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

Greg KH
2022-12-09T08:46:19Z

On Fri, Dec 09, 2022 at 03:53:25PM +0800, Guozihua (Scott) wrote:
> 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.

Ok, so it's much more than just 4.19 that's an issue here. And are
those commits tagged for stable inclusion?

> 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.

Ok, then provide a series of backports to 4.19 and we will be glad to
review them.

thanks,

greg k-h