Re: [PATCH 10/12] ovl: take freeze protection when storing the uuid

[Amir Goldstein <amir73il@gmail.com>]

On Sat, Nov 14, 2026 at 11:47:17AM +0100, Christian Brauner wrote:
> ovl_init_uuid_xattr() stores the persistent uuid in an xattr on the
> upper root. That happens after ovl_make_workdir() dropped its write
> access to the upper mount and before ovl_get_indexdir() takes it
> again. So a freeze of the upper filesystem that lands in between lets
> the mount modify a frozen filesystem.
> 
> Take write access to the upper mount around the xattr update.
> 
> Fixes: d9544c1b0d9e ("ovl: store persistent uuid/fsid with uuid=on")
> Cc: stable@vger.kernel.org
> Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>

Reviewed-by: Amir Goldstein <amir73il@gmail.com>

Thanks,
Amir.

> ---
>  fs/overlayfs/util.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/overlayfs/util.c b/fs/overlayfs/util.c
> index 521717209b2e4..67aa7b71e9c83 100644
> --- a/fs/overlayfs/util.c
> +++ b/fs/overlayfs/util.c
> @@ -829,8 +829,12 @@ bool ovl_init_uuid_xattr(struct super_block *sb, struct ovl_fs *ofs,
>  
>  	/* Try to store persistent uuid */
>  	set = true;
> -	res = ovl_setxattr(ofs, upperpath->dentry, OVL_XATTR_UUID, uuid.b,
> -			   UUID_SIZE);
> +	res = mnt_want_write(ovl_upper_mnt(ofs));
> +	if (!res) {
> +		res = ovl_setxattr(ofs, upperpath->dentry, OVL_XATTR_UUID,
> +				   uuid.b, UUID_SIZE);
> +		mnt_drop_write(ovl_upper_mnt(ofs));
> +	}
>  	if (res)
>  		goto fail;
>  
> 
> -- 
> 2.53.0
>