linux-kernel - [ 017/153] staging: comedi: disallow COMEDI

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Message-Id: <20130304033709.244001909@decadent.org.uk>
Date:	Mon, 04 Mar 2013 03:37:24 +0000
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	akpm@...ux-foundation.org, Ian Abbott <abbotti@....co.uk>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: [ 017/153] staging: comedi: disallow COMEDI_DEVCONFIG on non-board minors

3.2-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Ian Abbott <abbotti@....co.uk>

commit 754ab5c0e55dd118273ca2c217c4d95e9fbc8259 upstream.

Comedi has two sorts of minor devices:
(a) normal board minor devices in the range 0 to
COMEDI_NUM_BOARD_MINORS-1 inclusive; and
(b) special subdevice minor devices in the range COMEDI_NUM_BOARD_MINORS
upwards that are used to open the same underlying comedi device as the
normal board minor devices, but with non-default read and write
subdevices for asynchronous commands.

The special subdevice minor devices get created when a board supporting
asynchronous commands is attached to a normal board minor device, and
destroyed when the board is detached from the normal board minor device.
One way to attach or detach a board is by using the COMEDI_DEVCONFIG
ioctl.  This should only be used on normal board minors as the special
subdevice minors are too ephemeral.  In particular, the change
introduced in commit 7d3135af399e92cf4c9bbc5f86b6c140aab3b88c ("staging:
comedi: prevent auto-unconfig of manually configured devices") breaks
horribly for special subdevice minor devices.

Since there's no legitimate use for the COMEDI_DEVCONFIG ioctl on a
special subdevice minor device node, disallow it and return -ENOTTY.

Signed-off-by: Ian Abbott <abbotti@....co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/staging/comedi/comedi_fops.c |    5 +++++
 1 file changed, 5 insertions(+)

--- a/drivers/staging/comedi/comedi_fops.c
+++ b/drivers/staging/comedi/comedi_fops.c
@@ -136,6 +136,11 @@ static long comedi_unlocked_ioctl(struct
 	/* Device config is special, because it must work on
 	 * an unconfigured device. */
 	if (cmd == COMEDI_DEVCONFIG) {
+		if (minor >= COMEDI_NUM_BOARD_MINORS) {
+			/* Device config not appropriate on non-board minors. */
+			rc = -ENOTTY;
+			goto done;
+		}
 		rc = do_devconfig_ioctl(dev,
 					(struct comedi_devconfig __user *)arg);
 		goto done;

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