On Wed, Dec 16, 2020 at 07:17:08PM +0100, [email protected] wrote: > From: Martin Wilck <[email protected]> > > log_safe() could race with log_thread_stop(); simply > checking the value of log_thr has never been safe. By converting the > mutexes to static initializers, we avoid having to destroy them, and thus > possibly accessing a destroyed mutex in log_safe(). Furthermore, taking > both the logev_lock and the logq_lock makes sure the logarea isn't freed > while we are writing to it. > Reviewed-by: Benjamin Marzinski <[email protected]> > Signed-off-by: Martin Wilck <[email protected]> > --- > libmultipath/log_pthread.c | 48 +++++++++++++++++++++----------------- > 1 file changed, 26 insertions(+), 22 deletions(-) > > diff --git a/libmultipath/log_pthread.c b/libmultipath/log_pthread.c > index 3a2566a..0d48c52 100644 > --- a/libmultipath/log_pthread.c > +++ b/libmultipath/log_pthread.c > @@ -17,31 +17,42 @@ > > static pthread_t log_thr; > > -static pthread_mutex_t logq_lock; > -static pthread_mutex_t logev_lock; > -static pthread_cond_t logev_cond; > +/* logev_lock must not be taken with logq_lock held */ > +static pthread_mutex_t logq_lock = PTHREAD_MUTEX_INITIALIZER; > +static pthread_mutex_t logev_lock = PTHREAD_MUTEX_INITIALIZER; > +static pthread_cond_t logev_cond = PTHREAD_COND_INITIALIZER; > > static int logq_running; > static int log_messages_pending; > > void log_safe (int prio, const char * fmt, va_list ap) > { > + bool running; > + > if (prio > LOG_DEBUG) > prio = LOG_DEBUG; > > - if (log_thr == (pthread_t)0) { > - vsyslog(prio, fmt, ap); > - return; > - } > + /* > + * logev_lock protects logq_running. By holding it, we avoid a race > + * with log_thread_stop() -> log_close(), which would free the logarea. > + */ > + pthread_mutex_lock(&logev_lock); > + pthread_cleanup_push(cleanup_mutex, &logev_lock); > + running = logq_running; > > - pthread_mutex_lock(&logq_lock); > - log_enqueue(prio, fmt, ap); > - pthread_mutex_unlock(&logq_lock); > + if (running) { > + pthread_mutex_lock(&logq_lock); > + pthread_cleanup_push(cleanup_mutex, &logq_lock); > + log_enqueue(prio, fmt, ap); > + pthread_cleanup_pop(1); > > - pthread_mutex_lock(&logev_lock); > - log_messages_pending = 1; > - pthread_cond_signal(&logev_cond); > - pthread_mutex_unlock(&logev_lock); > + log_messages_pending = 1; > + pthread_cond_signal(&logev_cond); > + } > + pthread_cleanup_pop(1); > + > + if (!running) > + vsyslog(prio, fmt, ap); > } > > static void flush_logqueue (void) > @@ -103,9 +114,6 @@ void log_thread_start (pthread_attr_t *attr) > int running = 0; > > logdbg(stderr,"enter log_thread_start\n"); > - pthread_mutex_init(&logq_lock, NULL); > - pthread_mutex_init(&logev_lock, NULL); > - pthread_cond_init(&logev_cond, NULL); > > if (log_init("multipathd", 0)) { > fprintf(stderr,"can't initialize log buffer\n"); > @@ -154,13 +162,9 @@ void log_thread_stop (void) > } > pthread_cleanup_pop(1); > > - flush_logqueue(); > if (running) > pthread_join(log_thr, NULL); > > - pthread_mutex_destroy(&logq_lock); > - pthread_mutex_destroy(&logev_lock); > - pthread_cond_destroy(&logev_cond); > - > + flush_logqueue(); > log_close(); > } > -- > 2.29.0
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