linux-kernel - Re: [PATCH v2 2/2] firmware_class: perform new LSM checks

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Date:	Wed, 23 Jul 2014 12:11:06 +0200
From:	Takashi Iwai <tiwai@...e.de>
To:	Kees Cook <keescook@...omium.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	James Morris <james.l.morris@...cle.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Ming Lei <ming.lei@...onical.com>,
	linux-security-module <linux-security-module@...r.kernel.org>
Subject: Re: [PATCH v2 2/2] firmware_class: perform new LSM checks

At Tue, 22 Jul 2014 10:39:00 -0700,
Kees Cook wrote:
> 
> On Mon, Jul 21, 2014 at 11:55 PM, Takashi Iwai <tiwai@...e.de> wrote:
> > At Mon, 21 Jul 2014 12:06:41 -0700,
> > Kees Cook wrote:
> >>
> >> This attaches LSM hooks to the existing firmware loading interfaces:
> >> filesystem-found firmware and demand-loaded blobs.
> >>
> >> Signed-off-by: Kees Cook <keescook@...omium.org>
> >> Acked-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> >> ---
> >>  drivers/base/firmware_class.c |   16 ++++++++++++++--
> >>  1 file changed, 14 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/drivers/base/firmware_class.c b/drivers/base/firmware_class.c
> >> index d276e33880be..7399bab71ced 100644
> >> --- a/drivers/base/firmware_class.c
> >> +++ b/drivers/base/firmware_class.c
> >> @@ -28,6 +28,7 @@
> >>  #include <linux/suspend.h>
> >>  #include <linux/syscore_ops.h>
> >>  #include <linux/reboot.h>
> >> +#include <linux/security.h>
> >>
> >>  #include <generated/utsrelease.h>
> >>
> >> @@ -308,12 +309,17 @@ static int fw_read_file_contents(struct file *file, struct firmware_buf *fw_buf)
> >>       if (rc != size) {
> >>               if (rc > 0)
> >>                       rc = -EIO;
> >> -             vfree(buf);
> >> -             return rc;
> >> +             goto fail;
> >>       }
> >> +     rc = security_kernel_fw_from_file(file, buf, size);
> >> +     if (rc)
> >> +             goto fail;
> >>       fw_buf->data = buf;
> >>       fw_buf->size = size;
> >>       return 0;
> >> +fail:
> >> +     vfree(buf);
> >> +     return rc;
> >>  }
> >>
> >>  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);
> >
> > security_kernel_fw_from_file() should be called after
> > fw_map_pages_buf() call (that is found after these lines).
> > Otherwise fw_buf->buf won't contain a valid buffer pointer.
> 
> Ah! Good to know. I guess I was getting lucky in my testing. Is this a
> race condition?

This is the code path where direct f/w loading fails but the
user-space helper feeds the data.  Did you test that scenario?


Takashi
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