linux-kernel - Re: [PATCH] drm/nouveau/nvif: Avoid build error due to potential integer overflows

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Message-ID: <03cc262da2a3db817aa5663fbce6c914708b74f8.camel@perches.com>
Date: Sat, 18 May 2024 18:19:18 -0700
From: Joe Perches <joe@...ches.com>
To: Guenter Roeck <linux@...ck-us.net>, Kees Cook <keescook@...omium.org>, 
	Christophe JAILLET <christophe.jaillet@...adoo.fr>
Cc: airlied@...il.com, dakr@...hat.com, daniel@...ll.ch, 
 dri-devel@...ts.freedesktop.org, jani.nikula@...el.com, javierm@...hat.com,
  kherbst@...hat.com, linux-kernel@...r.kernel.org, lyude@...hat.com, 
 mripard@...nel.org, nouveau@...ts.freedesktop.org, tzimmermann@...e.de, 
 linux-hardening@...r.kernel.org
Subject: Re: [PATCH] drm/nouveau/nvif: Avoid build error due to potential
 integer overflows

On Sat, 2024-05-18 at 11:23 -0700, Guenter Roeck wrote:
> On 5/18/24 10:32, Kees Cook wrote:
> 
[]
> > I think the INT_MAX test is actually better in this case because
> > nvif_object_ioctl()'s size argument is u32:
> > 
> > ret = nvif_object_ioctl(object, args, sizeof(*args) + size, NULL);
> >                                        ^^^^^^^^^^^^^^^^^^^^
> > 
> > So that could wrap around, even though the allocation may not.
> > 
> > Better yet, since "sizeof(*args) + size" is repeated 3 times in the
> > function, I'd recommend:
> > 
> > 	...
> > 	u32 args_size;
> > 
> > 	if (check_add_overflow(sizeof(*args), size, &args_size))
> > 		return -ENOMEM;
> > 	if (args_size > sizeof(stack)) {
> > 		if (!(args = kmalloc(args_size, GFP_KERNEL)))

trivia:

More typical kernel style would use separate alloc and test

		args = kmalloc(args_size, GFP_KERNEL);
		if (!args)

> > 			return -ENOMEM;
> >          } else {
> >                  args = (void *)stack;
> >          }
> > 	...
> >          ret = nvif_object_ioctl(object, args, args_size, NULL);
> > 
> > This will catch the u32 overflow to nvif_object_ioctl(), catch an
> > allocation underflow on 32-bits systems, and make the code more
> > readable. :)
> > 
> 
> Makes sense. I'll change that and send v2.
> 
> Thanks,
> Guenter
> 
>