Firmware signing -- Re: [PATCH 00/27] security, efi: Add kernel lockdown

[Luis R. Rodriguez]

On Wed, Nov 15, 2017 at 06:49:57AM -0500, Mimi Zohar wrote:
> On Tue, 2017-11-14 at 21:50 +0100, Luis R. Rodriguez wrote:
> 
> > Johannes made cfg80211 recently just use request_firmware() now via commit on
> > linux-next 90a53e4432 ("cfg80211: implement regdb signature checking") [0] as
> > he got tired of waiting firmware signing, but note he implemented a signature
> > checking on its own so he open codes verify_pkcs7_signature() after the
> > request_firmware() call. If we are happy to live with this, then so be it.
> > 
> > [0] https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?id=90a53e4432b12288316efaa5f308adafb8d304b0
> 
> Johannes was tired of waiting?  Commit 5a9196d "ima: add support for
> measuring and appraising firmware" has been in the kernel since linux-
> 3.17.
> 
> The original firmware hook for verifying firmware signatures were
> replaced with the common LSM pre and post kernel_read_file() hooks
> in linux-4.6.y.
> 
> Even if you wanted to support firmware signature verification without
> IMA-appraisal, it should be using the LSM hooks.

request_firmware() uses kernel_read_file_from_path() underneath the hood,
and so its used for both:

	/lib/firmware/regulatory.db
	/lib/firmware/regulatory.db.p7s

The later only if CONFIG_CFG80211_REQUIRE_SIGNED_REGDB, which defaults
to y anyway.

What I meant was that net/wireless/reg.c now open codes firmware signature
validation on its own rather than using a helper. IMA appraisal will still
be used if enabled given kernel_read_file_from_path() is used.

The open coding of the firmware signature check is what I wanted to highlight.

  Luis
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