linux-kernel - Re: [PATCH 3/7] ima: Introduce template fields mntuidmap and mntgidmap

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Message-ID: <20210520094105.x2k3bc53xejfl5b2@wittgenstein>
Date:   Thu, 20 May 2021 11:41:05 +0200
From:   Christian Brauner <christian.brauner@...ntu.com>
To:     Roberto Sassu <roberto.sassu@...wei.com>
Cc:     zohar@...ux.ibm.com, mjg59@...f.ucam.org,
        linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/7] ima: Introduce template fields mntuidmap and
 mntgidmap

On Thu, May 20, 2021 at 11:37:07AM +0200, Christian Brauner wrote:
> On Thu, May 20, 2021 at 10:56:57AM +0200, Roberto Sassu wrote:
> > This patch introduces the new template fields mntuidmap and mntgidmap,
> > which include respectively the UID and GID mappings of the idmapped mount,
> > if the user namespace is not the initial one.
> > 
> > These template fields, which should be included whenever the iuid and the
> > igid fields are included, allow remote verifiers to find the original UID
> > and GID of the inode during signature verification. The iuid and igid
> > fields include the mapped UID and GID when the inode is in an idmapped
> > mount.
> > 
> > This solution has been preferred to providing always the original UID and
> > GID, regardless of whether the inode is in an idmapped mount or not, as
> > the mapped UID and GID are those seen by processes and matched with the IMA
> > policy.
> 
> Hm, looking at the code this doesn't seem like a good idea to me. I
> think we should avoid that and just rely on the original uid and gid.

It'd be ok to include the mapped uid/gid but don't copy the mapping
itself.