Subject: Re: KMSAN: uninit-value in cdc_ncm_set_dgram_size

From: Oliver Neukum <[email-masked]>
Date: Wed, 06 Nov 2019 13:23:32 +0100

Am Mittwoch, den 30.10.2019, 12:22 -0700 schrieb syzbot:
> Hello,
> 
> syzbot found the following crash on:
> 
> HEAD commit:    96c6c319 net: kasan: kmsan: support CONFIG_GENERIC_CSUM on..
#syz test: https://github.com/google/kmsan.git 96c6c319

>From 23a6624cf7d8e146c35f2eec135d6c22e24f9a2e Mon Sep 17 00:00:00 2001
From: Oliver Neukum <[email-masked]>
Date: Tue, 5 Nov 2019 12:04:44 +0100
Subject: [PATCH] CDC-NCM: handle incomplete transfer of MTU

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-by: [email-masked]
Signed-off-by: Oliver Neukum <[email-masked]>
---
 drivers/net/usb/cdc_ncm.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/net/usb/cdc_ncm.c b/drivers/net/usb/cdc_ncm.c
index 00cab3f43a4c..a245597a3902 100644
--- a/drivers/net/usb/cdc_ncm.c
+++ b/drivers/net/usb/cdc_ncm.c
@@ -578,8 +578,8 @@ static void cdc_ncm_set_dgram_size(struct usbnet *dev, int new_size)
 	/* 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;
 	}
@@ -590,7 +590,7 @@ static void cdc_ncm_set_dgram_size(struct usbnet *dev, int new_size)
 	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");
 
-- 
2.16.4