linux-kernel - [047/127] firewire: cdev: fix information leak

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Date:	Tue, 07 Dec 2010 16:43:53 -0800
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Stefan Richter <stefanr@...6.in-berlin.de>,
	maximilian attems <max@...o.at>
Subject: [047/127] firewire: cdev: fix information leak

2.6.32-stable review patch.  If anyone has any objections, please let us know.

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

From: Stefan Richter <stefanr@...6.in-berlin.de>

commit 9cac00b8f0079d5d3d54ec4dae453d58dec30e7c upstream.

A userspace client got to see uninitialized stack-allocated memory if it
specified an _IOC_READ type of ioctl and an argument size larger than
expected by firewire-core's ioctl handlers (but not larger than the
core's union ioctl_arg).

Fix this by clearing the requested buffer size to zero, but only at _IOR
ioctls.  This way, there is almost no runtime penalty to legitimate
ioctls.  The only legitimate _IOR is FW_CDEV_IOC_GET_CYCLE_TIMER with 12
or 16 bytes to memset.

[Another way to fix this would be strict checking of argument size (and
possibly direction) vs. command number.  However, we then need a lookup
table, and we need to allow for slight size deviations in case of 32bit
userland on 64bit kernel.]

Reported-by: Clemens Ladisch <clemens@...isch.de>
Signed-off-by: Stefan Richter <stefanr@...6.in-berlin.de>
[ Backported to 2.6.32 firewire core -maks ]
Signed-off-by: maximilian attems <max@...o.at>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 drivers/firewire/core-cdev.c |   18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

--- a/drivers/firewire/core-cdev.c
+++ b/drivers/firewire/core-cdev.c
@@ -1299,24 +1299,24 @@ static int dispatch_ioctl(struct client
 	int ret;
 
 	if (_IOC_TYPE(cmd) != '#' ||
-	    _IOC_NR(cmd) >= ARRAY_SIZE(ioctl_handlers))
+	    _IOC_NR(cmd) >= ARRAY_SIZE(ioctl_handlers) ||
+	    _IOC_SIZE(cmd) > sizeof(buffer))
 		return -EINVAL;
 
-	if (_IOC_DIR(cmd) & _IOC_WRITE) {
-		if (_IOC_SIZE(cmd) > sizeof(buffer) ||
-		    copy_from_user(buffer, arg, _IOC_SIZE(cmd)))
+	if (_IOC_DIR(cmd) == _IOC_READ)
+		memset(&buffer, 0, _IOC_SIZE(cmd));
+
+	if (_IOC_DIR(cmd) & _IOC_WRITE)
+		if (copy_from_user(buffer, arg, _IOC_SIZE(cmd)))
 			return -EFAULT;
-	}
 
 	ret = ioctl_handlers[_IOC_NR(cmd)](client, buffer);
 	if (ret < 0)
 		return ret;
 
-	if (_IOC_DIR(cmd) & _IOC_READ) {
-		if (_IOC_SIZE(cmd) > sizeof(buffer) ||
-		    copy_to_user(arg, buffer, _IOC_SIZE(cmd)))
+	if (_IOC_DIR(cmd) & _IOC_READ)
+		if (copy_to_user(arg, buffer, _IOC_SIZE(cmd)))
 			return -EFAULT;
-	}
 
 	return ret;
 }


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