[dm-devel] [PATCH] multipathd: avoid crash in uevent_cleanup()

[mwilck at suse.com]

From: Martin Wilck <mwilck at suse.com>

Crashes have been observed in the unwinder stack of uevent_listen().
This can only be explained by "udev" not being a valid object at that
time. Be sure to pass a valid pointer, and don't call udev_unref() if
it has been set to NULL already.

I'm not quite sure how this would come to pass, as we join the threads
before setting udev to NULL, but this is unwinder code, so I guess it
might actually be executed after the thread has terminated.

Signed-off-by: Martin Wilck <mwilck at suse.com>
---
 libmultipath/uevent.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/libmultipath/uevent.c b/libmultipath/uevent.c
index d3061bf..4e662ff 100644
--- a/libmultipath/uevent.c
+++ b/libmultipath/uevent.c
@@ -397,10 +397,11 @@ service_uevq(struct list_head *tmpq)
 
 static void uevent_cleanup(void *arg)
 {
-	struct udev *udev = arg;
+	struct udev **pudev = arg;
 
+	if (*pudev)
+		udev_unref(*pudev);
 	condlog(3, "Releasing uevent_listen() resources");
-	udev_unref(udev);
 }
 
 static void monitor_cleanup(void *arg)
@@ -560,7 +561,7 @@ int uevent_listen(struct udev *udev)
 		return 1;
 	}
 	udev_ref(udev);
-	pthread_cleanup_push(uevent_cleanup, udev);
+	pthread_cleanup_push(uevent_cleanup, &udev);
 
 	monitor = udev_monitor_new_from_netlink(udev, "udev");
 	if (!monitor) {
-- 
2.29.2