Re: [PATCH v14 6/6] LSM: Multiple LSM Documentation and cleanup

From: Randy Dunlap
Date: Fri Jul 26 2013 - 19:18:17 EST

On 07/25/13 11:32, Casey Schaufler wrote:
> Subject: [PATCH v14 6/6] LSM: Multiple LSM Documentation and cleanup
> Add documentation and remove the obsolete capability LSM.
> Clean up some comments in security.h
> Signed-off-by: Casey Schaufler <casey@xxxxxxxxxxxxxxxx>
> ---
> Documentation/security/LSM.txt | 56 +-
> include/linux/security.h | 48 +-
> security/Makefile | 1 -
> security/capability.c | 1106 ----------------------------------------
> 4 files changed, 77 insertions(+), 1134 deletions(-)
> diff --git a/Documentation/security/LSM.txt b/Documentation/security/LSM.txt
> index c335a76..69cf466 100644
> --- a/Documentation/security/LSM.txt
> +++ b/Documentation/security/LSM.txt
> @@ -7,20 +7,56 @@ various security checks to be hooked by new kernel extensions. The name
> loadable kernel modules. Instead, they are selectable at build-time via
> CONFIG_DEFAULT_SECURITY and can be overridden at boot-time via the
> "security=..." kernel command line argument, in the case where multiple
> -LSMs were built into a given kernel.
> +LSMs were built into a given kernel. The names of the active LSMs
> +can be read from /sys/kernel/security/lsm.
> +
> +Both CONFIG_DEFAULT_SECURITY and the "security=" option take a comma
> +separated list of LSM names. The LSM hooks are invoked in the order
> +specified. All hooks provided are invoked regardless of the outcome
> +of preceding hooks. Hooks that return success or failure results
> +return success if all of the LSM provided hooks succeed and the error
> +code of the last failing hook on error.
> +
> +Information from an LSM can come in one of two forms. The raw data
> +used by the LSM is typically the preferred form. SELinux contexts and
> +Smack labels are examples of raw LSM data. If the data from multiple
> +LSMs is presented together it will be in the form:
> +
> + lsmname='value'[lsmname='value']...

no commas? just (made up example):


> +
> +Interfaces that accept LSM data as input accept this format as well,
> +passing only the relevant portion of the data to each LSM.
> +
> +The /proc filesystem attribute interface supports files from a time
> +when only one LSM could be used at a time. CONFIG_PRESENT_SECURITY
> +defines which LSM uses these interfaces. The name of this LSM can be
> +read from /sys/kernel/security/present. There are also LSM identified
> +interfaces which should be used in preference to the undifferentiated
> +interfaces. The attribute interface "context" always provides the
> +data from all LSMs that maintain it in the lsmname='value' format.
> +
> +The three networking mechanisms supporting LSM attributes are
> +restricted to providing those attributes for a single LSM each.
> +CONFIG_SECMARK_LSM specifies which LSM will provide hooks for the
> +secmark mechanism. CONFIG_NETLABEL_LSM specifies which LSM hooks
> +are used by NetLabel to provide IPv4 CIPSO headers. CONFIG_XFRM_LSM
> +specifies the LSM providing xfrm hooks. CONFIG_PEERSEC_LSM allows
> +for either a specific LSM to provide data with SO_PEERSEC or for
> +all LSMs that provide data to do so.
> +
> +The Linux capabilities system is used in conjunction with any LSMs.
> +LSM hooks are called after the capability checks in most cases,
> +but after in a small number of cases. All LSM hooks need to be aware

one of these 'after's should be 'before' ??

> +of the potential interactions with the capability system. For more
> +details on capabilities, see capabilities(7) in the Linux man-pages
> +project.
> The primary users of the LSM interface are Mandatory Access Control
> (MAC) extensions which provide a comprehensive security policy. Examples
> include SELinux, Smack, Tomoyo, and AppArmor. In addition to the larger
> -MAC extensions, other extensions can be built using the LSM to provide
> -specific changes to system operation when these tweaks are not available
> -in the core functionality of Linux itself.
> -
> -Without a specific LSM built into the kernel, the default LSM will be the
> -Linux capabilities system. Most LSMs choose to extend the capabilities
> -system, building their checks on top of the defined capability hooks.
> -For more details on capabilities, see capabilities(7) in the Linux
> -man-pages project.
> +MAC extensions, other extensions such as Yama can be built using the LSM
> +to provide specific changes to system operation when these tweaks are not
> +available in the core functionality of Linux itself.
> Based on,
> a new LSM is accepted into the kernel when its intent (a description of

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