linux-kernel - Re: [RFC 2/2] ima: Fix detection of read/write violations on stacked filesystems

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Date: Tue, 16 Apr 2024 15:05:49 -0400
From: Mimi Zohar <zohar@...ux.ibm.com>
To: Miklos Szeredi <miklos@...redi.hu>
Cc: Stefan Berger <stefanb@...ux.ibm.com>,
        Amir Goldstein
 <amir73il@...il.com>, linux-integrity@...r.kernel.org,
        linux-unionfs@...r.kernel.org, linux-kernel@...r.kernel.org,
        roberto.sassu@...wei.com, Christian Brauner <brauner@...nel.org>
Subject: Re: [RFC 2/2] ima: Fix detection of read/write violations on
 stacked filesystems

On Tue, 2024-04-16 at 16:46 +0200, Miklos Szeredi wrote:
> On Tue, 16 Apr 2024 at 14:18, Mimi Zohar <zohar@...ux.ibm.com> wrote:
> > Originally there was a single measureent unless the filesystem was mounted with
> > SB_I_VERSION.  With commit a2a2c3c8580a ("ima: Use i_version only when
> > filesystem supports it") this changed to always re-measure the file if the
> > filesystem wasn't mounted with SB_I_VERSION.
> 
> Does the i_version get stored and compared only while the inode is in memory?
> 
> In that case I think it should be possible to support a version number
> for the overlay inode.

i_version was insufficient to detect a file change for overlay.  Commit
b836c4d29f27 ("ima: detect changes to the backing overlay") also compares the
i_ino and s_dev as well.  Refer to 
https://lore.kernel.org/lkml/20231025143906.133218-1-zohar@linux.ibm.com/.

Here in this patch set we need to detect IMA read/write violations, based on the
i_readcount/i_writecount.  If an overlay file is opened for read, but the
backing file is already opened for write, the file measurement is
meaningless.  An "open-writers" violation needs to be generated; and the IMA
measurement list needs to be invalidated.

thanks,

Mimi