Re: [RESEND][PATCH] Documentation: added order requirement for ima_hash=

[Guozihua (Scott)]

On 2022/1/26 12:37, Mimi Zohar wrote:
> On Wed, 2022-01-26 at 10:28 +0800, Guozihua (Scott) wrote:
> > On 2022/1/26 9:07, Mimi Zohar wrote:
> > > On Tue, 2022-01-25 at 17:02 +0800, GUO Zihua wrote:
> > > > From: Guo Zihua <guozihua@xxxxxxxxxx>
> > > >
> > > > Commandline parameter ima_hash= and ima_template= has order requirement
> > > > for them to work correctly together. Namely ima_hash= must be
> > > > specified after ima_template=, otherwise ima_template= will be ignored.
> > > >
> > > > The reason is that when handling ima_hash=, ima template would be set to
> > > > the default value if it has not been initialized already, and that value
> > > > cannot be changed afterwards by ima_template=.
> > > >
> > > > This patch adds this limitation to the documentation.
> > > >
> > > > Reviewed-by: Roberto Sassu <roberto.sassu@xxxxxxxxxx>
> > > > Signed-off-by: Guo Zihua <guozihua@xxxxxxxxxx>
> > >
> > > This issue should be limited to the original "ima" template format,
> > > which only supports hash algorithms of 20 bytes or less.  The "ima_ng"
> > > template has been the default since larger digests and templates were
> > > upstreamed back in Linux 3.13[1]. Do you really still have kernels
> > > built with the original "ima" template?
> > >
> > > [1] Refer to commit 4286587dccd4 ("ima: add Kconfig default measurement
> > > list template").
> >
> > Hi Mimi,
> >
> > The issue is that if ima_hash is specified before ima_template,
> > ima_template will not work. Built-in default only affects which template
> > will be loaded eventually.
> >
> > For example, if the built-in default template is ima-ng and user would
> > like to change it to ima-sig with sha512 by specifying "ima_hash=sha512
> > ima_template=ima-sig" in command line, the result will be ima-ng with
> > sha512, not ima-sig with sha512.
>
> Ok.  Once the template name is set, ima_template_setup() doesn't allow
> it to be reset.  This was probably done to set the template name to the
> first occurance of "ima_template=" on the boot command line.  This
> concern could be addressed by defining a static local variable in
> ima_template_setup().
>
> So either documenting the ordering requirement, as you've done, or
> allowing the template_name to be reset are fine.
>
> thanks,
>
> Mimi
>
> .

The main issue lies in ima_template_desc_current called by hash_setup, 
which does not just read ima_template global variable, but also tries to 
set it if that hasn't been done already. Causing ima_template_setup to quit.

--
Best
GUO Zihua