Subject: Re: KMSAN: uninit-value in cdc_ncm_set_dgram_size

From: Oliver Neukum <[email-masked]>
Date: Tue, 05 Nov 2019 12:11:56 +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..
> git tree:       https://github.com/google/kmsan.git master
> console output: https://syzkaller.appspot.com/x/log.txt?x=11f103bce00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=9e324dfe9c7b0360
> dashboard link: https://syzkaller.appspot.com/bug?extid=0631d878823ce2411636
> compiler:       clang version 9.0.0 (/home/glider/llvm/clang  
> 80fee25776c2fb61e74c1ecb1a523375c2500b69)
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=10dd9774e00000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=13651a24e00000
> 
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: [email-masked]
#syz test: https://github.com/google/kmsan.git 96c6c319
From 090ac0305bb47da9336c0188e0e59e50ff2243c3 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.

Reported-by: [email-masked]
Signed-off-by: Oliver Neukum <[email-masked]>
---
 drivers/net/usb/cdc_ncm.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/usb/cdc_ncm.c b/drivers/net/usb/cdc_ncm.c
index 00cab3f43a4c..939487a5f4bc 100644
--- a/drivers/net/usb/cdc_ncm.c
+++ b/drivers/net/usb/cdc_ncm.c
@@ -579,7 +579,7 @@ static void cdc_ncm_set_dgram_size(struct usbnet *dev, int new_size)
 	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) {
+	if (err < 2) {
 		dev_dbg(&dev->intf->dev, "GET_MAX_DATAGRAM_SIZE failed\n");
 		goto out;
 	}
-- 
2.16.4