USB: core: prevent malicious bNumInterfaces overflow

USB: core: prevent malicious bNumInterfaces overflow

commit 48a4ff1c7bb5a32d2e396b03132d20d552c0eca7 upstream.

A malicious USB device with crafted descriptors can cause the kernel
to access unallocated memory by setting the bNumInterfaces value too
high in a configuration descriptor.  Although the value is adjusted
during parsing, this adjustment is skipped in one of the error return
paths.

This patch prevents the problem by setting bNumInterfaces to 0
initially.  The existing code already sets it to the proper value
after parsing is complete.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Reported-by: Andrey Konovalov <andreyknvl@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>