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

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 <[email protected]>

---
Cc: Hans de Goede <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Cc: "Gustavo A. R. Silva" <[email protected]>
Cc: [email protected]

---
  include/uapi/linux/vbox_vmmdev_types.h | 5 ++++-
  1 file changed, 4 insertions(+), 1 deletion(-)

include/uapi/linux/vbox_vmmdev_types.h +4 -1

index f8a8d6b3c521..6073858d52a2 100644
@@ -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);
 

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.

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