[PATCH 5.9 07/15] staging: comedi: check validity of wMaxPacketSize of usb endpoints found

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

From: Anant Thazhemadam <anant.thazhemadam@gmail.com>

commit e1f13c879a7c21bd207dc6242455e8e3a1e88b40 upstream.

While finding usb endpoints in vmk80xx_find_usb_endpoints(), check if
wMaxPacketSize = 0 for the endpoints found.

Some devices have isochronous endpoints that have wMaxPacketSize = 0
(as required by the USB-2 spec).
However, since this doesn't apply here, wMaxPacketSize = 0 can be
considered to be invalid.

Reported-by: syzbot+009f546aa1370056b1c2@syzkaller.appspotmail.com
Tested-by: syzbot+009f546aa1370056b1c2@syzkaller.appspotmail.com
Signed-off-by: Anant Thazhemadam <anant.thazhemadam@gmail.com>
Cc: stable <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20201010082933.5417-1-anant.thazhemadam@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/staging/comedi/drivers/vmk80xx.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/drivers/staging/comedi/drivers/vmk80xx.c
+++ b/drivers/staging/comedi/drivers/vmk80xx.c
@@ -667,6 +667,9 @@ static int vmk80xx_find_usb_endpoints(st
 	if (!devpriv->ep_rx || !devpriv->ep_tx)
 		return -ENODEV;
 
+	if (!usb_endpoint_maxp(devpriv->ep_rx) || !usb_endpoint_maxp(devpriv->ep_tx))
+		return -EINVAL;
+
 	return 0;
 }