Re: [PATCH v2 1/3] nouveau: Fix NULL pointer dereferences in GETPARAM ioctl

["Danilo Krummrich" <dakr@kernel.org>]

On Fri Oct 9, 2026 at 7:44 PM CEST, Jim Cromie via B4 Relay wrote:
> From: Jim Cromie <jim.cromie@gmail.com>
>
> When hardware or firmware initialization fails, the graphics engine
> (gr) or device functions may remain NULL. Attempting to access these
> during the GETPARAM ioctl (e.g., NOUVEAU_GETPARAM_GRAPH_UNITS) results
> in a kernel NULL pointer dereference, causing a crash when userspace
> (GNOME/Mesa) attempts to probe the device.
>
> Add safety checks for 'gr', 'gr->func', and 'nvkm_device->func' in the
> ioctl handler. Return -ENODEV to signal the missing hardware state to
> userspace, and use NV_ERROR_ONCE to provide diagnostic proof in the
> kernel log without risking a console flood.
>
> NOTE:
>
> I encountered these crashes while booting unrelated code (in
> dynamic-debug) on real HW.  There was also some fwupd updates around
> this time, so it could all be transient/unreproducible.  But it did
> happen, and could happen again in unforseen circumstances.
>
> @Capitain_Jack tested the error path in v1 by deleting the FW
>
> Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
> Tested-by: Daniel Campos Ramos <Capitain_Jack@yahoo.com>

Do they need to be separate patches? Do we need a Fixes: tag? Why not CC stable?

> ---
>  drivers/gpu/drm/nouveau/nouveau_abi16.c | 22 ++++++++++++++++++++--
>  1 file changed, 20 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/nouveau/nouveau_abi16.c b/drivers/gpu/drm/nouveau/nouveau_abi16.c
> index 4542d5f4ded8..3f130cd4fbcd 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_abi16.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_abi16.c
> @@ -306,6 +306,11 @@ nouveau_abi16_ioctl_getparam(ABI16_IOCTL_ARGS)
>  		getparam->value = 1;
>  		break;
>  	case NOUVEAU_GETPARAM_GRAPH_UNITS:
> +		if (!gr || !gr->func) {
> +			NV_ERROR_ONCE(drm, "GETPARAM_GRAPH_UNITS: no gr engine or func\n");
> +			return -ENODEV;
> +		}
> +
>  		getparam->value = nvkm_gr_units(gr);
>  		break;
>  	case NOUVEAU_GETPARAM_EXEC_PUSH_MAX: {
> @@ -315,10 +320,23 @@ nouveau_abi16_ioctl_getparam(ABI16_IOCTL_ARGS)
>  		break;
>  	}
>  	case NOUVEAU_GETPARAM_VRAM_BAR_SIZE:
> -		getparam->value = nvkm_device->func->resource_size(nvkm_device, NVKM_BAR1_FB);
> +		if (!nvkm_device || !nvkm_device->func || !nvkm_device->func->resource_size) {

How can any of those ever be NULL?

> +			NV_ERROR_ONCE(drm, "GETPARAM_VRAM_BAR_SIZE: no device func\n");
> +			return -ENODEV;
> +		}
> +
> +		getparam->value =
> +			nvkm_device->func->resource_size(nvkm_device, NVKM_BAR1_FB);
>  		break;
>  	case NOUVEAU_GETPARAM_VRAM_USED: {
> -		struct ttm_resource_manager *vram_mgr = ttm_manager_type(&drm->ttm.bdev, TTM_PL_VRAM);
> +		struct ttm_resource_manager *vram_mgr =
> +			ttm_manager_type(&drm->ttm.bdev, TTM_PL_VRAM);
> +
> +		if (!vram_mgr) {

Same here, how can this ever be NULL?

> +			NV_ERROR_ONCE(drm, "GETPARAM_VRAM_USED: no vram mgr\n");
> +			return -ENODEV;
> +		}
> +
>  		getparam->value = (u64)ttm_resource_manager_usage(vram_mgr);
>  		break;
>  	}
>
> -- 
> 2.56.0