linux-kernel - Re: [PATCH v3] ima: detect changes to the backing overlay file

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Message-ID: <CAHQZ30BbtoTGHV803WpiSdCi6Bz9E050FJUy=HEeSAti_zPsqg@mail.gmail.com>
Date:   Thu, 26 Oct 2023 09:31:42 -0600
From:   Raul Rangel <rrangel@...omium.org>
To:     Mimi Zohar <zohar@...ux.ibm.com>
Cc:     Eric Snowberg <eric.snowberg@...cle.com>,
        "linux-integrity@...r.kernel.org" <linux-integrity@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        Amir Goldstein <amir73il@...il.com>
Subject: Re: [PATCH v3] ima: detect changes to the backing overlay file

On Wed, Oct 25, 2023 at 12:01 PM Mimi Zohar <zohar@...ux.ibm.com> wrote:
>
> On Wed, 2023-10-25 at 16:27 +0000, Eric Snowberg wrote:
> >
> > > On Oct 25, 2023, at 8:39 AM, Mimi Zohar <zohar@...ux.ibm.com> wrote:
> > >
> > > Commit 18b44bc5a672 ("ovl: Always reevaluate the file signature for
> > > IMA") forced signature re-evaulation on every file access.
> > >
> > > Instead of always re-evaluating the file's integrity, detect a change
> > > to the backing file, by comparing the cached file metadata with the
> > > backing file's metadata.  Verifying just the i_version has not changed
> > > is insufficient.  In addition save and compare the i_ino and s_dev
> > > as well.
> > >
> > > Signed-off-by: Mimi Zohar <zohar@...ux.ibm.com>
> >
> > I ran the file integrity tests that originally uncovered the need for
> > "Commit 18b44bc5a672 ("ovl: Always reevaluate the file signature for
> > IMA”). When the backing file is changed, file integrity remains.  For that
> > part, feel free to add:
> >
> > Tested-by: Eric Snowberg <eric.snowberg@...cle.com>
>
> Thanks!
>
> Mimi
>

I just verified this fixes the speed regression:

```
rrangel920 / # time clang --version >/dev/null

real 0m0.369s
user 0m0.000s
sys 0m0.368s
rrangel920 / #
rrangel920 / # time clang --version >/dev/null

real 0m0.017s
user 0m0.004s
sys 0m0.013s
rrangel920 / # time clang --version >/dev/null

real 0m0.012s
user 0m0.000s
sys 0m0.012s
rrangel920 / # time clang --version >/dev/null

real 0m0.012s
user 0m0.000s
sys 0m0.012s
```

Tested-by: Raul E Rangel <rrangel@...omium.org>

Thanks again for the quick fix!