Re: [PATCH 5/6] ovl: use vfs_set_acl_prepare()

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[Sorry, forgot to Cc ovl developers on accident.]

On Mon, Aug 29, 2022 at 02:38:44PM +0200, Christian Brauner wrote:
> The posix_acl_from_xattr() helper should mainly be used in
> i_op->get_acl() handlers. It translates from the uapi struct into the
> kernel internal POSIX ACL representation and doesn't care about mount
> idmappings.
> 
> Use the vfs_set_acl_prepare() helper to generate a kernel internal POSIX
> ACL representation in struct posix_acl format taking care to map from
> the mount idmapping into the filesystem's idmapping.
> 
> The returned struct posix_acl is in the correct format to be cached by
> the VFS or passed to the filesystem's i_op->set_acl() method to write to
> the backing store.
> 
> Signed-off-by: Christian Brauner (Microsoft) <brauner@xxxxxxxxxx>
> ---
>  fs/overlayfs/super.c | 15 ++++++++++++++-
>  1 file changed, 14 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
> index ec746d447f1b..5da771b218d1 100644
> --- a/fs/overlayfs/super.c
> +++ b/fs/overlayfs/super.c
> @@ -1022,7 +1022,20 @@ ovl_posix_acl_xattr_set(const struct xattr_handler *handler,
>  
>  	/* Check that everything is OK before copy-up */
>  	if (value) {
> -		acl = posix_acl_from_xattr(&init_user_ns, value, size);
> +		/* The above comment can be understood in two ways:
> +		 *
> +		 * 1. We just want to check whether the basic POSIX ACL format
> +		 *    is ok. For example, if the header is correct and the size
> +		 *    is sane.
> +		 * 2. We want to know whether the ACL_{GROUP,USER} entries can
> +		 *    be mapped according to the underlying filesystem.
> +		 *
> +		 * Currently, we only check 1. If we wanted to check 2. we
> +		 * would need to pass the mnt_userns and the fs_userns of the
> +		 * underlying filesystem. But frankly, I think checking 1. is
> +		 * enough to start the copy-up.
> +		 */
> +		acl = vfs_set_acl_prepare(&init_user_ns, &init_user_ns, value, size);
>  		if (IS_ERR(acl))
>  			return PTR_ERR(acl);
>  	}
> -- 
> 2.34.1
> 



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