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Date: Mon, 23 Oct 2017 08:57:39 -0400
From: Stephen Smalley <sds@...ho.nsa.gov>
To: Nicolas Belouin <nicolas@...ouin.fr>, David Howells
<dhowells@...hat.com>,
"Theodore Ts'o" <tytso@....edu>,
Andreas Dilger
<adilger.kernel@...ger.ca>,
Alexander Viro <viro@...iv.linux.org.uk>,
Serge
Hallyn <serge@...lyn.com>, Paul Moore <paul@...l-moore.com>,
Eric Paris
<eparis@...isplace.org>,
James Morris <james.l.morris@...cle.com>, linux-cachefs@...hat.com,
linux-kernel@...r.kernel.org, linux-ext4@...r.kernel.org,
linux-fsdevel@...r.kernel.org, linux-security-module@...r.kernel.org,
selinux@...ho.nsa.gov, linux-api@...r.kernel.org,
kernel-hardening@...ts.openwall.com
Subject: Re: [RFC PATCH 1/2] security, capabilities: Add CAP_SYS_MOUNT
On Sat, 2017-10-21 at 15:43 +0200, Nicolas Belouin wrote:
> With CAP_SYS_ADMIN being bloated and inapropriate for actions such
> as mounting/unmounting filesystems, the creation of a new capability
> is needed.
> CAP_SYS_MOUNT is meant to give a process the ability to call for
> mount,
> umount and umount2 syscalls.
If adding a new capability isn't deemed acceptable, then another option
would be to introduce LSM hooks where there isn't already coverage and
implement finer-grained permission checks there. In some cases, that
already occurs for mount and umount*. That also offers the possibility
of taking the object of the operation into account, unlike capabilities
which are only subject/process-based.
>
> Signed-off-by: Nicolas Belouin <nicolas@...ouin.fr>
> ---
> include/uapi/linux/capability.h | 5 ++++-
> security/selinux/include/classmap.h | 4 ++--
> 2 files changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/include/uapi/linux/capability.h
> b/include/uapi/linux/capability.h
> index 230e05d35191..ce230aa6d928 100644
> --- a/include/uapi/linux/capability.h
> +++ b/include/uapi/linux/capability.h
> @@ -365,8 +365,11 @@ struct vfs_ns_cap_data {
>
> #define CAP_AUDIT_READ 37
>
> +/* Allow mounting, unmounting filesystems */
>
> -#define CAP_LAST_CAP CAP_AUDIT_READ
> +#define CAP_SYS_MOUNT 38
> +
> +#define CAP_LAST_CAP CAP_SYS_MOUNT
>
> #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 35ffb29a69cb..a873dce97fd5 100644
> --- a/security/selinux/include/classmap.h
> +++ b/security/selinux/include/classmap.h
> @@ -24,9 +24,9 @@
> "audit_control", "setfcap"
>
> #define COMMON_CAP2_PERMS "mac_override", "mac_admin", "syslog", \
> - "wake_alarm", "block_suspend", "audit_read"
> + "wake_alarm", "block_suspend", "audit_read",
> "sys_mount"
>
> -#if CAP_LAST_CAP > CAP_AUDIT_READ
> +#if CAP_LAST_CAP > CAP_SYS_MOUNT
> #error New capability defined, please update COMMON_CAP2_PERMS.
> #endif
>
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