linux-kernel - Re: [PATCH 4/7] firmware_class: perform new LSM checks

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Message-ID: <CAGXu5jK5np62pR4f7_qa_LU97hBN8e1hu998=C4ah+Xyv3eYtg@mail.gmail.com>
Date:	Fri, 18 Jul 2014 10:05:14 -0700
From:	Kees Cook <keescook@...omium.org>
To:	James Morris <jmorris@...ei.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Ming Lei <ming.lei@...onical.com>,
	"Luis R. Rodriguez" <mcgrof@...e.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	James Morris <james.l.morris@...cle.com>,
	David Howells <dhowells@...hat.com>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	linux-security-module <linux-security-module@...r.kernel.org>,
	linux-firmware@...nel.org,
	linux-wireless <linux-wireless@...r.kernel.org>
Subject: Re: [PATCH 4/7] firmware_class: perform new LSM checks

On Thu, Jul 17, 2014 at 8:41 PM, James Morris <jmorris@...ei.org> wrote:
> On Mon, 14 Jul 2014, Kees Cook wrote:
>
>> This attaches LSM hooks to the existing firmware loading interfaces:
>> filesystem-found firmware and demand-loaded blobs.
>
>>  static int fw_get_filesystem_firmware(struct device *device,
>> @@ -640,6 +646,12 @@ static ssize_t firmware_loading_store(struct device *dev,
>>               break;
>>       case 0:
>>               if (test_bit(FW_STATUS_LOADING, &fw_buf->status)) {
>> +                     if (security_kernel_fw_from_file(NULL, fw_buf->data,
>> +                                                      fw_buf->size)) {
>> +                             fw_load_abort(fw_priv);
>> +                             break;
>> +                     }
>> +
>>                       set_bit(FW_STATUS_DONE, &fw_buf->status);
>>                       clear_bit(FW_STATUS_LOADING, &fw_buf->status);
>>
>>
>
> Can you explain the loading store, and what the semantics are for an LSM
> when a NULL is passed as the file?

I'm not sure what you mean by "loading store"?

When NULL is passed as the file, it means that the firmware was passes
a blob, and there is no file backing it:

+ * @kernel_fw_from_file:
+ *     Load firmware from userspace.
+ *     @file contains the file structure pointing to the file containing
+ *     the firmware to load. If the module is being loaded from a blob,
+ *     this argument will be NULL.
+ *     @buf pointer to buffer containing firmware contents.
+ *     @size length of the firmware contents.
+ *     Return 0 if permission is granted.

An LSM that has a policy to require a file to back the firmware would
reject such loads.

-Kees

-- 
Kees Cook
Chrome OS Security
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