lkml.org 
[lkml]   [2012]   [Dec]   [11]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: [PATCH 0/2] ima: policy search speedup
From
On Tue, Dec 11, 2012 at 8:09 PM, Eric Paris <eparis@parisplace.org> wrote:
> On Tue, Dec 11, 2012 at 12:55 PM, Linus Torvalds
> <torvalds@linux-foundation.org> wrote:
>
>> And your "pseudo-filesystems" argument is pretty stupid too, since WE
>> ALREADY HAVE A FLAG FOR THAT!
>>
>> Guess where it is? Oh, it's in the place I already mentioned makes
>> more sense. Look for S_PRIVATE in inode->i_flags, and IS_PRIVATE() in
>> users. It's what the other security models already use to avoid
>> bothering calling down to the security layers. The fact that the
>> integrity layer bypasses the normal security layer in
>> ima_file_check(), for example, is no excuse to then make up totally
>> new flags.
>
> IS_PRIVATE() is not used by and darn well better not be used by, all
> psuedo filesystems like procfs which IMA may want to ignore. LSMs
> like to do control on them. I thought S_PRIVATE was really only used
> by the anon_inode and reiserfs's really crazy ass internal inodes. I
> could always be wrong.
>
> I don't know if I agree with dmitry but let me explain what's going on here.
>
> Lets say the user accesses an inode in procfs. Without this patch one
> would search the ima policy and find a rule that says 'if this inode
> is on procfs we don't care.' We can then cache that in the struct
> inode like you say and move along. If another inode on procfs is
> opened we will have the same policy search and the same per inode 'i
> don't give a crap' marking. This absolutely works you are right. But
> we search the IMA policy for every inode.
>
> With Dmitry's patch we can instead search the IMA policy one time and
> mark the whole superblock as 'i don't give a crap' if IMA policy says
> we don't care about that fstype. When the second procfs inode is
> opened we instead look at the per superblock 'who gives a crap' and
> never search the IMA policy. So we save all future policy searches.
>
> I'd say this patch would only be a good idea if there is a real
> performance hit which is measurable in a real work situation. Not,
> 'look how much faster it is to access proc inodes' microbenchmark,
> since noone is actually going to do that, but some results of a useful
> benchmark you care about. Maybe Dmitry gave those numbers and I
> missed them? Otherwise, stick with per inode like Linus wants...

I was measuring that during on the system without super block flag,
policy search was happening 100 000 times, but with the flag just bellow 10 000.
For desktop multi-core systems powered from the plug it might be unnoticeable.
But for the handhald it might save the battery.

- Dmitry


\
 
 \ /
  Last update: 2012-12-11 20:01    [W:0.153 / U:0.060 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site