[sane-devel] Problem with libusb and 64 bits 2.6.25 kernel

[Dennis Lou]

FYI, I managed to scrape together a spare machine for testing and the patch works fine here.

-Dennis

----- Original Message ----
From: Sam Varshavchik <mrsam at courier-mta.com>
To: Dennis Lou <dlou99 at yahoo.com>
Cc: Nicolas <nicolas.martin at freesurf.fr>; mrsam-guest <mrsam-guest at alioth.debian.org>; sane-devel <sane-devel at lists.alioth.debian.org>
Sent: Wednesday, June 25, 2008 3:20:22 PM
Subject: Re: [sane-devel] Problem with libusb and 64 bits 2.6.25 kernel

Dennis Lou writes:

> The way I see it, Sam's buffer overflow concern is predicated on a
> misbehaving device.  I haven't witnessed it but it is possible given that
> we're reverse engineering things rather than working from a formal spec. 
> Nicolas' buffer overflow concern is predicated on a misbehaving usb stack.
>  It's also possible, but probably less likely than Sam's concern.  Which
> to implement depends on how paranoid you are about the behavior of the
> device and libusb.

Clarification: my patch is needed to fix the following bug, referenced 
earlier in the thread:

>>> Hi Dennis, 
>>> 
>>> A bug was opened a while back by Sam Varshavchik, concerning the pixma
>>> backend for Canon ImageClass MF-4270, when compiled and used on a 64
>>> bits platform (no issue so far on 32 bits), details are given here:
>>> 
>>> https://alioth.debian.org/tracker/?group_id=30186&atid=410366&func=detail&aid=310861

The original code issues a read request to libusb for more bytes than 
actually expected, and, apparently, on some hardware that causes a USB 
timeout, with Various Bad Things™, as I described in the bug. Besides a 
single scan now taking ~30 minutes, the resulting pnm is corrupted.

By changing the code not to ask to read more than what's expected, that 
fixes both the original bug, and the overflow problem.