[PATCH 4.13 42/44] Input: ims-psu - check if CDC union descriptor is sane

[Greg Kroah-Hartman]

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

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

From: Dmitry Torokhov <dmitry.torok...@gmail.com>

commit ea04efee7635c9120d015dcdeeeb6988130cb67a upstream.

Before trying to use CDC union descriptor, try to validate whether that it
is sane by checking that intf->altsetting->extra is big enough and that
descriptor bLength is not too big and not too small.

Reported-by: Andrey Konovalov <andreyk...@google.com>
Signed-off-by: Dmitry Torokhov <dmitry.torok...@gmail.com>
Cc: Ben Hutchings <ben.hutchi...@codethink.co.uk>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

---
 drivers/input/misc/ims-pcu.c |   16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

--- a/drivers/input/misc/ims-pcu.c
+++ b/drivers/input/misc/ims-pcu.c
@@ -1635,13 +1635,25 @@ ims_pcu_get_cdc_union_desc(struct usb_in
                return NULL;
        }
 
-       while (buflen > 0) {
+       while (buflen >= sizeof(*union_desc)) {
                union_desc = (struct usb_cdc_union_desc *)buf;
 
+               if (union_desc->bLength > buflen) {
+                       dev_err(&intf->dev, "Too large descriptor\n");
+                       return NULL;
+               }
+
                if (union_desc->bDescriptorType == USB_DT_CS_INTERFACE &&
                    union_desc->bDescriptorSubType == USB_CDC_UNION_TYPE) {
                        dev_dbg(&intf->dev, "Found union header\n");
-                       return union_desc;
+
+                       if (union_desc->bLength >= sizeof(*union_desc))
+                               return union_desc;
+
+                       dev_err(&intf->dev,
+                               "Union descriptor to short (%d vs %zd\n)",
+                               union_desc->bLength, sizeof(*union_desc));
+                       return NULL;
                }
 
                buflen -= union_desc->bLength;