Re: [PATCH v2 5/5] ovl: don't require "metacopy=on" for "verity"

[Alexander Larsson <alexl@redhat.com>]

On Tue, 2025-03-25 at 11:46 +0100, Miklos Szeredi wrote:
> Allow the "verity" mount option to be used with "userxattr" data-only
> layer(s).
> 
> Previous patches made sure that with "userxattr" metacopy only works
> in the
> lower -> data scenario.
> 
> In this scenario the lower (metadata) layer must be secured against
> tampering, in which case the verity checksums contained in this layer
> can
> ensure integrity of data even in the case of an untrusted data layer.
> 
> Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

Reviewed-by: Alexander Larsson <alexl@redhat.com>

This works well enough for composefs, but I agree with Amir that once
we start allowing redirects into data-only lowers, even with
metacopy=0, then we could at least allow verity=on.

> ---
>  fs/overlayfs/params.c | 11 +++--------
>  1 file changed, 3 insertions(+), 8 deletions(-)
> 
> diff --git a/fs/overlayfs/params.c b/fs/overlayfs/params.c
> index 54468b2b0fba..8ac0997dca13 100644
> --- a/fs/overlayfs/params.c
> +++ b/fs/overlayfs/params.c
> @@ -846,8 +846,8 @@ int ovl_fs_params_verify(const struct
> ovl_fs_context *ctx,
>  		config->uuid = OVL_UUID_NULL;
>  	}
>  
> -	/* Resolve verity -> metacopy dependency */
> -	if (config->verity_mode && !config->metacopy) {
> +	/* Resolve verity -> metacopy dependency (unless used with
> userxattr) */
> +	if (config->verity_mode && !config->metacopy && !config-
> >userxattr) {
>  		/* Don't allow explicit specified conflicting
> combinations */
>  		if (set.metacopy) {
>  			pr_err("conflicting options:
> metacopy=off,verity=%s\n",
> @@ -945,7 +945,7 @@ int ovl_fs_params_verify(const struct
> ovl_fs_context *ctx,
>  	}
>  
>  
> -	/* Resolve userxattr -> !redirect && !metacopy && !verity
> dependency */
> +	/* Resolve userxattr -> !redirect && !metacopy dependency */
>  	if (config->userxattr) {
>  		if (set.redirect &&
>  		    config->redirect_mode != OVL_REDIRECT_NOFOLLOW)
> {
> @@ -957,11 +957,6 @@ int ovl_fs_params_verify(const struct
> ovl_fs_context *ctx,
>  			pr_err("conflicting options:
> userxattr,metacopy=on\n");
>  			return -EINVAL;
>  		}
> -		if (config->verity_mode) {
> -			pr_err("conflicting options:
> userxattr,verity=%s\n",
> -			       ovl_verity_mode(config));
> -			return -EINVAL;
> -		}
>  		/*
>  		 * Silently disable default setting of redirect and
> metacopy.
>  		 * This shall be the default in the future as well:
> these

-- 
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=-=-=
 Alexander Larsson                                            Red Hat,
Inc 
       alexl@redhat.com            alexander.larsson@gmail.com 
He's an oversexed soccer-playing filmmaker possessed of the uncanny 
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of 
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