linux-kernel - Re: /drivers/char/Kconfig Bug Kernel Patch

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Date:   Tue, 13 Dec 2016 14:42:18 -0800
From:   Max Bires <jbires@...gle.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     gregkh@...uxfoundation.org, josh@...htriplett.org,
        linux-kernel@...r.kernel.org
Subject: Re: /drivers/char/Kconfig Bug Kernel Patch

On Tue, Dec 13, 2016 at 1:37 PM, Arnd Bergmann <arnd@...db.de> wrote:
>
> On Tuesday, December 13, 2016 1:30:39 PM CET Max Bires wrote:
> > While trying to turn off the port device in defconfig, I ran into a bug
> > caused by the fact that the Kconfig for port didn't have a string after the
> > bool declaration. I fixed this in the attached patch (though I figure the
> > description might need tuning up). Let me know if there's anything else I
> > need to do.
>
> The change looks reasonable, however there are a few things to improve
> to get the patch applied:
>
> - clarify that the current behavior is not a bug, but was done intentionally.
>   Making the option user-visible would help avoid a potential attack vector
>   and make the kernel smaller, both of which are useful.
>
> - remove the "Change-id" line from the submission, it has no meaning in
>   an upstream kernel
>
> - send the patch inline rather than as an attachment, this is usually done
>   with git-send-email.
>
>         Arnd
-First and second points have been addressed; I had some trouble with
send-email, so let me know if the following isn't acceptable inlining.

>From c4a21c2ac0c587094000a3daeb13eec6056dc63f Mon Sep 17 00:00:00 2001
From: Max <jbires@...gle.com>
Date: Fri, 9 Dec 2016 15:16:47 -0800
Subject: [PATCH] char: lack of bool string made CONFIG_DEVPORT always on

Without a bool string present, using "# CONFIG_DEVPORT is not set" in
defconfig files would not actually unset devport. This ensured that
/dev/port was always on, but there are reasons a user may wish to disable
it (smaller kernel, attack surface reduction) if it's not being used. Adding
a message here in order to make this user visible.

Signed-off-by: Max Bires <jbires@...gle.com>
---
 drivers/char/Kconfig | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/char/Kconfig b/drivers/char/Kconfig
index 7ad3127..70e626c 100644
--- a/drivers/char/Kconfig
+++ b/drivers/char/Kconfig
@@ -589,10 +589,13 @@ config TELCLOCK
 	  controlling the behavior of this hardware.

 config DEVPORT
-	bool
+	bool "/dev/port character device"
 	depends on !M68K
 	depends on ISA || PCI
 	default y
+  help
+    Say Y here if you want to support the /dev/port device. The
+	  /dev/port device is similar to /dev/mem, but for I/O ports.

 config DCC_TTY
 	tristate "DCC tty driver"
-- 
2.8.0.rc3.226.g39d4020