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

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

[Bjørn Mork]

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@syzkaller.appspotmail.com
Signed-off-by: Bjørn Mork <bjorn@mork.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

Re: divide error in cdc_ncm_update_rxtx_max

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger  
crash:

Reported-and-tested-by:  
syzbot+ce366e2b8296e25d84f5@syzkaller.appspotmail.com

Tested on:

commit:         f0df5c1b usb-fuzzer: main usb gadget fuzzer driver
git tree:       https://github.com/google/kasan.git
kernel config:  https://syzkaller.appspot.com/x/.config?x=5c6633fa4ed00be5
dashboard link: https://syzkaller.appspot.com/bug?extid=ce366e2b8296e25d84f5
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
patch:          https://syzkaller.appspot.com/x/patch.diff?x=114971b5600000

Note: testing is done by a robot and is best-effort only.

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

[Jakub Kicinski]

On Wed, 18 Sep 2019 14:01:46 +0200, Bjørn Mork wrote:
> 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@syzkaller.appspotmail.com
> Signed-off-by: Bjørn Mork <bjorn@mork.no>

Applied, queued, thank you!