[PATCH] drm/nouveau/mmu: fix Use after Free bug in nvkm_vmm_node_split

[Takashi Iwai]

On Fri, 30 Dec 2022 08:27:58 +0100,
Zheng Wang wrote:
> 
> Here is a function call chain.
> nvkm_vmm_pfn_map->nvkm_vmm_pfn_split_merge->nvkm_vmm_node_split
> If nvkm_vma_tail return NULL in nvkm_vmm_node_split, it will
> finally invoke nvkm_vmm_node_merge->nvkm_vmm_node_delete, which
> will free the vma. However, nvkm_vmm_pfn_map didn't notice that.
> It goes into next label and UAF happens.
> 
> Fix it by returning the return-value of nvkm_vmm_node_merge
> instead of NULL.
> 
> Signed-off-by: Zheng Wang <zyytlz.wz at 163.com>

FWIW, CVE-2023-0030 has been assigned to this bug.
It's a question whether it really deserves as a security issue, but a
bug is a bug...

Ben, could you review this please?


thanks,

Takashi

> ---
>  drivers/gpu/drm/nouveau/nvkm/subdev/mmu/vmm.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/nouveau/nvkm/subdev/mmu/vmm.c b/drivers/gpu/drm/nouveau/nvkm/subdev/mmu/vmm.c
> index ae793f400ba1..84d6fc87b2e8 100644
> --- a/drivers/gpu/drm/nouveau/nvkm/subdev/mmu/vmm.c
> +++ b/drivers/gpu/drm/nouveau/nvkm/subdev/mmu/vmm.c
> @@ -937,8 +937,8 @@ nvkm_vmm_node_split(struct nvkm_vmm *vmm,
>  	if (vma->size != size) {
>  		struct nvkm_vma *tmp;
>  		if (!(tmp = nvkm_vma_tail(vma, vma->size - size))) {
> -			nvkm_vmm_node_merge(vmm, prev, vma, NULL, vma->size);
> -			return NULL;
> +			tmp = nvkm_vmm_node_merge(vmm, prev, vma, NULL, vma->size);
> +			return tmp;
>  		}
>  		tmp->part = true;
>  		nvkm_vmm_node_insert(vmm, tmp);
> -- 
> 2.25.1
>