linux-kernel - Re: [PATCH 2/4] AppArmor: Fix security_task

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Message-ID: <4C7BE205.40202@canonical.com>
Date:	Mon, 30 Aug 2010 09:53:25 -0700
From:	John Johansen <john.johansen@...onical.com>
To:	Jiri Slaby <jirislaby@...il.com>
CC:	linux-kernel@...r.kernel.org, linux-security-module@...r.kernel.org
Subject: Re: [PATCH 2/4] AppArmor: Fix security_task_setrlimit logic for 2.6.36
 changes

On 08/28/2010 01:48 PM, Jiri Slaby wrote:
> On 08/28/2010 10:35 PM, John Johansen wrote:
>> On 08/28/2010 11:15 AM, Jiri Slaby wrote:
>>> On 08/28/2010 07:10 PM, John Johansen wrote:
>>>> 2.6.36 introduced the abilitiy to specify the task that is having its
>>>> rlimits set.  Update mediation to ensure that confined tasks can only
>>>> set their own group_leader as expected by current policy.
>>>>
>>>> Add TODO note about extending policy to support setting other tasks
>>>> rlimits.
>>> ...
>>>> --- a/security/apparmor/resource.c
>>>> +++ b/security/apparmor/resource.c
>>> ...
>>>> @@ -79,18 +80,21 @@ int aa_map_resource(int resource)
>>>>   *
>>>>   * Returns: 0 or error code if setting resource failed
>>>>   */
>>>> -int aa_task_setrlimit(struct aa_profile *profile, unsigned int resource,
>>>> -		      struct rlimit *new_rlim)
>>>> +int aa_task_setrlimit(struct aa_profile *profile, struct task_struct *task,
>>>> +		      unsigned int resource, struct rlimit *new_rlim)
>>>>  {
>>>>  	int error = 0;
>>>>  
>>>> -	if (profile->rlimits.mask & (1 << resource) &&
>>>> -	    new_rlim->rlim_max > profile->rlimits.limits[resource].rlim_max)
>>>> -
>>>> -		error = audit_resource(profile, resource, new_rlim->rlim_max,
>>>> -			-EACCES);
>>>> +	/* TODO: extend resource control to handle non group leader tasks.
>>>> +	 * AppArmor rules currently have the implicit assumption that
>>>> +	 * the task having its resource set is the group leader.
>>>
>>> Why would you want to do that? Limits are per process, so the 'task'
>>> parameter is guaranteed to be the leader.
>>>
>> That used to be the case,
> 
> It is still the case. The limits (the same as signals or accounting) are
> per-process, they are not per-thread. If you look into do_prlimit() how
> security_task_setrlimit() is called, you'll see.
>
>> commit c022a0acad534fd5f5d5f17280f6d4d135e74e81 add the prlimit64 syscall
>> which
>>
>>     It also adds a possibility of changing limits of other processes. We
>>     check the user's permissions to do that and if it succeeds, the new
>>     limits are propagated online.
> ...
>> so it seems we need to extend the apparmor rules to be able to deal with
>> this, but ensuring that the current assumption is enforced is enough
>> for now.
> 
> Yeah, I remember, the other Jiri inside wrote that. You are guaranteed
> to get the group leader right now. And if it ever changes, which is
> unlikely, all users would have to be checked and fixed anyway.
> 
Right, it is the same.  I wrote the comment after verifying that only the
group leader was being set, and for some reason I ended up substituting
group leader for process when writing the comment, which really make the
it confusing and wrong.

It should have been more along the lines of

/* TODO: extend resource control to handle other (non current) processes.
 * AppArmor rules currently have the implicit assumption that the task
 * is setting the resource of the current process
 */

I'll update asap

thanks Jiri
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