Re: [PATCH 2/2] ima: Call ima_calc_boot_aggregate() in ima_eventdigest_init()

[Mimi Zohar <zohar@linux.ibm.com>]

On Thu, 2020-06-04 at 16:12 -0300, Bruno Meneguele wrote:
> On Wed, Jun 03, 2020 at 06:03:35PM -0400, Mimi Zohar wrote:
> > Hi Roberto,
> > 
> > On Wed, 2020-06-03 at 17:08 +0200, Roberto Sassu wrote:
> > > If the template field 'd' is chosen and the digest to be added to the
> > > measurement entry was not calculated with SHA1 or MD5, it is
> > > recalculated with SHA1, by using the passed file descriptor. However, this
> > > cannot be done for boot_aggregate, because there is no file descriptor.
> > > 
> > > This patch adds a call to ima_calc_boot_aggregate() in
> > > ima_eventdigest_init(), so that the digest can be recalculated also for the
> > > boot_aggregate entry.
> > > 
> > > Cc: stable@vger.kernel.org # 3.13.x
> > > Fixes: 3ce1217d6cd5d ("ima: define template fields library and new helpers")
> > > Reported-by: Takashi Iwai <tiwai@suse.de>
> > > Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
> > 
> > Thanks, Roberto.
> > 
> > I've pushed both patches out to the next-integrity branch and would
> > appreciate some additional testing.
> > 
> > thanks,
> > 
> > Mimi
> > 
> 
> Hi Mimi and Roberto,
> 
> FWIW, I've tested this patch manually and things went fine, with no
> unexpected behavior or results. 

Thanks, Bruno!

> However, wouldn't it be worth add a note in kmsg about the
> ima_calc_boot_aggregate() being called with an algo different from the
> system's default? Just to let the user know he won't find a sha256 when
> check the measurement. But that's something we can add later too.

There's no guarantees that the IMA default crypto algorithm will be
used for calculating the boot_aggregate.  The algorithm is dependent
on the TPM.  For example, the default IMA algorithm could be sha256,
but on a system with TPM 1.2, the boot_aggregate would have to be
sha1.

This patch addresses a mismatch between the template format field ('d'
field) and the larger digest.  We could require the "ima_template_fmt"
specified on the boot command line define an appropriate format, but
Roberto decided to support the situation where both "d" and "d-ng" are
defined.

Mimi