* events, timeouts, etc.
*/
static struct event *rescan_mainloop_ev = NULL;

/**
* Callback to implement rescan_mainloop_ev: it simply exits the mainloop,
* and relies on Tor to re-enter the mainloop since no error has occurred.
*/
static void
rescan_mainloop_cb(evutil_socket_t fd, short events, void *arg)
{
 (void)fd;
 (void)events;
 struct event_base *the_base = arg;
 event_base_loopbreak(the_base);
}

/** @} */

/* This is what passes for version detection on OSX.  We set
* MACOSX_KQUEUE_IS_BROKEN to true iff we're on a version of OSX before
* 10.4.0 (aka 1040). */
#ifdef __APPLE__
#ifdef __ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__
#define MACOSX_KQUEUE_IS_BROKEN \
 (__ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__ < 1040)
#else
#define MACOSX_KQUEUE_IS_BROKEN 0
#endif /* defined(__ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__) */
#endif /* defined(__APPLE__) */

/** Initialize the Libevent library and set up the event base. */
void
tor_libevent_initialize(tor_libevent_cfg_t *torcfg)
{
 tor_assert(the_event_base == NULL);
 /* some paths below don't use torcfg, so avoid unused variable warnings */
 (void)torcfg;

 {
   struct event_config *cfg;

   cfg = event_config_new();
   tor_assert(cfg);

   /* Telling Libevent not to try to turn locking on can avoid a needless
    * socketpair() attempt. */
   event_config_set_flag(cfg, EVENT_BASE_FLAG_NOLOCK);

   if (torcfg->num_cpus > 0)
     event_config_set_num_cpus_hint(cfg, torcfg->num_cpus);

   /* We can enable changelist support with epoll, since we don't give
    * Libevent any dup'd fds.  This lets us avoid some syscalls. */
   event_config_set_flag(cfg, EVENT_BASE_FLAG_EPOLL_USE_CHANGELIST);

   the_event_base = event_base_new_with_config(cfg);

   event_config_free(cfg);
 }

 if (!the_event_base) {
   /* LCOV_EXCL_START */
   log_err(LD_GENERAL, "Unable to initialize Libevent: cannot continue.");
   exit(1); // exit ok: libevent is broken.
   /* LCOV_EXCL_STOP */
 }

 rescan_mainloop_ev = event_new(the_event_base, -1, 0,
                                rescan_mainloop_cb, the_event_base);
 if (!rescan_mainloop_ev) {
   /* LCOV_EXCL_START */
   log_err(LD_GENERAL, "Unable to create rescan event: cannot continue.");
   exit(1); // exit ok: libevent is broken.
   /* LCOV_EXCL_STOP */
 }

 log_info(LD_GENERAL,
     "Initialized libevent version %s using method %s. Good.",
     event_get_version(), tor_libevent_get_method());
}

/**
* Return true iff the libevent module has been successfully initialized,
* and not subsequently shut down.
**/
bool
tor_libevent_is_initialized(void)
{
 return the_event_base != NULL;
}

/** Return the current Libevent event base that we're set up to use. */
MOCK_IMPL(struct event_base *,
tor_libevent_get_base, (void))
{
 tor_assert(the_event_base != NULL);
 return the_event_base;
}

/** Return the name of the Libevent backend we're using. */
const char *
tor_libevent_get_method(void)
{
 return event_base_get_method(the_event_base);
}

/** Return a string representation of the version of the currently running
* version of Libevent. */
const char *
tor_libevent_get_version_str(void)
{
 return event_get_version();
}

/** Return a string representation of the version of Libevent that was used
* at compilation time. */
const char *
tor_libevent_get_header_version_str(void)
{
 return LIBEVENT_VERSION;
}

/** Represents a timer that's run every N microseconds by Libevent. */
struct periodic_timer_t {
 /** Underlying event used to implement this periodic event. */
 struct event *ev;
 /** The callback we'll be invoking whenever the event triggers */
 void (*cb)(struct periodic_timer_t *, void *);
 /** User-supplied data for the callback */
 void *data;
};

/** Libevent callback to implement a periodic event. */
static void
periodic_timer_cb(evutil_socket_t fd, short what, void *arg)
{
 periodic_timer_t *timer = arg;
 (void) what;
 (void) fd;
 timer->cb(timer, timer->data);
}

/** Create and schedule a new timer that will run every <b>tv</b> in
* the event loop of <b>base</b>.  When the timer fires, it will
* run the timer in <b>cb</b> with the user-supplied data in <b>data</b>. */
periodic_timer_t *
periodic_timer_new(struct event_base *base,
                  const struct timeval *tv,
                  void (*cb)(periodic_timer_t *timer, void *data),
                  void *data)
{
 periodic_timer_t *timer;
 tor_assert(base);
 tor_assert(tv);
 tor_assert(cb);
 timer = tor_malloc_zero(sizeof(periodic_timer_t));
 if (!(timer->ev = tor_event_new(base, -1, EV_PERSIST,
                                 periodic_timer_cb, timer))) {
   tor_free(timer);
   return NULL;
 }
 timer->cb = cb;
 timer->data = data;
 periodic_timer_launch(timer, tv);
 return timer;
}

/**
* Launch the timer <b>timer</b> to run at <b>tv</b> from now, and every
* <b>tv</b> thereafter.
*
* If the timer is already enabled, this function does nothing.
*/
void
periodic_timer_launch(periodic_timer_t *timer, const struct timeval *tv)
{
 tor_assert(timer);
 if (event_pending(timer->ev, EV_TIMEOUT, NULL))
   return;
 event_add(timer->ev, tv);
}

/**
* Disable the provided <b>timer</b>, but do not free it.
*
* You can reenable the same timer later with periodic_timer_launch.
*
* If the timer is already disabled, this function does nothing.
*/
void
periodic_timer_disable(periodic_timer_t *timer)
{
 tor_assert(timer);
 (void) event_del(timer->ev);
}

/** Stop and free a periodic timer */
void
periodic_timer_free_(periodic_timer_t *timer)
{
 if (!timer)
   return;
 tor_event_free(timer->ev);
 tor_free(timer);
}

/**
* Type used to represent events that run directly from the main loop,
* either because they are activated from elsewhere in the code, or
* because they have a simple timeout.
*
* We use this type to avoid exposing Libevent's API throughout the rest
* of the codebase.
*
* This type can't be used for all events: it doesn't handle events that
* are triggered by signals or by sockets.
*/
struct mainloop_event_t {
 struct event *ev;
 void (*cb)(mainloop_event_t *, void *);
 void *userdata;
};

/**
* Internal: Implements mainloop event using a libevent event.
*/
static void
mainloop_event_cb(evutil_socket_t fd, short what, void *arg)
{
 (void)fd;
 (void)what;
 mainloop_event_t *mev = arg;
 mev->cb(mev, mev->userdata);
}

/**
* As mainloop_event_cb, but implements a post-loop event.
*/
static void
mainloop_event_postloop_cb(evutil_socket_t fd, short what, void *arg)
{
 (void)fd;
 (void)what;

 /* Note that if rescan_mainloop_ev is already activated,
  * event_active() will do nothing: only the first post-loop event that
  * happens each time through the event loop will cause it to be
  * activated.
  *
  * Because event_active() puts events on a FIFO queue, every event
  * that is made active _after_ rescan_mainloop_ev will get its
  * callback run after rescan_mainloop_cb is called -- that is, on the
  * next iteration of the loop.
  */
 event_active(rescan_mainloop_ev, EV_READ, 1);

 mainloop_event_t *mev = arg;
 mev->cb(mev, mev->userdata);
}

/**
* Helper for mainloop_event_new() and mainloop_event_postloop_new().
*/
static mainloop_event_t *
mainloop_event_new_impl(int postloop,
                       void (*cb)(mainloop_event_t *, void *),
                       void *userdata)
{
 tor_assert(cb);

 struct event_base *base = tor_libevent_get_base();
 mainloop_event_t *mev = tor_malloc_zero(sizeof(mainloop_event_t));
 mev->ev = tor_event_new(base, -1, 0,
                 postloop ? mainloop_event_postloop_cb : mainloop_event_cb,
                 mev);
 tor_assert(mev->ev);
 mev->cb = cb;
 mev->userdata = userdata;
 return mev;
}

/**
* Create and return a new mainloop_event_t to run the function <b>cb</b>.
*
* When run, the callback function will be passed the mainloop_event_t
* and <b>userdata</b> as its arguments.  The <b>userdata</b> pointer
* must remain valid for as long as the mainloop_event_t event exists:
* it is your responsibility to free it.
*
* The event is not scheduled by default: Use mainloop_event_activate()
* or mainloop_event_schedule() to make it run.
*/
mainloop_event_t *
mainloop_event_new(void (*cb)(mainloop_event_t *, void *),
                  void *userdata)
{
 return mainloop_event_new_impl(0, cb, userdata);
}

/**
* As mainloop_event_new(), but create a post-loop event.
*
* A post-loop event behaves like any ordinary event, but any events
* that _it_ activates cannot run until Libevent has checked for other
* events at least once.
*/
mainloop_event_t *
mainloop_event_postloop_new(void (*cb)(mainloop_event_t *, void *),
                           void *userdata)
{
 return mainloop_event_new_impl(1, cb, userdata);
}

/**
* Schedule <b>event</b> to run in the main loop, immediately.  If it is
* not scheduled, it will run anyway. If it is already scheduled to run
* later, it will run now instead.  This function will have no effect if
* the event is already scheduled to run.
*
* This function may only be called from the main thread.
*/
void
mainloop_event_activate(mainloop_event_t *event)
{
 tor_assert(event);
 event_active(event->ev, EV_READ, 1);
}

/** Schedule <b>event</b> to run in the main loop, after a delay of <b>tv</b>.
*
* If the event is scheduled for a different time, cancel it and run
* after this delay instead.  If the event is currently pending to run
* <b>now</b>, has no effect.
*
* Do not call this function with <b>tv</b> == NULL -- use
* mainloop_event_activate() instead.
*
* This function may only be called from the main thread.
*/
int
mainloop_event_schedule(mainloop_event_t *event, const struct timeval *tv)
{
 tor_assert(event);
 if (BUG(tv == NULL)) {
   // LCOV_EXCL_START
   mainloop_event_activate(event);
   return 0;
   // LCOV_EXCL_STOP
 }
 return event_add(event->ev, tv);
}

/** Cancel <b>event</b> if it is currently active or pending. (Do nothing if
* the event is not currently active or pending.) */
void
mainloop_event_cancel(mainloop_event_t *event)
{
 if (!event)
   return;
 (void) event_del(event->ev);
}

/** Cancel <b>event</b> and release all storage associated with it. */
void
mainloop_event_free_(mainloop_event_t *event)
{
 if (!event)
   return;
 tor_event_free(event->ev);
 memset(event, 0xb8, sizeof(*event));
 tor_free(event);
}

int
tor_init_libevent_rng(void)
{
 int rv = 0;
 char buf[256];
 if (evutil_secure_rng_init() < 0) {
   rv = -1;
 }
 crypto_rand(buf, 32);
#ifdef HAVE_EVUTIL_SECURE_RNG_ADD_BYTES
 evutil_secure_rng_add_bytes(buf, 32);
#endif
 evutil_secure_rng_get_bytes(buf, sizeof(buf));
 return rv;
}

/**
* Un-initialize libevent in preparation for an exit
*/
void
tor_libevent_free_all(void)
{
 tor_event_free(rescan_mainloop_ev);
 if (the_event_base)
   event_base_free(the_event_base);
 the_event_base = NULL;
}

/**
* Run the event loop for the provided event_base, handling events until
* something stops it.  If <b>once</b> is set, then just poll-and-run
* once, then exit.  Return 0 on success, -1 if an error occurred, or 1
* if we exited because no events were pending or active.
*
* This isn't reentrant or multithreaded.
*/
int
tor_libevent_run_event_loop(struct event_base *base, int once)
{
 const int flags = once ? EVLOOP_ONCE : 0;
 return event_base_loop(base, flags);
}

/** Tell the event loop to exit after <b>delay</b>.  If <b>delay</b> is NULL,
* instead exit after we're done running the currently active events. */
void
tor_libevent_exit_loop_after_delay(struct event_base *base,
                                  const struct timeval *delay)
{
 event_base_loopexit(base, delay);
}

/** Tell the event loop to exit after running whichever callback is currently
* active. */
void
tor_libevent_exit_loop_after_callback(struct event_base *base)
{
 event_base_loopbreak(base);
}

#if defined(TOR_UNIT_TESTS)
/** For testing: called post-fork to make libevent reinitialize
* kernel structures. */
void
tor_libevent_postfork(void)
{
 int r = event_reinit(tor_libevent_get_base());
 tor_assert(r == 0);
}
#endif /* defined(TOR_UNIT_TESTS) */