Re: [PATCH 2/3 v5] add a new template field buf to contain the buffer

[Roberto Sassu]

On 5/18/2019 1:32 AM, prakhar srivastava wrote:
> On Tue, May 14, 2019 at 6:22 AM Roberto Sassu <roberto.sassu@xxxxxxxxxx> wrote:
> > On 5/14/2019 7:07 AM, prakhar srivastava wrote:
> > > On Mon, May 13, 2019 at 6:48 AM Roberto Sassu <roberto.sassu@xxxxxxxxxx> wrote:
> > > > On 5/11/2019 12:37 AM, Prakhar Srivastava wrote:
> > > > > From: Prakhar Srivastava <prsriva02@xxxxxxxxx>
> > > > >
> > > > > The buffer(cmdline args) added to the ima log cannot be attested
> > > > > without having the actual buffer. Thus to make the measured buffer
> > > > > available to store/read a new ima template (buf) is added.
> > > >
> > > > Hi Prakhar
> > > >
> > > > please fix the typos. More comments below.
> > > >
> > > >
> > > > > +     buffer_event_data->type = IMA_XATTR_BUFFER;
> > > > > +     buffer_event_data->buf_length = size;
> > > > > +     memcpy(buffer_event_data->buf, buf, size);
> > > > > +
> > > > > +     event_data.xattr_value = (struct evm_ima_xattr_data *)buffer_event_data;
> > > > > +     event_data.xattr_len = alloc_length;
> > > >
> > > > I would prefer that you introduce two new fields in the ima_event_data
> > > > structure. You can initialize them directly with the parameters of
> > > > process_buffer_measurement().
> > > I will make the edits, this will definitely save the kzalloc in this code
> > > path.
> > > > ima_write_template_field_data() will make
> > > > a copy.
> > > Since event_data->type is used to distinguish what the template field
> > >    should contain.
> > > Removing the type and subsequent check in the template_init,
> > >    buf template fmt will result in the whole event_Data structure
> > > being added to the log, which is not the expected output.
> > > For buffer entries, the buf template fmt will contains the buffer itself.
>
> > The purpose of ima_event_data is to pass data to the init method of
> > template fields. Each method takes the data it needs.
> >
> > If you pass event_data->buf and event_data->buf_len to
> > ima_write_template_field_data() this should be fine.
>
> Hi Roberto,
> I did some testing after making the needed code changes,
> the output is as expected the buf template field only contains
> the buf when the ima_event_data.buf is set.
>
> However i just want to double check if adding two new fields to
> the struct ima_event_data is approach you want me to take?
> Mimi any concerns?

I think it should not be a problem. ima_event_data was introduced to
pass more information to a function for a new template field, without
changing the definition of existing functions.


> what all tests do i need to run to confirm i am not
> in-inadvertently breaking some thing else?

ima_event_data is not used for marshaling/unmarshaling. Adding two new
members to the structure won't change the behavior of existing code.

Roberto


> Thanks,
> Prakhar Srivastava
> > Roberto
> >
> >
> > > > > +      .field_show = ima_show_template_buf},
> > > >
> > > > Please update Documentation/security/IMA-templates.rst
> > > Will update the documentation.
> > >
> > > Thanks,
> > > Prakhar Srivastava
> > > > Thanks
> > > >
> > > > Roberto
> >
> > --
> > HUAWEI TECHNOLOGIES Duesseldorf GmbH, HRB 56063
> > Managing Director: Bo PENG, Jian LI, Yanli SHI

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Managing Director: Bo PENG, Jian LI, Yanli SHI