Re: [PATCH 2/2] nouveau/dmem: Fix memory leak in `migrate_to_ram` upon copy error

[Danilo Krummrich <dakr@kernel.org>]

On Mon, Sep 23, 2024 at 01:54:58PM +0000, Yonatan Maman wrote:
> A copy push command might fail, causing `migrate_to_ram` to return a
> dirty HIGH_USER page to the user.
> 
> This exposes a security vulnerability in the nouveau driver. To prevent
> memory leaks in `migrate_to_ram` upon a copy error, allocate a zero
> page for the destination page.

So, you refer to the case where this function fails in nouveau_dmem_copy_one()?

If so, can you please explain why adding __GFP_ZERO to alloc_page_vma() helps
with that?

> 
> Signed-off-by: Yonatan Maman <Ymaman@Nvidia.com>
> Signed-off-by: Gal Shalom <GalShalom@Nvidia.com>

Since this is a bug, please also add a 'Fixes' tag, CC stable and add a
'Co-developed-by' tag if appropriate.

> ---
>  drivers/gpu/drm/nouveau/nouveau_dmem.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/nouveau/nouveau_dmem.c b/drivers/gpu/drm/nouveau/nouveau_dmem.c
> index 6fb65b01d778..097bd3af0719 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_dmem.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_dmem.c
> @@ -193,7 +193,7 @@ static vm_fault_t nouveau_dmem_migrate_to_ram(struct vm_fault *vmf)
>  	if (!spage || !(src & MIGRATE_PFN_MIGRATE))
>  		goto done;
>  
> -	dpage = alloc_page_vma(GFP_HIGHUSER, vmf->vma, vmf->address);
> +	dpage = alloc_page_vma(GFP_HIGHUSER | __GFP_ZERO, vmf->vma, vmf->address);
>  	if (!dpage)
>  		goto done;
>  
> -- 
> 2.34.1
>