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

[Guenter Roeck]

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@xxxxxxxxxx>
Cc: Jani Nikula <jani.nikula@xxxxxxxxx>
Cc: Thomas Zimmermann <tzimmermann@xxxxxxx>
Cc: Danilo Krummrich <dakr@xxxxxxxxxx>
Cc: Maxime Ripard <mripard@xxxxxxxxxx>
Signed-off-by: Guenter Roeck <linux@xxxxxxxxxxxx>
---
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)))
 			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))) {
 			nvif_object_dtor(object);
 			return -ENOMEM;
 		}
-- 
2.39.2