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

[Takashi Iwai <tiwai@suse.de>]

On Tue, 03 Jan 2023 15:07:55 +0100,
Takashi Iwai wrote:
> 
> 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@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?

A gentle ping as reminder.  The bug is still present.


thanks,

Takashi

> 
> 
> 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
> >