xs: make sure mutexes are cleaned up and memory freed if the read thread is cancelled

If the read thread is terminated with pthread cancel, it must make
sure all memory is freed and mutexes are unlocked.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>

1 files changed, 30 insertions, 16 deletions

diff --git a/tools/xenstore/xs.c b/tools/xenstore/xs.c
index 5b05268481..6a87ccf708 100644
--- a/tools/xenstore/xs.c
+++ b/tools/xenstore/xs.c
@@ -85,6 +85,8 @@ struct xs_handle {
 #define mutex_unlock(m)		pthread_mutex_unlock(m)
 #define condvar_signal(c)	pthread_cond_signal(c)
 #define condvar_wait(c,m,hnd)	pthread_cond_wait(c,m)
+#define cleanup_push(f, a)	pthread_cleanup_push((void (*)(void *))(f), (void *)(a))
+#define cleanup_pop(run)	pthread_cleanup_pop(run)
 
 static void *read_thread(void *arg);
 
@@ -102,6 +104,8 @@ struct xs_handle {
 #define mutex_unlock(m)		((void)0)
 #define condvar_signal(c)	((void)0)
 #define condvar_wait(c,m,hnd)	read_message(hnd)
+#define cleanup_push(f, a)	((void)0)
+#define cleanup_pop(run)	((void)0)
 
 #endif
 
@@ -262,7 +266,6 @@ void xs_daemon_close(struct xs_handle *h)
 
 #ifdef USE_PTHREAD
 	if (h->read_thr_exists) {
-		/* XXX FIXME: May leak an unpublished message buffer. */
 		pthread_cancel(h->read_thr);
 		pthread_join(h->read_thr, NULL);
 	}
@@ -860,44 +863,53 @@ static int read_message(struct xs_handle *h)
 {
 	struct xs_stored_msg *msg = NULL;
 	char *body = NULL;
-	int saved_errno;
+	int saved_errno = 0;
+	int ret = -1;
 
 	/* Allocate message structure and read the message header. */
 	msg = malloc(sizeof(*msg));
 	if (msg == NULL)
 		goto error;
-	if (!read_all(h->fd, &msg->hdr, sizeof(msg->hdr)))
-		goto error;
+	cleanup_push(free, msg);
+	if (!read_all(h->fd, &msg->hdr, sizeof(msg->hdr))) { /* Cancellation point */
+		saved_errno = errno;
+		goto error_freemsg;
+	}
 
 	/* Allocate and read the message body. */
 	body = msg->body = malloc(msg->hdr.len + 1);
 	if (body == NULL)
-		goto error;
-	if (!read_all(h->fd, body, msg->hdr.len))
-		goto error;
+		goto error_freemsg;
+	cleanup_push(free, body);
+	if (!read_all(h->fd, body, msg->hdr.len)) { /* Cancellation point */
+		saved_errno = errno;
+		goto error_freebody;
+	}
+
 	body[msg->hdr.len] = '\0';
 
 	if (msg->hdr.type == XS_WATCH_EVENT) {
 		mutex_lock(&h->watch_mutex);
+		cleanup_push(pthread_mutex_unlock, &h->watch_mutex);
 
 		/* Kick users out of their select() loop. */
 		if (list_empty(&h->watch_list) &&
 		    (h->watch_pipe[1] != -1))
-			while (write(h->watch_pipe[1], body, 1) != 1)
+			while (write(h->watch_pipe[1], body, 1) != 1) /* Cancellation point */
 				continue;
 
 		list_add_tail(&msg->list, &h->watch_list);
 
 		condvar_signal(&h->watch_condvar);
 
-		mutex_unlock(&h->watch_mutex);
+		cleanup_pop(1);
 	} else {
 		mutex_lock(&h->reply_mutex);
 
 		/* There should only ever be one response pending! */
 		if (!list_empty(&h->reply_list)) {
 			mutex_unlock(&h->reply_mutex);
-			goto error;
+			goto error_freebody;
 		}
 
 		list_add_tail(&msg->list, &h->reply_list);
@@ -906,14 +918,16 @@ static int read_message(struct xs_handle *h)
 		mutex_unlock(&h->reply_mutex);
 	}
 
-	return 0;
+	ret = 0;
 
- error:
-	saved_errno = errno;
-	free(msg);
-	free(body);
+error_freebody:
+	cleanup_pop(ret == -1);
+error_freemsg:
+	cleanup_pop(ret == -1);
+error:
 	errno = saved_errno;
-	return -1;
+
+	return ret;
 }
 
 #ifdef USE_PTHREAD