FAILED: Patch "btrfs: fix use-after-free of block device file in __btrfs_free_extra_devids()" failed to apply to v4.19-stable tree

The patch below does not apply to the v4.19-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

Thanks,
Sasha

------------------ original commit in Linus's tree ------------------

From aec8e6bf839101784f3ef037dcdb9432c3f32343 Mon Sep 17 00:00:00 2001
From: Zhihao Cheng <[email protected]>
Date: Mon, 21 Oct 2024 22:02:15 +0800
Subject: [PATCH] btrfs: fix use-after-free of block device file in
__btrfs_free_extra_devids()
MIME-Version: 1.0
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Content-Transfer-Encoding: 8bit

Mounting btrfs from two images (which have the same one fsid and two different dev_uuids) in certain executing order may trigger an UAF for variable 'device->bdev_file' in __btrfs_free_extra_devids(). And following are the details:

1. Attach image_1 to loop0, attach image_2 to loop1, and scan btrfs devices by ioctl(BTRFS_IOC_SCAN_DEV):

/ btrfs_device_1 → loop0
fs_device
\ btrfs_device_2 → loop1
2. mount /dev/loop0 /mnt
btrfs_open_devices

    btrfs_device_1->bdev_file = btrfs_get_bdev_and_sb(loop0)
    btrfs_device_2->bdev_file = btrfs_get_bdev_and_sb(loop1)
   btrfs_fill_super
    open_ctree
     fail: btrfs_close_devices // -ENOMEM
	    btrfs_close_bdev(btrfs_device_1)
             fput(btrfs_device_1->bdev_file)
	      // btrfs_device_1->bdev_file is freed
	    btrfs_close_bdev(btrfs_device_2)
             fput(btrfs_device_2->bdev_file)

3. mount /dev/loop1 /mnt
btrfs_open_devices

    btrfs_get_bdev_and_sb(&bdev_file)
     // EIO, btrfs_device_1->bdev_file is not assigned,
     // which points to a freed memory area
    btrfs_device_2->bdev_file = btrfs_get_bdev_and_sb(loop1)
   btrfs_fill_super
    open_ctree
     btrfs_free_extra_devids
      if (btrfs_device_1->bdev_file)
       fput(btrfs_device_1->bdev_file) // UAF !

Fix it by setting 'device->bdev_file' as 'NULL' after closing the btrfs_device in btrfs_close_one_device().

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

index 8f340ad1d9384..eb51b609190fb 100644
@@ -1105,6 +1105,7 @@ static void btrfs_close_one_device(struct btrfs_device *device)
 	if (device->bdev) {
 		fs_devices->open_devices--;
 		device->bdev = NULL;
+		device->bdev_file = NULL;
 	}
 	clear_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state);
 	btrfs_destroy_dev_zone_info(device);

2.43.0