linux-kernel - Re: [PATCH] usb: use memdup

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Date:	Wed, 6 May 2009 11:31:17 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Oliver Neukum <oliver@...kum.org>
Cc:	david-b@...bell.net, lihong.hi@...il.com,
	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] usb: use memdup_user()

On Wed, 6 May 2009 15:34:52 +0200
Oliver Neukum <oliver@...kum.org> wrote:

> Am Dienstag, 5. Mai 2009 19:22:53 schrieb Andrew Morton:
> > On Tue, 5 May 2009 12:44:01 +0200 Oliver Neukum <oliver@...kum.org> wrote:
> 
> > > USB drivers are interface level yet some functions, reset and power
> > > management, are on a device level. As it is unpredictable whether
> > > a driver will share a device with a storage driver, all USB drivers as
> > > far as these functions are concerned must be considered block device
> > > drivers. That's the reason GFP_NOIO is so prevalent in USB.
> >
> > There must be some particular action which flips the thread of control
> > from one state to the other.  eg, taking of a lock.
> 
> Basically assigning an interface to the storage or ub driver.

That's hardly enough information for anyone to understand what you
mean :(

Oh well, doesn't matter.

> > > > I wonder how hard it would be to add runtime debugging checks?  If
> > >
> > > I'd prefer compile time checks. Ideally we'd annotate a function with an
> > > attribute making the compiler barf if copy_to/from_user or an
> > > inappropriate kmalloc is used. It can't be perfect due to function
> > > pointers, but it would be a good start.
> >
> > I don't think that would have enough coverage - bugs in this area tend
> > to come from calling some function which looks innocent, but which
> > calls some function which calls some function which calls some function
> > which uses GFP_KERNEL.
> >
> > And then there's stuff like "usb takes a mutex which is also taken by
> > some other thread which does a GFP_KERNEL allocation while holding that
> > mutex".
> 
> Yes, but to catch that you'd have to teach lockdep about those functions
> whose locks are dangerous to share with respect to memory allocation.
> Is there another way to do that besides labelling dangerous methods?

Adding lockdep annotation to the locks, I guess.  Probably a new kind of
annotation.
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