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

[Christian Brauner]

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.