From: Casey Schaufler <casey@schaufler-ca.com>
Subject: Re: [kernel-hardening] [RFC PATCH 1/2] security, capabilities: create
 CAP_TRUSTED
Date: Sat, 21 Oct 2017 10:25:21 -0700
Message-ID: <d3e1c911-138d-082a-b941-651217d0faf8@schaufler-ca.com>
References: <20171021134558.21195-1-nicolas@belouin.fr>
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To: Nicolas Belouin <nicolas@belouin.fr>, Jan Kara <jack@suse.com>,
        Theodore Ts'o <tytso@mit.edu>,
        Andreas Dilger <adilger.kernel@dilger.ca>,
        Jaegeuk Kim <jaegeuk@kernel.org>, Chao Yu <yuchao0@huawei.com>,
        David Woodhouse <dwmw2@infradead.org>,
        Dave Kleikamp <shaggy@kernel.org>,
        Mark Fasheh <mfasheh@versity.com>,
        Joel Becker <jlbec@evilplan.org>,
        Miklos Szeredi <miklos@szeredi.hu>,
        Phillip Lougher <phillip@squashfs.org.uk>,
        Richard Weinberger <richard@nod.at>,
        Artem Bityutskiy <dedekind1@gmail.com>,
        Adrian Hunter <adrian.hunter@intel.com>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Serge Hallyn <serge@hallyn.com>,
        Paul Moore <paul@paul-moore.com>,
        Stephen Smalley <sds@tycho.nsa.gov>,
        Eric Paris <eparis@parisplace.org>,
        James Morris <james.l.morris
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On 10/21/2017 6:45 AM, Nicolas Belouin wrote:
> with CAP_SYS_ADMIN being bloated, the usefulness of using it to
> flag a process to be entrusted for e.g reading and writing trusted
> xattr is near zero.
> CAP_TRUSTED aims to provide userland with a way to mark a process as
> entrusted to do specific (not specially admin-centered) actions. It
> would for example allow a process to red/write the trusted xattrs.

Please explain how this is different from CAP_MAC_ADMIN in
any existing use case. If it is significantly different, how
would the two interact?

> Signed-off-by: Nicolas Belouin <nicolas@belouin.fr>
> ---
>  include/uapi/linux/capability.h     | 6 +++++-
>  security/selinux/include/classmap.h | 5 +++--
>  2 files changed, 8 insertions(+), 3 deletions(-)
>
> diff --git a/include/uapi/linux/capability.h b/include/uapi/linux/capability.h
> index ce230aa6d928..27e457b93c84 100644
> --- a/include/uapi/linux/capability.h
> +++ b/include/uapi/linux/capability.h
> @@ -369,7 +369,11 @@ struct vfs_ns_cap_data {
>  
>  #define CAP_SYS_MOUNT		38
>  
> -#define CAP_LAST_CAP         CAP_SYS_MOUNT
> +/* Allow read/write trusted xattr */
> +
> +#define CAP_TRUSTED		39
> +
> +#define CAP_LAST_CAP         CAP_TRUSTED
>  
>  #define cap_valid(x) ((x) >= 0 && (x) <= CAP_LAST_CAP)
>  
> diff --git a/security/selinux/include/classmap.h b/security/selinux/include/classmap.h
> index a873dce97fd5..f5dc8e109f5a 100644
> --- a/security/selinux/include/classmap.h
> +++ b/security/selinux/include/classmap.h
> @@ -24,9 +24,10 @@
>  	    "audit_control", "setfcap"
>  
>  #define COMMON_CAP2_PERMS  "mac_override", "mac_admin", "syslog", \
> -		"wake_alarm", "block_suspend", "audit_read", "sys_mount"
> +		"wake_alarm", "block_suspend", "audit_read", "sys_mount", \
> +		"trusted"
>  
> -#if CAP_LAST_CAP > CAP_SYS_MOUNT
> +#if CAP_LAST_CAP > CAP_TRUSTED
>  #error New capability defined, please update COMMON_CAP2_PERMS.
>  #endif
>