Commit 9d118277 authored by Nick Mathewson's avatar Nick Mathewson 🥔
Browse files

Fix a rare infinite-recursion bug when shutting down. 

Once we had called log_free_all(), anything that tried to log a
message (like a failed tor_assert()) would fail like this:

   1. The logging call eventually invokes the _log() function.
   2. _log() calls tor_mutex_lock(log_mutex).
   3. tor_mutex_lock(m) calls tor_assert(m).
   4. Since we freed the log_mutex, tor_assert() fails, and tries to
      log its failure.
   5. GOTO 1.

Now we allocate the mutex statically, and never destroy it on
shutdown.

Bugfix on 0.2.0.16-alpha, which introduced the log mutex.

This bug was found by Matt Edman.
parent c9b8a4a1

ChangeLog

+3 −0
Original line number Diff line number Diff line
@@ -15,6 +15,9 @@ Changes in version 0.2.1.20 - 2009-??-?? 
    - Fix a signed/unsigned compile warning in 0.2.1.19.

    - Fix possible segmentation fault on directory authorities. Bugfix on

      0.2.1.14-rc.

    - Fix an extremely infinite recursion bug that could occur if we tried

      to log a message after shutting down the log subsystem.  Found by Matt

      Edman.  Bugfix on 0.2.0.16-alpha.





Changes in version 0.2.1.19 - 2009-07-28

src/common/log.c

+11 −7
Original line number Diff line number Diff line
@@ -94,7 +94,8 @@ should_log_function_name(log_domain_mask_t domain, int severity) 
}



/** A mutex to guard changes to logfiles and logging. */

static tor_mutex_t *log_mutex = NULL;

static tor_mutex_t log_mutex;

static int log_mutex_initialized = 0;



/** Linked list of logfile_t. */

static logfile_t *logfiles = NULL;
@@ -105,9 +106,9 @@ static int syslog_count = 0; 
#endif



#define LOCK_LOGS() STMT_BEGIN                                          \

  tor_mutex_acquire(log_mutex);                                         \

  tor_mutex_acquire(&log_mutex);                                        \

  STMT_END

#define UNLOCK_LOGS() STMT_BEGIN tor_mutex_release(log_mutex); STMT_END

#define UNLOCK_LOGS() STMT_BEGIN tor_mutex_release(&log_mutex); STMT_END



/** What's the lowest log level anybody cares about?  Checking this lets us

 * bail out early from log_debug if we aren't debugging.  */
@@ -448,8 +449,9 @@ logs_free_all(void) 
    log_free(victim);

  }

  tor_free(appname);

  tor_mutex_free(log_mutex);

  log_mutex = NULL;



  /* We _could_ destroy the log mutex here, but that would screw up any logs

   * that happened between here and the end of execution. */

}



/** Remove and free the log entry <b>victim</b> from the linked-list
@@ -545,8 +547,10 @@ add_stream_log(const log_severity_list_t *severity, 
void

init_logging(void)

{

  if (!log_mutex)

    log_mutex = tor_mutex_new();

  if (!log_mutex_initialized) {

    tor_mutex_init(&log_mutex);

    log_mutex_initialized = 1;

  }

}



/** Add a log handler to receive messages during startup (before the real