Patch "btrfs: Fix use-after-free when cleaning up fs_devs with a single stale device" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

btrfs: Fix use-after-free when cleaning up fs_devs with a single stale device

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
btrfs-fix-use-after-free-when-cleaning-up-fs_devs-with-a-single-stale-device.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Nikolay Borisov <[email protected]>
Date: Tue, 30 Jan 2018 16:07:37 +0200
Subject: btrfs: Fix use-after-free when cleaning up fs_devs with a single stale device

From: Nikolay Borisov <[email protected]>

commit fd649f10c3d21ee9d7542c609f29978bdf73ab94 upstream.

Commit 4fde46f0cc71 ("Btrfs: free the stale device") introduced btrfs_free_stale_device which iterates the device lists for all registered btrfs filesystems and deletes those devices which aren't mounted. In a btrfs_devices structure has only 1 device attached to it and it is unused then btrfs_free_stale_devices will proceed to also free the btrfs_fs_devices struct itself. Currently this leads to a use after free since list_for_each_entry will try to perform a check on the already freed memory to see if it has to terminate the loop.

The fix is to use 'break' when we know we are freeing the current fs_devs.

---
 fs/btrfs/volumes.c |    1 +
 1 file changed, 1 insertion(+)

@@ -568,6 +568,7 @@ void btrfs_free_stale_device(struct btrf
 				btrfs_sysfs_remove_fsid(fs_devs);
 				list_del(&fs_devs->list);
 				free_fs_devices(fs_devs);
+				break;
 			} else {
 				fs_devs->num_devices--;
 				list_del(&dev->dev_list);

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/btrfs-fix-use-after-free-when-cleaning-up-fs_devs-with-a-single-stale-device.patch