linux-kernel - Re: [PATCH] USB: don't read past config->interface[] if usb_control_msg() fails in usb_reset

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Date:	Tue, 9 Feb 2010 10:12:53 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Roel Kluin <roel.kluin@...il.com>
cc:	Greg Kroah-Hartman <gregkh@...e.de>,
	<sarah.a.sharp@...ux.intel.com>, <linux-usb@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] USB: don't read past config->interface[] if usb_control_msg()
 fails in usb_reset_configuration()

On Tue, 9 Feb 2010, Roel Kluin wrote:

> After the loop `for (i = 0; i < config->desc.bNumInterfaces; i++)' if no
> break occurred, i equals config->desc.bNumInterfaces. so if
> usb_control_msg() failed then after goto reset_old_alts we read from
> config->interface[config->desc.bNumInterfaces].

You correctly identified a problem, but your fix is wrong -- or at 
least, it is much too complicated.  The proper fix goes like this:

 	/* If not, reinstate the old alternate settings */
 	if (retval < 0) {
 reset_old_alts:
-		for (; i >= 0; i--) {
+		for (i--; i >= 0; i--) {
 			struct usb_interface *intf = config->interface[i];
 			struct usb_host_interface *alt;
 

Alan Stern

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