HID: hid-cypress: validate length of report

BugLink: http://bugs.launchpad.net/bugs/1656876

commit 1ebb7114 upstream.

Make sure we have enough of a report structure to validate before
looking at it.
Reported-by: Benoit Camredon <benoit.camredon@airbus.com>
Tested-by: Benoit Camredon <benoit.camredon@airbus.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

drivers/hid/hid-cypress.c

@@ -39,6 +39,9 @@ static __u8 *cp_report_fixup(struct hid_device *hdev, __u8 *rdesc,
 	if (!(quirks & CP_RDESC_SWAPPED_MIN_MAX))
 		return rdesc;
 
+	if (*rsize < 4)
+		return rdesc;
+
 	for (i = 0; i < *rsize - 4; i++)
 		if (rdesc[i] == 0x29 && rdesc[i + 2] == 0x19) {
 			rdesc[i] = 0x19;