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");