linux-kernel - Re: [PATCH 1/5] security: allow finer granularity in permitting copy-up of security xattrs

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Date: Wed, 31 Jan 2024 15:25:29 +0200
From: Amir Goldstein <amir73il@...il.com>
To: Stefan Berger <stefanb@...ux.ibm.com>
Cc: linux-integrity@...r.kernel.org, linux-security-module@...r.kernel.org, 
	linux-unionfs@...r.kernel.org, linux-kernel@...r.kernel.org, 
	paul@...l-moore.com, jmorris@...ei.org, serge@...lyn.com, zohar@...ux.ibm.com, 
	roberto.sassu@...wei.com, miklos@...redi.hu, 
	Christian Brauner <brauner@...nel.org>
Subject: Re: [PATCH 1/5] security: allow finer granularity in permitting
 copy-up of security xattrs

On Tue, Jan 30, 2024 at 11:46 PM Stefan Berger <stefanb@...ux.ibm.com> wrote:
>
> Copying up xattrs is solely based on the security xattr name. For finer
> granularity add a dentry parameter to the security_inode_copy_up_xattr
> hook definition, allowing decisions to be based on the xattr content as
> well.
>
> Signed-off-by: Stefan Berger <stefanb@...ux.ibm.com>
> ---
>  fs/overlayfs/copy_up.c            | 2 +-
>  include/linux/evm.h               | 2 +-
>  include/linux/lsm_hook_defs.h     | 3 ++-
>  include/linux/security.h          | 4 ++--
>  security/integrity/evm/evm_main.c | 2 +-
>  security/security.c               | 7 ++++---
>  security/selinux/hooks.c          | 2 +-
>  security/smack/smack_lsm.c        | 2 +-
>  8 files changed, 13 insertions(+), 11 deletions(-)
>
> diff --git a/fs/overlayfs/copy_up.c b/fs/overlayfs/copy_up.c
> index b8e25ca51016..bd9ddcefb7a7 100644
> --- a/fs/overlayfs/copy_up.c
> +++ b/fs/overlayfs/copy_up.c
> @@ -114,7 +114,7 @@ int ovl_copy_xattr(struct super_block *sb, const struct path *oldpath, struct de
>                 if (ovl_is_private_xattr(sb, name))
>                         continue;
>
> -               error = security_inode_copy_up_xattr(name);
> +               error = security_inode_copy_up_xattr(old, name);

What do you think about:

                     error = security_inode_copy_up_xattr(name, NULL, 0);

and then later...

                     error = security_inode_copy_up_xattr(name, value, size);

I am asking because overlayfs uses mnt_idmap(path->mnt) and you
have used nop_mnt_idmap inside evm hook.
this does not look right to me?

Thanks,
Amir.