linux-kernel - Re: [RFC 15/20] capabilities: Introduce CAP_INTEGRITY

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Date:   Tue, 30 Nov 2021 09:27:30 -0800
From:   Casey Schaufler <casey@...aufler-ca.com>
To:     Stefan Berger <stefanb@...ux.ibm.com>,
        linux-integrity@...r.kernel.org
Cc:     zohar@...ux.ibm.com, serge@...lyn.com,
        christian.brauner@...ntu.com, containers@...ts.linux.dev,
        dmitry.kasatkin@...il.com, ebiederm@...ssion.com,
        krzysztof.struczynski@...wei.com, roberto.sassu@...wei.com,
        mpeters@...hat.com, lhinds@...hat.com, lsturman@...hat.com,
        puiterwi@...hat.com, jejb@...ux.ibm.com, jamjoom@...ibm.com,
        linux-kernel@...r.kernel.org, paul@...l-moore.com, rgb@...hat.com,
        linux-security-module@...r.kernel.org, jmorris@...ei.org,
        Denis Semakin <denis.semakin@...wei.com>,
        Casey Schaufler <casey@...aufler-ca.com>
Subject: Re: [RFC 15/20] capabilities: Introduce CAP_INTEGRITY_ADMIN

On 11/30/2021 8:06 AM, Stefan Berger wrote:
> From: Denis Semakin <denis.semakin@...wei.com>
>
> This patch introduces CAP_INTEGRITY_ADMIN, a new capability that allows
> to setup IMA (Integrity Measurement Architecture) policies per container
> for non-root users.

Why not use CAP_MAC_ADMIN? IMA is a mandatory policy. The scope
is system security administration. It seems to fit your needs.
I introduced CAP_MAC_ADMIN for Smack, and believe that IMA using
it would be completely appropriate.

>
> The main purpose of this new capability is discribed in this document:
> https://kernsec.org/wiki/index.php/IMA_Namespacing_design_considerations
> It is said: "setting the policy should be possibly without the powerful
> CAP_SYS_ADMIN and there should be the opportunity to gate this with a new
> capability CAP_INTEGRITY_ADMIN that allows a user to set the IMA policy
> during container runtime.."
>
> In other words it should be possible to setup IMA policies while not
> giving too many privilges to the user, therefore splitting the
> CAP_INTEGRITY_ADMIN off from CAP_SYS_ADMIN.
>
> Signed-off-by: Denis Semakin <denis.semakin@...wei.com>
> Signed-off-by: Stefan Berger <stefanb@...ux.ibm.com>
> ---
>   include/linux/capability.h          | 6 ++++++
>   include/uapi/linux/capability.h     | 7 ++++++-
>   security/selinux/include/classmap.h | 4 ++--
>   3 files changed, 14 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/capability.h b/include/linux/capability.h
> index 65efb74c3585..ea6d58acb95e 100644
> --- a/include/linux/capability.h
> +++ b/include/linux/capability.h
> @@ -278,4 +278,10 @@ int get_vfs_caps_from_disk(struct user_namespace *mnt_userns,
>   int cap_convert_nscap(struct user_namespace *mnt_userns, struct dentry *dentry,
>   		      const void **ivalue, size_t size);
>   
> +static inline bool integrity_admin_ns_capable(struct user_namespace *ns)
> +{
> +	return ns_capable(ns, CAP_INTEGRITY_ADMIN) ||
> +		ns_capable(ns, CAP_SYS_ADMIN);
> +}
> +
>   #endif /* !_LINUX_CAPABILITY_H */
> diff --git a/include/uapi/linux/capability.h b/include/uapi/linux/capability.h
> index 463d1ba2232a..48b08e4b3895 100644
> --- a/include/uapi/linux/capability.h
> +++ b/include/uapi/linux/capability.h
> @@ -417,7 +417,12 @@ struct vfs_ns_cap_data {
>   
>   #define CAP_CHECKPOINT_RESTORE	40
>   
> -#define CAP_LAST_CAP         CAP_CHECKPOINT_RESTORE
> +/* Allow setup IMA policy per container independently */
> +/* No necessary to be superuser */
> +
> +#define CAP_INTEGRITY_ADMIN	41
> +
> +#define CAP_LAST_CAP		CAP_INTEGRITY_ADMIN
>   
>   #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 35aac62a662e..7ff532b90f09 100644
> --- a/security/selinux/include/classmap.h
> +++ b/security/selinux/include/classmap.h
> @@ -28,9 +28,9 @@
>   
>   #define COMMON_CAP2_PERMS  "mac_override", "mac_admin", "syslog", \
>   		"wake_alarm", "block_suspend", "audit_read", "perfmon", "bpf", \
> -		"checkpoint_restore"
> +		"checkpoint_restore", "integrity_admin"
>   
> -#if CAP_LAST_CAP > CAP_CHECKPOINT_RESTORE
> +#if CAP_LAST_CAP > CAP_INTEGRITY_ADMIN
>   #error New capability defined, please update COMMON_CAP2_PERMS.
>   #endif
>