[PATCH 4.4 27/47] USB: core: harden cdc_parse_cdc_header

[Greg Kroah-Hartman]

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Greg Kroah-Hartman <gre...@linuxfoundation.org>

commit 2e1c42391ff2556387b3cb6308b24f6f65619feb upstream.

Andrey Konovalov reported a possible out-of-bounds problem for the
cdc_parse_cdc_header function.  He writes:
        It looks like cdc_parse_cdc_header() doesn't validate buflen
        before accessing buffer[1], buffer[2] and so on. The only check
        present is while (buflen > 0).

So fix this issue up by properly validating the buffer length matches
what the descriptor says it is.

Reported-by: Andrey Konovalov <andreyk...@google.com>
Tested-by: Andrey Konovalov <andreyk...@google.com>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

---
 drivers/net/usb/usbnet.c |    4 ++++
 1 file changed, 4 insertions(+)

--- a/drivers/net/usb/usbnet.c
+++ b/drivers/net/usb/usbnet.c
@@ -1990,6 +1990,10 @@ int cdc_parse_cdc_header(struct usb_cdc_
                        elength = 1;
                        goto next_desc;
                }
+               if ((buflen < elength) || (elength < 3)) {
+                       dev_err(&intf->dev, "invalid descriptor buffer 
length\n");
+                       break;
+               }
                if (buffer[1] != USB_DT_CS_INTERFACE) {
                        dev_err(&intf->dev, "skipping garbage\n");
                        goto next_desc;