Nouveau - May 2024 - [PATCH] drm/nouveau/nvif: Avoid build error due to potential integer overflows

(adding linux-hardening at vger.kernel.org)


Le 18/05/2024 ? 16:37, Guenter Roeck a ?crit?:
> Trying to build parisc:allmodconfig with gcc 12.x or later results
> in the following build error.
> 
> drivers/gpu/drm/nouveau/nvif/object.c: In function
'nvif_object_mthd':
> drivers/gpu/drm/nouveau/nvif/object.c:161:9: error:
> 	'memcpy' accessing 4294967264 or more bytes at offsets 0 and 32
overlaps 6442450881 bytes at offset -2147483617 [-Werror=restrict]
>    161 |         memcpy(data, args->mthd.data, size);
>        |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> drivers/gpu/drm/nouveau/nvif/object.c: In function
'nvif_object_ctor':
> drivers/gpu/drm/nouveau/nvif/object.c:298:17: error:
> 	'memcpy' accessing 4294967240 or more bytes at offsets 0 and 56
overlaps 6442450833 bytes at offset -2147483593 [-Werror=restrict]
>    298 |                 memcpy(data, args->new.data, size);
> 
> gcc assumes that 'sizeof(*args) + size' can overflow, which would
result
> in the problem.
> 
> The problem is not new, only it is now no longer a warning but an error
since W=1
> has been enabled for the drm subsystem and since Werror is enabled for test
builds.
> 
> Rearrange arithmetic and add extra size checks to avoid the overflow.
> 
> Fixes: a61ddb4393ad ("drm: enable (most) W=1 warnings by default
across the subsystem")
> Cc: Javier Martinez Canillas <javierm-H+wXaHxf7aLQT0dZR+AlfA at
public.gmane.org>
> Cc: Jani Nikula <jani.nikula-ral2JQCrhuEAvxtiuMwx3w at
public.gmane.org>
> Cc: Thomas Zimmermann <tzimmermann-l3A5Bk7waGM at public.gmane.org>
> Cc: Danilo Krummrich <dakr-H+wXaHxf7aLQT0dZR+AlfA at
public.gmane.org>
> Cc: Maxime Ripard <mripard-DgEjT+Ai2ygdnm+yROfE0A at
public.gmane.org>
> Signed-off-by: Guenter Roeck <linux-0h96xk9xTtrk1uMJSBkQmQ at
public.gmane.org>
> ---
> checkpatch complains about the line length in the description and the
(pre-existing)
> assignlemts in if conditions, but I did not want to split lines in the
description
> or rearrange the code further.
> 
> I don't know why I only see the problem with parisc builds (at least so
far).
> 
>   drivers/gpu/drm/nouveau/nvif/object.c | 8 +++++---
>   1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/nouveau/nvif/object.c
b/drivers/gpu/drm/nouveau/nvif/object.c
> index 4d1aaee8fe15..baf623a48874 100644
> --- a/drivers/gpu/drm/nouveau/nvif/object.c
> +++ b/drivers/gpu/drm/nouveau/nvif/object.c
> @@ -145,8 +145,9 @@ nvif_object_mthd(struct nvif_object *object, u32 mthd,
void *data, u32 size)
>   	u8 stack[128];
>   	int ret;
>   
> -	if (sizeof(*args) + size > sizeof(stack)) {
> -		if (!(args = kmalloc(sizeof(*args) + size, GFP_KERNEL)))
> +	if (size > sizeof(stack) - sizeof(*args)) {
> +		if (size > INT_MAX ||
> +		    !(args = kmalloc(sizeof(*args) + size, GFP_KERNEL)))
Hi,

Would it be cleaner or better to use size_add(sizeof(*args), size)?
>   			return -ENOMEM;
>   	} else {
>   		args = (void *)stack;
> @@ -276,7 +277,8 @@ nvif_object_ctor(struct nvif_object *parent, const char
*name, u32 handle,
>   	object->map.size = 0;
>   
>   	if (parent) {
> -		if (!(args = kmalloc(sizeof(*args) + size, GFP_KERNEL))) {
> +		if (size > INT_MAX ||
> +		    !(args = kmalloc(sizeof(*args) + size, GFP_KERNEL))) {
Same.

CJ
>   			nvif_object_dtor(object);
>   			return -ENOMEM;
>   		}

On Sat, May 18, 2024 at 06:54:36PM +0200, Christophe JAILLET
wrote:
> (adding linux-hardening at vger.kernel.org)
> 
> 
> Le 18/05/2024 ? 16:37, Guenter Roeck a ?crit?:
> > Trying to build parisc:allmodconfig with gcc 12.x or later results
> > in the following build error.
> > 
> > drivers/gpu/drm/nouveau/nvif/object.c: In function
'nvif_object_mthd':
> > drivers/gpu/drm/nouveau/nvif/object.c:161:9: error:
> > 	'memcpy' accessing 4294967264 or more bytes at offsets 0 and
32 overlaps 6442450881 bytes at offset -2147483617 [-Werror=restrict]
> >    161 |         memcpy(data, args->mthd.data, size);
> >        |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > drivers/gpu/drm/nouveau/nvif/object.c: In function
'nvif_object_ctor':
> > drivers/gpu/drm/nouveau/nvif/object.c:298:17: error:
> > 	'memcpy' accessing 4294967240 or more bytes at offsets 0 and
56 overlaps 6442450833 bytes at offset -2147483593 [-Werror=restrict]
> >    298 |                 memcpy(data, args->new.data, size);
> > 
> > gcc assumes that 'sizeof(*args) + size' can overflow, which
would result
> > in the problem.
> > 
> > The problem is not new, only it is now no longer a warning but an
error since W=1
> > has been enabled for the drm subsystem and since Werror is enabled for
test builds.
> > 
> > Rearrange arithmetic and add extra size checks to avoid the overflow.
> > 
> > Fixes: a61ddb4393ad ("drm: enable (most) W=1 warnings by default
across the subsystem")
> > Cc: Javier Martinez Canillas <javierm-H+wXaHxf7aLQT0dZR+AlfA at
public.gmane.org>
> > Cc: Jani Nikula <jani.nikula-ral2JQCrhuEAvxtiuMwx3w at
public.gmane.org>
> > Cc: Thomas Zimmermann <tzimmermann-l3A5Bk7waGM at
public.gmane.org>
> > Cc: Danilo Krummrich <dakr-H+wXaHxf7aLQT0dZR+AlfA at
public.gmane.org>
> > Cc: Maxime Ripard <mripard-DgEjT+Ai2ygdnm+yROfE0A at
public.gmane.org>
> > Signed-off-by: Guenter Roeck <linux-0h96xk9xTtrk1uMJSBkQmQ at
public.gmane.org>
> > ---
> > checkpatch complains about the line length in the description and the
(pre-existing)
> > assignlemts in if conditions, but I did not want to split lines in the
description
> > or rearrange the code further.
> > 
> > I don't know why I only see the problem with parisc builds (at
least so far).
> > 
> >   drivers/gpu/drm/nouveau/nvif/object.c | 8 +++++---
> >   1 file changed, 5 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/nouveau/nvif/object.c
b/drivers/gpu/drm/nouveau/nvif/object.c
> > index 4d1aaee8fe15..baf623a48874 100644
> > --- a/drivers/gpu/drm/nouveau/nvif/object.c
> > +++ b/drivers/gpu/drm/nouveau/nvif/object.c
> > @@ -145,8 +145,9 @@ nvif_object_mthd(struct nvif_object *object, u32
mthd, void *data, u32 size)
> >   	u8 stack[128];
> >   	int ret;
> > -	if (sizeof(*args) + size > sizeof(stack)) {
> > -		if (!(args = kmalloc(sizeof(*args) + size, GFP_KERNEL)))
> > +	if (size > sizeof(stack) - sizeof(*args)) {
> > +		if (size > INT_MAX ||
> > +		    !(args = kmalloc(sizeof(*args) + size, GFP_KERNEL)))
> 
> Hi,
> 
> Would it be cleaner or better to use size_add(sizeof(*args), size)?
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)))
			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. :)

-Kees

-- 
Kees Cook