linux-kernel - Re: [PATCH 1/3] IMA: move read/write counters into struct inode

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Message-ID: <4CC06721.8020308@schaufler-ca.com>
Date:	Thu, 21 Oct 2010 09:15:29 -0700
From:	Casey Schaufler <casey@...aufler-ca.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Eric Paris <eparis@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, hch@...radead.org, zohar@...ibm.com,
	warthog9@...nel.org, david@...morbit.com, jmorris@...ei.org,
	kyle@...artin.ca, hpa@...or.com, akpm@...ux-foundation.org
Subject: Re: [PATCH 1/3] IMA: move read/write counters into struct inode

 On 10/20/2010 8:15 AM, Ingo Molnar wrote:
> * Eric Paris <eparis@...hat.com> wrote:
>
>> On Wed, 2010-10-20 at 16:38 +0200, Ingo Molnar wrote:
>>> * Eric Paris <eparis@...hat.com> wrote:
>>>
>>>> Executive summary of the day's work:
>>>> Yesterday morning: 944 bytes per inode in core
>>>> Yesterday night: 24 bytes per inode in core
>>>> Tonight: 4 bytes per inode in core.
>>>>
>>>> That's a x236 time reduction in memory usage.  No I didn't even start looking 
>>>> at a freezer.  Which could bring that 4 down to 0, but would add a scalability 
>>>> penalty on all inodes when IMA was enabled.
>>> Why not use inode->i_security intelligently? That already exists so that way 
>>> it's 0 bytes.
>>>
>>> Thanks,
>> It still wouldn't be 0 bytes since there would be a 1-1 mapping from inode to 
>> i_security structs. [...]
> Only for IMA-affected files, right?
>
> My point is to keep it 0 overhead for the _non IMA common case_.
>
>> The real reason I don't pursue this route is because of the litany of different 
>> ways this pointer is used in different LSMs (or not used at all.)  And we all know 
>> that LSM authors aren't known for seeing the world the same way as each other.  As 
>> a maintainer of one of those LSMs even I'm scared to try pushing that forward....
> Ugh. That's a perfect reason to do it exactly like i suggested.

If you would like to make a proposal on LSM stacking other than
the traditional "rip the LSM out" I am sure that everyone in the
IMA, SELinux, TOMOYO, AppArmor and Smack communities would be
happy to have a look. Short of having a viable mechanism for
multiple LSMs to coexist IMA needs its separate space. Yes, people
do use both IMA and LSMs on the same machine at the same time.


> Thanks,
>
> 	Ingo
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