[PATCH AUTOSEL 4.9 08/19] cdc_ncm: fix divide-by-zero caused by invalid wMaxPacketSize

[Sasha Levin]

From: BjÃrn Mork <bjorn@xxxxxxx>

[ Upstream commit 3fe4b3351301660653a2bc73f2226da0ebd2b95e ]

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@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: BjÃrn Mork <bjorn@xxxxxxx>
Signed-off-by: Jakub Kicinski <jakub.kicinski@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 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 7b158674ceeda..43e28d2b0de7f 100644
--- a/drivers/net/usb/cdc_ncm.c
+++ b/drivers/net/usb/cdc_ncm.c
@@ -679,8 +679,12 @@ 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