netdev - [PATCH net,stable] cdc_ncm: fix divide-by-zero caused by invalid wMaxPacketSize

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Date:   Wed, 18 Sep 2019 14:01:46 +0200
From:   Bjørn Mork <bjorn@...k.no>
To:     netdev@...r.kernel.org
Cc:     linux-usb@...r.kernel.org, Oliver Neukum <oliver@...kum.org>,
        Bjørn Mork <bjorn@...k.no>,
        syzbot+ce366e2b8296e25d84f5@...kaller.appspotmail.com
Subject: [PATCH net,stable] cdc_ncm: fix divide-by-zero caused by invalid wMaxPacketSize

Endpoints with zero wMaxPacketSize are not usable for transferring
data. Ignore such endpoints when looking for valid in, out and
status pipes, to make the driver more robust against invalid and
meaningless descriptors.

The wMaxPacketSize of the out pipe is used as divisor. So this change
fixes a divide-by-zero bug.

Reported-by: syzbot+ce366e2b8296e25d84f5@...kaller.appspotmail.com
Signed-off-by: Bjørn Mork <bjorn@...k.no>
---
#syz test: https://github.com/google/kasan.git f0df5c1b

 drivers/net/usb/cdc_ncm.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/net/usb/cdc_ncm.c b/drivers/net/usb/cdc_ncm.c
index 50c05d0f44cb..00cab3f43a4c 100644
--- a/drivers/net/usb/cdc_ncm.c
+++ b/drivers/net/usb/cdc_ncm.c
@@ -681,8 +681,12 @@ cdc_ncm_find_endpoints(struct usbnet *dev, struct usb_interface *intf)
 	u8 ep;
 
 	for (ep = 0; ep < intf->cur_altsetting->desc.bNumEndpoints; ep++) {
-
 		e = intf->cur_altsetting->endpoint + ep;
+
+		/* ignore endpoints which cannot transfer data */
+		if (!usb_endpoint_maxp(&e->desc))
+			continue;
+
 		switch (e->desc.bmAttributes & USB_ENDPOINT_XFERTYPE_MASK) {
 		case USB_ENDPOINT_XFER_INT:
 			if (usb_endpoint_dir_in(&e->desc)) {
-- 
2.20.1