Re: [PATCH] drm/nouveau/acr: Fix undefined behavior in nvkm_acr_hsfw_load_bl()

[Lyude Paul <lyude@redhat.com>]

Reviewed-by: Lyude Paul <lyude@redhat.com>

On Tue, 2022-01-25 at 00:58 +0800, Zhou Qingyang wrote:
> In nvkm_acr_hsfw_load_bl(), the return value of kmalloc() is directly
> passed to memcpy(), which could lead to undefined behavior on failure
> of kmalloc().
> 
> Fix this bug by using kmemdup() instead of kmalloc()+memcpy().
> 
> This bug was found by a static analyzer.
> 
> Builds with 'make allyesconfig' show no new warnings,
> and our static analyzer no longer warns about this code.
> 
> Fixes: 22dcda45a3d1 ("drm/nouveau/acr: implement new subdev to replace
> "secure boot"")
> Signed-off-by: Zhou Qingyang <zhou1615@umn.edu>
> ---
> The analysis employs differential checking to identify inconsistent 
> security operations (e.g., checks or kfrees) between two code paths 
> and confirms that the inconsistent operations are not recovered in the
> current function or the callers, so they constitute bugs. 
> 
> Note that, as a bug found by static analysis, it can be a false
> positive or hard to trigger. Multiple researchers have cross-reviewed
> the bug.
> 
>  drivers/gpu/drm/nouveau/nvkm/subdev/acr/hsfw.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/nouveau/nvkm/subdev/acr/hsfw.c
> b/drivers/gpu/drm/nouveau/nvkm/subdev/acr/hsfw.c
> index 667fa016496e..a6ea89a5d51a 100644
> --- a/drivers/gpu/drm/nouveau/nvkm/subdev/acr/hsfw.c
> +++ b/drivers/gpu/drm/nouveau/nvkm/subdev/acr/hsfw.c
> @@ -142,11 +142,12 @@ nvkm_acr_hsfw_load_bl(struct nvkm_acr *acr, const char
> *name, int ver,
>  
>         hsfw->imem_size = desc->code_size;
>         hsfw->imem_tag = desc->start_tag;
> -       hsfw->imem = kmalloc(desc->code_size, GFP_KERNEL);
> -       memcpy(hsfw->imem, data + desc->code_off, desc->code_size);
> -
> +       hsfw->imem = kmemdup(data + desc->code_off, desc->code_size,
> GFP_KERNEL);
>         nvkm_firmware_put(fw);
> -       return 0;
> +       if (!hsfw->imem)
> +               return -ENOMEM;
> +       else
> +               return 0;
>  }
>  
>  int

-- 
Cheers,
 Lyude Paul (she/her)
 Software Engineer at Red Hat