[PATCH] virt: vbox: struct vmmdev_hgcm_pagelist: Replace 1-element array with flexible array

[PATCH] virt: vbox: struct vmmdev_hgcm_pagelist: Replace 1-element array with flexible array

[Kees Cook]

Replace the deprecated[1] use of a 1-element array in
struct vmmdev_hgcm_pagelist with a modern flexible array. As this is
UAPI, we cannot trivially change the size of the struct, so use a union
to retain the old first element's size, but switch "pages" to a flexible
array.

No binary differences are present after this conversion.

Link: https://github.com/KSPP/linux/issues/79 [1]
Signed-off-by: Kees Cook <kees@kernel.org>
---
Cc: Hans de Goede <hdegoede@redhat.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: "Gustavo A. R. Silva" <gustavoars@kernel.org>
Cc: linux-hardening@vger.kernel.org
---
 include/uapi/linux/vbox_vmmdev_types.h | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/include/uapi/linux/vbox_vmmdev_types.h b/include/uapi/linux/vbox_vmmdev_types.h
index f8a8d6b3c521..6073858d52a2 100644
--- a/include/uapi/linux/vbox_vmmdev_types.h
+++ b/include/uapi/linux/vbox_vmmdev_types.h
@@ -282,7 +282,10 @@ struct vmmdev_hgcm_pagelist {
 	__u32 flags;             /** VMMDEV_HGCM_F_PARM_*. */
 	__u16 offset_first_page; /** Data offset in the first page. */
 	__u16 page_count;        /** Number of pages. */
-	__u64 pages[1];          /** Page addresses. */
+	union {
+		__u64 unused;	/** Deprecated place-holder for first "pages" entry. */
+		__DECLARE_FLEX_ARRAY(__u64, pages); /** Page addresses. */
+	};
 };
 VMMDEV_ASSERT_SIZE(vmmdev_hgcm_pagelist, 4 + 2 + 2 + 8);
 
-- 
2.34.1

Re: [PATCH] virt: vbox: struct vmmdev_hgcm_pagelist: Replace 1-element array with flexible array

[Gustavo A. R. Silva]

On 10/07/24 17:15, Kees Cook wrote:
> Replace the deprecated[1] use of a 1-element array in
> struct vmmdev_hgcm_pagelist with a modern flexible array. As this is
> UAPI, we cannot trivially change the size of the struct, so use a union
> to retain the old first element's size, but switch "pages" to a flexible
> array.
> 
> No binary differences are present after this conversion.
> 
> Link: https://github.com/KSPP/linux/issues/79 [1]
> Signed-off-by: Kees Cook <kees@kernel.org>
> ---
> Cc: Hans de Goede <hdegoede@redhat.com>
> Cc: Arnd Bergmann <arnd@arndb.de>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: "Gustavo A. R. Silva" <gustavoars@kernel.org>
> Cc: linux-hardening@vger.kernel.org

Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>

Thanks
--
Gustavo

> ---
>   include/uapi/linux/vbox_vmmdev_types.h | 5 ++++-
>   1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/include/uapi/linux/vbox_vmmdev_types.h b/include/uapi/linux/vbox_vmmdev_types.h
> index f8a8d6b3c521..6073858d52a2 100644
> --- a/include/uapi/linux/vbox_vmmdev_types.h
> +++ b/include/uapi/linux/vbox_vmmdev_types.h
> @@ -282,7 +282,10 @@ struct vmmdev_hgcm_pagelist {
>   	__u32 flags;             /** VMMDEV_HGCM_F_PARM_*. */
>   	__u16 offset_first_page; /** Data offset in the first page. */
>   	__u16 page_count;        /** Number of pages. */
> -	__u64 pages[1];          /** Page addresses. */
> +	union {
> +		__u64 unused;	/** Deprecated place-holder for first "pages" entry. */
> +		__DECLARE_FLEX_ARRAY(__u64, pages); /** Page addresses. */
> +	};
>   };
>   VMMDEV_ASSERT_SIZE(vmmdev_hgcm_pagelist, 4 + 2 + 2 + 8);
>   

Re: [PATCH] virt: vbox: struct vmmdev_hgcm_pagelist: Replace 1-element array with flexible array

[Kees Cook]

On Wed, 10 Jul 2024 16:15:55 -0700, Kees Cook wrote:
> Replace the deprecated[1] use of a 1-element array in
> struct vmmdev_hgcm_pagelist with a modern flexible array. As this is
> UAPI, we cannot trivially change the size of the struct, so use a union
> to retain the old first element's size, but switch "pages" to a flexible
> array.
> 
> No binary differences are present after this conversion.
> 
> [...]

Applied to for-next/hardening, thanks!

[1/1] virt: vbox: struct vmmdev_hgcm_pagelist: Replace 1-element array with flexible array
      https://git.kernel.org/kees/c/5ac86f0ed04b

Take care,

-- 
Kees Cook