Re: [RFC] IMA LSM based rule race condition issue on 4.19 LTS

["Guozihua (Scott)" <guozihua@huawei.com>]

On 2022/12/9 15:12, Greg KH wrote:
> On Fri, Dec 09, 2022 at 03:00:35PM +0800, Guozihua (Scott) wrote:
>> Hi community.
>>
>> Previously our team reported a race condition in IMA relates to LSM based
>> rules which would case IMA to match files that should be filtered out under
>> normal condition. The issue was originally analyzed and fixed on mainstream.
>> The patch and the discussion could be found here:
>> https://lore.kernel.org/all/20220921125804.59490-1-guozihua@huawei.com/
>>
>> After that, we did a regression test on 4.19 LTS and the same issue arises.
>> Further analysis reveled that the issue is from a completely different
>> cause.
> 
> What commit in the tree fixed this in newer kernels?  Why can't we just
> backport that one to 4.19.y as well?
> 
> thanks,
> 
> greg k-h

Hi Greg,

The fix for mainline is now on linux-next, commit 	d57378d3aa4d ("ima: 
Simplify ima_lsm_copy_rule") and 	c7423dbdbc9ece ("ima: Handle -ESTALE 
returned by ima_filter_rule_match()"). However, these patches cannot be 
picked directly into 4.19.y due to code difference.

The commit which introduced the issue on mainline was believed to be 
b16942455193 ("ima: use the lsm policy update notifier"), which is not 
in 4.19.y. And the mainline patch is designed to handle the situation 
when IMA rules are accessed through RCU which has not been implemented 
on 4.19.y either.

-- 
Best
GUO Zihua