linux-kernel - Re: [PATCH v22 12/23] LSM: Specify which LSM to display

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Date:   Mon, 9 Nov 2020 14:47:04 -0800
From:   John Johansen <john.johansen@...onical.com>
To:     Casey Schaufler <casey@...aufler-ca.com>,
        Greg KH <gregkh@...uxfoundation.org>
Cc:     casey.schaufler@...el.com, jmorris@...ei.org,
        linux-security-module@...r.kernel.org, selinux@...r.kernel.org,
        linux-audit@...hat.com, keescook@...omium.org,
        penguin-kernel@...ove.sakura.ne.jp, paul@...l-moore.com,
        sds@...ho.nsa.gov, linux-kernel@...r.kernel.org,
        linux-api@...r.kernel.org
Subject: Re: [PATCH v22 12/23] LSM: Specify which LSM to display

On 11/9/20 2:28 PM, Casey Schaufler wrote:
> On 11/7/2020 2:05 PM, John Johansen wrote:
>> On 11/7/20 1:15 AM, Greg KH wrote:
>>> On Fri, Nov 06, 2020 at 04:20:43PM -0800, Casey Schaufler wrote:
>>>> On 11/5/2020 1:22 AM, Greg KH wrote:
>>>>> On Wed, Nov 04, 2020 at 03:41:03PM -0800, Casey Schaufler wrote:
>>>>>> Create a new entry "display" in the procfs attr directory for
>>>>>> controlling which LSM security information is displayed for a
>>>>>> process. A process can only read or write its own display value.
>>>>>>
>>>>>> The name of an active LSM that supplies hooks for
>>>>>> human readable data may be written to "display" to set the
>>>>>> value. The name of the LSM currently in use can be read from
>>>>>> "display". At this point there can only be one LSM capable
>>>>>> of display active. A helper function lsm_task_display() is
>>>>>> provided to get the display slot for a task_struct.
>>>>>>
>>>>>> Setting the "display" requires that all security modules using
>>>>>> setprocattr hooks allow the action. Each security module is
>>>>>> responsible for defining its policy.
>>>>>>
>>>>>> AppArmor hook provided by John Johansen <john.johansen@...onical.com>
>>>>>> SELinux hook provided by Stephen Smalley <sds@...ho.nsa.gov>
>>>>>>
>>>>>> Reviewed-by: Kees Cook <keescook@...omium.org>
>>>>>> Acked-by: Stephen Smalley <sds@...ho.nsa.gov>
>>>>>> Acked-by: Paul Moore <paul@...l-moore.com>
>>>>>> Signed-off-by: Casey Schaufler <casey@...aufler-ca.com>
>>>>>> Cc: linux-api@...r.kernel.org
>>>>>> ---
>>>>>>  fs/proc/base.c                       |   1 +
>>>>>>  include/linux/lsm_hooks.h            |  17 +++
>>>>>>  security/apparmor/include/apparmor.h |   3 +-
>>>>>>  security/apparmor/lsm.c              |  32 +++++
>>>>>>  security/security.c                  | 169 ++++++++++++++++++++++++---
>>>>>>  security/selinux/hooks.c             |  11 ++
>>>>>>  security/selinux/include/classmap.h  |   2 +-
>>>>>>  security/smack/smack_lsm.c           |   7 ++
>>>>>>  8 files changed, 223 insertions(+), 19 deletions(-)
>>>>>>
>>>>>> diff --git a/fs/proc/base.c b/fs/proc/base.c
>>>>>> index 0f707003dda5..7432f24f0132 100644
>>>>>> --- a/fs/proc/base.c
>>>>>> +++ b/fs/proc/base.c
>>>>>> @@ -2806,6 +2806,7 @@ static const struct pid_entry attr_dir_stuff[] = {
>>>>>>  	ATTR(NULL, "fscreate",		0666),
>>>>>>  	ATTR(NULL, "keycreate",		0666),
>>>>>>  	ATTR(NULL, "sockcreate",	0666),
>>>>>> +	ATTR(NULL, "display",		0666),
>>>>> That's a vague name, any chance it can be more descriptive?
>>>> Sure. How about lsm_display, or display_lsm? I wouldn't say that
>>>> any of the files in /proc/*/attr have especially descriptive names,
>>>> but that's hardly an excuse.
>>> I still don't understand what "display" means in this context.  Perhaps
>> its the LSM thats context is being displayed on the shared interface,
>> ie. /proc/*/attr/*
>>
>> thinking about it more owner or even interface_owner might be a better
>> name
> 
> I was hoping for a single word, but I see how something more descriptive
> might be in order. How about "lsm_of_current"? Or "lsm_of_dot_slash_current",
> if you want to be pedantic. "format_of_current" isn't quite accurate, but
> might be easier for some people to understand. Maybe "interface_owning_lsm".
> 
> /proc/*/attr/display answers the question "Which LSM is providing the data
> I see if I look in /proc/*/attr/current, prev or exec or if that process uses
> SO_PEERSEC".
> 

lsm_of_current or interface_lsm or interface_owning_lsm all wfm

> 
>>> documentation will help clear it up?
>>>
>> yeah this needs documented.
> 
> Agreed. I've noticed that nothing in /proc/*/attr seems documented
> in an orderly (documentation/ABI) fashion. I will have to fix some of
> that for a description of /proc/*/attr/whatever_it_ends_up_getting_called
> to make sense. Working on it.
> 
>>> thanks,
>>>
>>> greg k-h
>>>
>