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

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Message-Id: <20240710231555.work.406-kees@kernel.org>
Date: Wed, 10 Jul 2024 16:15:55 -0700
From: Kees Cook <kees@...nel.org>
To: Hans de Goede <hdegoede@...hat.com>
Cc: Kees Cook <kees@...nel.org>,
	Arnd Bergmann <arnd@...db.de>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"Gustavo A. R. Silva" <gustavoars@...nel.org>,
	linux-hardening@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] 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 <kees@...nel.org>
---
Cc: Hans de Goede <hdegoede@...hat.com>
Cc: Arnd Bergmann <arnd@...db.de>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc: linux-hardening@...r.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