Re: [kernel-hardening] [RFC PATCH 1/2] security, capabilities: create CAP_TRUSTED

[Casey Schaufler <casey@schaufler-ca.com>]

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
>