From: Oliver Neukum <oneukum@suse.com>
Date: Thu, 7 Nov 2019 09:48:01 +0100
Subject: CDC-NCM: handle incomplete transfer of MTU
Git-commit: 332f989a3b0041b810836c5c3747e59aad7e9d0b
Patch-mainline: 5.4-rc7
References: networking-stable-19_11_10

A malicious device may give half an answer when asked
for its MTU. The driver will proceed after this with
a garbage MTU. Anything but a complete answer must be treated
as an error.

V2: used sizeof as request by Alexander

Reported-and-tested-by: syzbot+0631d878823ce2411636@syzkaller.appspotmail.com
Signed-off-by: Oliver Neukum <oneukum@suse.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
 drivers/net/usb/cdc_ncm.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

--- a/drivers/net/usb/cdc_ncm.c
+++ b/drivers/net/usb/cdc_ncm.c
@@ -576,8 +576,8 @@ static void cdc_ncm_set_dgram_size(struc
 	/* read current mtu value from device */
 	err = usbnet_read_cmd(dev, USB_CDC_GET_MAX_DATAGRAM_SIZE,
 			      USB_TYPE_CLASS | USB_DIR_IN | USB_RECIP_INTERFACE,
-			      0, iface_no, &max_datagram_size, 2);
-	if (err < 0) {
+			      0, iface_no, &max_datagram_size, sizeof(max_datagram_size));
+	if (err < sizeof(max_datagram_size)) {
 		dev_dbg(&dev->intf->dev, "GET_MAX_DATAGRAM_SIZE failed\n");
 		goto out;
 	}
@@ -588,7 +588,7 @@ static void cdc_ncm_set_dgram_size(struc
 	max_datagram_size = cpu_to_le16(ctx->max_datagram_size);
 	err = usbnet_write_cmd(dev, USB_CDC_SET_MAX_DATAGRAM_SIZE,
 			       USB_TYPE_CLASS | USB_DIR_OUT | USB_RECIP_INTERFACE,
-			       0, iface_no, &max_datagram_size, 2);
+			       0, iface_no, &max_datagram_size, sizeof(max_datagram_size));
 	if (err < 0)
 		dev_dbg(&dev->intf->dev, "SET_MAX_DATAGRAM_SIZE failed\n");