linux-kernel - Re: [PATCH RFC 0/4] Add firmware signature file check

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Message-ID: <s5h4nl3i3u6.wl%tiwai@suse.de>
Date:	Tue, 06 Nov 2012 08:32:33 +0100
From:	Takashi Iwai <tiwai@...e.de>
To:	Ming Lei <tom.leiming@...il.com>
Cc:	Matthew Garrett <mjg59@...f.ucam.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>, joeyli <jlee@...e.com>,
	Jiri Kosina <jkosina@...e.cz>,
	David Howells <dhowells@...hat.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org, linux-efi@...r.kernel.org
Subject: Re: [PATCH RFC 0/4] Add firmware signature file check

At Tue, 6 Nov 2012 15:16:43 +0800,
Ming Lei wrote:
> 
> On Tue, Nov 6, 2012 at 3:03 PM, Takashi Iwai <tiwai@...e.de> wrote:
> >
> > Yeah, it's just uncovered in the patch.  As a easy solution, apply the
> > patch like below to disallow the udev fw loading when signature check
> > is enforced.
> >
> >
> > thanks,
> >
> > Takashi
> >
> > ---
> > diff --git a/drivers/base/firmware_class.c b/drivers/base/firmware_class.c
> > index 575bc4c..93121c3 100644
> > --- a/drivers/base/firmware_class.c
> > +++ b/drivers/base/firmware_class.c
> > @@ -912,6 +912,13 @@ static int _request_firmware_load(struct firmware_priv *fw_priv, bool uevent,
> >                 goto handle_fw;
> >         }
> >
> > +       /* signature check isn't handled via udev fw loading */
> > +       if (sig_enforce) {
> > +               fw_load_abort(fw_priv);
> > +               direct_load = 1;
> > +               goto handle_fw;
> > +       }
> > +
> 
> The above might be wrong if the firmware file doesn't exist in default
> search paths.

Heh, I didn't call it's a perfect patch.  It's just an easy solution,
as mentioned.

> You should skip loading from user space only if
> verify_signature() returns false. And the udev loading should be
> resorted to if there is no such firmware file in default search paths.

... and the kernel should ask udev again for the corresponding
signature.  I'm too lazy to implement that just for unknown corner
cases, so put the patch like above.

Honestly speaking, I have a feeling that we should rather go for
getting rid of udev fw loading.  The fw loader code is overly complex
just for udev handshaking. 

Do you know how many firmwares still rely on udev...?


thanks,

Takashi
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