[4.2.y-ckt stable] Patch "USB: usbip: fix potential out-of-bounds write" has been added to the 4.2.y-ckt tree

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    USB: usbip: fix potential out-of-bounds write

to the linux-4.2.y-queue branch of the 4.2.y-ckt extended stable tree 
which can be found at:

    https://git.launchpad.net/~canonical-kernel/linux/+git/linux-stable-ckt/log/?h=linux-4.2.y-queue

This patch is scheduled to be released in version 4.2.8-ckt10.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 4.2.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

---8<------------------------------------------------------------

>From 7679a59d1f2269fb08f5cadd6e9e20ff63e29eb7 Mon Sep 17 00:00:00 2001
From: Ignat Korchagin <ignat.korchagin at gmail.com>
Date: Thu, 17 Mar 2016 18:00:29 +0000
Subject: USB: usbip: fix potential out-of-bounds write

commit b348d7dddb6c4fbfc810b7a0626e8ec9e29f7cbb upstream.

Fix potential out-of-bounds write to urb->transfer_buffer
usbip handles network communication directly in the kernel. When receiving a
packet from its peer, usbip code parses headers according to protocol. As
part of this parsing urb->actual_length is filled. Since the input for
urb->actual_length comes from the network, it should be treated as untrusted.
Any entity controlling the network may put any value in the input and the
preallocated urb->transfer_buffer may not be large enough to hold the data.
Thus, the malicious entity is able to write arbitrary data to kernel memory.

Signed-off-by: Ignat Korchagin <ignat.korchagin at gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
Reference: CVE-2016-3955
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 drivers/usb/usbip/usbip_common.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/drivers/usb/usbip/usbip_common.c b/drivers/usb/usbip/usbip_common.c
index facaaf0..e40da77 100644
--- a/drivers/usb/usbip/usbip_common.c
+++ b/drivers/usb/usbip/usbip_common.c
@@ -741,6 +741,17 @@ int usbip_recv_xbuff(struct usbip_device *ud, struct urb *urb)
 	if (!(size > 0))
 		return 0;

+	if (size > urb->transfer_buffer_length) {
+		/* should not happen, probably malicious packet */
+		if (ud->side == USBIP_STUB) {
+			usbip_event_add(ud, SDEV_EVENT_ERROR_TCP);
+			return 0;
+		} else {
+			usbip_event_add(ud, VDEV_EVENT_ERROR_TCP);
+			return -EPIPE;
+		}
+	}
+
 	ret = usbip_recv(ud->tcp_socket, urb->transfer_buffer, size);
 	if (ret != size) {
 		dev_err(&urb->dev->dev, "recv xbuf, %d\n", ret);
--
2.7.4