linux-kernel - Re: [PATCH v5 3/3] ima: Use kstat.ctime as a fallback change detection for stacked fs

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Message-ID: <6f82d5dc6b499ecd03c985d6de20de94fea04cfe.camel@linux.ibm.com>
Date: Wed, 04 Feb 2026 23:26:27 -0500
From: Mimi Zohar <zohar@...ux.ibm.com>
To: Frederick Lawler <fred@...udflare.com>,
        Roberto Sassu
	 <roberto.sassu@...weicloud.com>
Cc: Roberto Sassu <roberto.sassu@...wei.com>,
        Dmitry Kasatkin	
 <dmitry.kasatkin@...il.com>,
        Eric Snowberg <eric.snowberg@...cle.com>,
        Paul
 Moore <paul@...l-moore.com>, James Morris <jmorris@...ei.org>,
        "Serge E.
 Hallyn"	 <serge@...lyn.com>,
        "Darrick J. Wong" <djwong@...nel.org>,
        Christian Brauner	 <brauner@...nel.org>,
        Josef Bacik
 <josef@...icpanda.com>, Jeff Layton	 <jlayton@...nel.org>,
        linux-kernel@...r.kernel.org, linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org, kernel-team@...udflare.com
Subject: Re: [PATCH v5 3/3] ima: Use kstat.ctime as a fallback change
 detection for stacked fs

On Wed, 2026-02-04 at 15:22 -0600, Frederick Lawler wrote:
> That said, I think Mimi pointed out in an email [2] where multi-grain
> file systems are impacted regardless of stacked fs or not due to the last
> writer check.
> 
> I don't recall coming across that in my tests, but perhaps I did that
> specific test wrong? To be sure, I created the C program, and on the VM,
> created a XFS disk, mounted it on loopback, ran the rdwr program on
> "somefile" multiple times, and only got 1 audit log for it, until I
> mutated it with touch, and only got 2 hits: original + after mutation
> after running the program multiple times. 
> 
> I'm not sure what's going on there, so I'll look into that a bit more,
> but so far the impact is stacked file systems & multigrain ctime AFAIK.

Make sure you're testing without your patch set applied or at least the last
patch.

Mimi