Re: [Fix CVE-2024-50217 in v6.6.y] [PATCH] btrfs: fix use-after-free of block device file in __btrfs_free_extra_devids()

[Greg KH <gregkh@linuxfoundation.org>]

On Mon, Feb 03, 2025 at 02:42:54AM -0800, Shubham Pushpkar wrote:
> From: Zhihao Cheng <chengzhihao1@huawei.com>
> 
> commit aec8e6bf839101784f3ef037dcdb9432c3f32343 ("btrfs:
> fix use-after-free of block device file in __btrfs_free_extra_devids()")
> 
> 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().
> 
> Fixes: CVE-2024-50217

Nit, as we assign CVEs _after_ a commit happens, there's no need to add
this to a commit here as it is implied by the assignment database of
cves-to-commits.

Also, any specific reason you didn't cc: everyone involved in this
commit for your backport as well?

thanks,

greg k-h