From: Mimi Zohar <zohar@linux.ibm.com>
To: Miklos Szeredi <miklos@szeredi.hu>
Cc: Stefan Berger <stefanb@linux.ibm.com>,
Amir Goldstein <amir73il@gmail.com>,
linux-integrity@vger.kernel.org, linux-unionfs@vger.kernel.org,
linux-kernel@vger.kernel.org, roberto.sassu@huawei.com,
Christian Brauner <brauner@kernel.org>
Subject: Re: [RFC 2/2] ima: Fix detection of read/write violations on stacked filesystems
Date: Wed, 01 May 2024 17:13:25 -0400 [thread overview]
Message-ID: <e1d868f3612f2e3480e84d6489a78337a68cb748.camel@linux.ibm.com> (raw)
In-Reply-To: <CAJfpegtH8z3uRcSPCQ_3kj-XoV9rUnJc5nE+CQSrCuBMajEmeQ@mail.gmail.com>
On Tue, 2024-04-23 at 13:06 +0200, Miklos Szeredi wrote:
> On Tue, 16 Apr 2024 at 21:06, Mimi Zohar <zohar@linux.ibm.com> wrote:
> > On Tue, 2024-04-16 at 16:46 +0200, Miklos Szeredi wrote:
> > > On Tue, 16 Apr 2024 at 14:18, Mimi Zohar <zohar@linux.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/.
>
> Which is rather ad-hoc.
>
> I'm talking about returning something in overlay i_version, which
> really indicates the version of the overlay file calculated from the
> i_version of the underlying files. The only issue is making this
> i_version persistent, AFAICS. If that's not needed than the overlayfs
> specific logic in IMA could be moved into overlayfs, where it belongs.
IMA saves the i_version in order to detect whether or not the file has changed.
between one access and another. The i_version value, itself, does not need to be
persistent but needs to be consistent.
>
> > 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.
>
> If there's no other way, then let's implement an API to query the
> writecount that can take overlayfs into account. This is for the VFS
> and/or overlayfs to calculate, not for IMA.
Thanks, that will definitely simplify IMA.
Mimi
prev parent reply other threads:[~2024-05-01 21:13 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-12 14:01 [RFC 0/2] ima: Fix detection of read/write violations on stacked filesystems Stefan Berger
2024-04-12 14:01 ` [RFC 1/2] ovl: Define D_REAL_FILEDATA for d_real to return dentry with data Stefan Berger
2024-04-12 18:05 ` Amir Goldstein
2024-04-12 14:01 ` [RFC 2/2] ima: Fix detection of read/write violations on stacked filesystems Stefan Berger
2024-04-12 18:08 ` Amir Goldstein
2024-04-12 19:08 ` Stefan Berger
2024-04-15 8:09 ` Miklos Szeredi
2024-04-15 10:47 ` Mimi Zohar
2024-04-15 12:57 ` Miklos Szeredi
2024-04-15 18:34 ` Mimi Zohar
2024-04-16 8:05 ` Miklos Szeredi
2024-04-16 12:18 ` Mimi Zohar
2024-04-16 14:46 ` Miklos Szeredi
2024-04-16 19:05 ` Mimi Zohar
2024-04-23 11:06 ` Miklos Szeredi
2024-05-01 21:13 ` Mimi Zohar [this message]
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