Re: [PATCH 2/3] drm/nouveau: Fix NULL pointer dereference in GET_ZCULL_INFO ioctl

[lyude]

Reviewed-by: Lyude Paul <lyude@xxxxxxxxxx>

Will push to drm-misc-fixes in just a moment

On Fri, 2026-10-02 at 12:09 -0600, Jim Cromie via B4 Relay wrote:
> From: Jim Cromie <jim.cromie@xxxxxxxxx>
> 
> When graphics engine firmware fails to load or initialization aborts
> early, nvxx_gr(drm) returns NULL. Calling
> DRM_IOCTL_NOUVEAU_GET_ZCULL_INFO
> causes nouveau_abi16_ioctl_get_zcull_info() to dereference gr at
> offset
> 0xf0 without checking for NULL, triggering a kernel page fault.
> 
> Validate that gr is non-NULL before inspecting gr->has_zcull_info.
> 
> Signed-off-by: Jim Cromie <jim.cromie@xxxxxxxxx>
> ---
> Aug 14 09:21:52 frodo kernel: BUG: kernel NULL pointer dereference,
> address: 00000000000000f0
> Aug 14 09:21:52 frodo kernel: #PF: error_code(0x0000) - not-present
> page
> Aug 14 09:21:52 frodo kernel: Oops: Oops: 0000 [#1] SMP NOPTI
> Aug 14 09:21:52 frodo kernel: RIP:
> 0010:nouveau_abi16_ioctl_get_zcull_info+0x17/0xa0 [nouveau]
> Aug 14 09:21:52 frodo kernel: Code: 00 00 00 90 90 90 90 90 90 90 90
> 90 90 90 90 90 90 90 90 f3 0f 1e fa 0f 1f 44 00 00 48 8b 47 40 48 8b
> 00 48 8b 80 70 02 00 00 <80> b8 f0 00 00 00 00 74 72 8b 90 c0 00 00
> 00 89 16 8b 90 c4 00 00
> Aug 14 09:21:52 frodo kernel: Call Trace:
> Aug 14 09:21:52 frodo kernel:  <TASK>
> Aug 14 09:21:52 frodo kernel:  drm_ioctl_kernel+0xae/0x100
> Aug 14 09:21:52 frodo kernel:  drm_ioctl+0x2e0/0x560
> Aug 14 09:21:52 frodo kernel:  ?
> __pfx_nouveau_abi16_ioctl_get_zcull_info+0x10/0x10 [nouveau]
> Aug 14 09:21:52 frodo kernel:  nouveau_drm_ioctl+0x58/0xc0 [nouveau]
> Aug 14 09:21:52 frodo kernel:  __x64_sys_ioctl+0xb9/0x100
> Aug 14 09:21:52 frodo kernel:  do_syscall_64+0xe2/0x560
> Aug 14 09:21:52 frodo kernel: 
> entry_SYSCALL_64_after_hwframe+0x76/0x7e
> Aug 14 09:21:52 frodo kernel:  </TASK>
> ---
>  drivers/gpu/drm/nouveau/nouveau_abi16.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/nouveau/nouveau_abi16.c
> b/drivers/gpu/drm/nouveau/nouveau_abi16.c
> index cb1810dee8e5..0871ac025ace 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_abi16.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_abi16.c
> @@ -357,7 +357,7 @@
> nouveau_abi16_ioctl_get_zcull_info(ABI16_IOCTL_ARGS)
>  	struct nvkm_gr *gr = nvxx_gr(drm);
>  	struct drm_nouveau_get_zcull_info *out = data;
>  
> -	if (gr->has_zcull_info) {
> +	if (gr && gr->has_zcull_info) {
>  		const struct nvkm_gr_zcull_info *i = &gr-
> >zcull_info;
>  
>  		out->width_align_pixels = i->width_align_pixels;