linux-kernel - Re: [PATCH] fs: Reorder inode_owner_or

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Date:   Tue, 20 Jun 2017 17:02:50 -0500
From:   "Serge E. Hallyn" <serge@...lyn.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Solar Designer <solar@...nwall.com>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Andy Lutomirski <luto@...nel.org>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fs: Reorder inode_owner_or_capable() to avoid needless

Quoting Kees Cook (keescook@...omium.org):
> Checking for capabilities should be the last operation when performing
> access control tests so that PF_SUPERPRIV is set only when it was required
> for success (implying that the capability was needed for the operation).
> 
> Reported-by: Solar Designer <solar@...nwall.com>
> Cc: Serge E. Hallyn <serge@...lyn.com>

Makes sense, thanks.

Acked-by: Serge Hallyn <serge@...lyn.com>

> Cc: Andy Lutomirski <luto@...nel.org>
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
>  fs/inode.c | 2 +-
>  fs/namei.c | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/inode.c b/fs/inode.c
> index db5914783a71..7092debe90cc 100644
> --- a/fs/inode.c
> +++ b/fs/inode.c
> @@ -2023,7 +2023,7 @@ bool inode_owner_or_capable(const struct inode *inode)
>  		return true;
>  
>  	ns = current_user_ns();
> -	if (ns_capable(ns, CAP_FOWNER) && kuid_has_mapping(ns, inode->i_uid))
> +	if (kuid_has_mapping(ns, inode->i_uid) && ns_capable(ns, CAP_FOWNER))
>  		return true;
>  	return false;
>  }
> diff --git a/fs/namei.c b/fs/namei.c
> index 6571a5f5112e..efe53a5d0737 100644
> --- a/fs/namei.c
> +++ b/fs/namei.c
> @@ -1008,7 +1008,7 @@ static int may_linkat(struct path *link)
>  	/* Source inode owner (or CAP_FOWNER) can hardlink all they like,
>  	 * otherwise, it must be a safe source.
>  	 */
> -	if (inode_owner_or_capable(inode) || safe_hardlink_source(inode))
> +	if (safe_hardlink_source(inode) || inode_owner_or_capable(inode))
>  		return 0;
>  
>  	audit_log_link_denied("linkat", link);
> -- 
> 2.7.4
> 
> 
> -- 
> Kees Cook
> Pixel Security