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

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Message-ID: <ec8ee6f7-3a1d-6498-e009-f85e677b448a@huawei.com>
Date:   Tue, 14 May 2019 15:22:46 +0200
From:   Roberto Sassu <roberto.sassu@...wei.com>
To:     prakhar srivastava <prsriva02@...il.com>
CC:     <linux-integrity@...r.kernel.org>,
        <inux-security-module@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, Mimi Zohar <zohar@...ux.ibm.com>,
        <ebiederm@...ssion.com>, <vgoyal@...hat.com>,
        Prakhar Srivastava <prsriva@...rosoft.com>
Subject: Re: [PATCH 2/3 v5] add a new template field buf to contain the buffer

On 5/14/2019 7:07 AM, prakhar srivastava wrote:
> On Mon, May 13, 2019 at 6:48 AM Roberto Sassu <roberto.sassu@...wei.com> wrote:
>>
>> On 5/11/2019 12:37 AM, Prakhar Srivastava wrote:
>>> From: Prakhar Srivastava <prsriva02@...il.com>
>>>
>>> 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 templet 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.

Roberto


>>> +      .field_show = ima_show_template_buf},
>>
>> Please update Documentation/security/IMA-templates.rst
> Will update the documentation.
> 
> Thanks,
> Prakhar Srivastava
>>
>> Thanks
>>
>> Roberto

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