usb/80829: possible panic when loading USB-modules

[Warner Losh]

The following reply was made to PR usb/80829; it has been noted by GNATS.

From: Warner Losh <imp at bsdimp.com>
To: hselasky at c2i.net
Cc: FreeBSD-gnats-submit at FreeBSD.ORG
Subject: Re: usb/80829: possible panic when loading USB-modules
Date: Mon, 09 May 2005 11:01:53 -0600 (MDT)

 > There is a special mechanism where probe/attach can clear an entry in the 
 > array pointed to by "uaa->ifaces". The existing USB-driver allocates the 
 > "uaa" in memory, but the "uaa->ifaces" is still on the stack ! This is going 
 > to cause a panic for some devices when loaded as a module.
 > 
 > usbd_status
 > usbd_probe_and_attach(device_ptr_t parent, usbd_device_handle dev,
 >                       int port, int addr)
 > 
 > ...
 >         usbd_interface_handle ifaces[256]; /* 256 is the absolute max */
 > 
 > ...
 >   uaa.ifaces = ifaces;
 
 Good catch!
 
 > Allocate "ifaces" structure in memory, and make sure it gets freed, or revert 
 > everything back to stack, which is way simpler!
 
 Can't go back to the stack method.  It doesn't work.  Since we can
 retain devices past the function call to usbd_probe_and_attach, we
 can't rely on anything on the stack.  The problem here I believe is an
 oversight on my part when I did that code.
 
 Warner