Re: [PATCH v7 6/6] evm: Support multiple LSMs providing an xattr

[Mimi Zohar]

On Mon, 2023-02-20 at 10:49 +0100, Roberto Sassu wrote:
> On Sun, 2023-02-19 at 14:42 -0500, Mimi Zohar wrote:
> > On Thu, 2022-12-01 at 11:41 +0100, Roberto Sassu wrote:
> > > From: Roberto Sassu <roberto.sassu@xxxxxxxxxx>
> > > 
> > > Currently, evm_inode_init_security() processes a single LSM xattr from
> > > the array passed by security_inode_init_security(), and calculates the
> > > HMAC on it and other inode metadata.
> > > 
> > > Given that initxattrs() callbacks, called by
> > > security_inode_init_security(), expect that this array is terminated when
> > > the xattr name is set to NULL, reuse the same assumption to scan all xattrs
> > > and to calculate the HMAC on all of them.
> > > 
> > > Signed-off-by: Roberto Sassu <roberto.sassu@xxxxxxxxxx>
> > > Reviewed-by: Casey Schaufler <casey@xxxxxxxxxxxxxxxx>
> > 
> > Normally changing the contents of the EVM HMAC calculation would break
> > existing systems.  Assuming for the time being this is safe, at what
> > point will it affect backwards compatability?  Should it be documented
> > now or then?
> 
> Actually, the current patch set continues to fullfill user space
> expectation on the EVM behavior. If the LSM infrastructure created more
> xattrs and EVM calculated the HMAC on just one, there would be a
> problem on subsequent xattr operations and on IMA verification.
> 
> By updating both the LSM infrastructure and EVM to support multiple
> xattrs, everything will continue to work.

Agreed.  Thank you for the reminder of the bug report being addressed
by this patch set.

Reviewed-by: Mimi Zohar <zohar@xxxxxxxxxxxxx>

-- 
thanks,

Mimi