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Date:   Wed, 19 Jul 2023 08:36:53 -0700
From:   Kees Cook <keescook@chromium.org>
To:     Larry Finger <Larry.Finger@lwfinger.net>
Cc:     Hans de Goede <hdegoede@redhat.com>,
        Azeem Shaikh <azeemshaikh38@gmail.com>,
        LKML <linux-kernel@vger.kernel.org>,
        linux-hardening@vger.kernel.org,
        "Gustavo A. R. Silva" <gustavoars@kernel.org>
Subject: Re: Crash in VirtualBox virtual machines running kernel 6.5
Message-ID: <202307190835.752D710D@keescook>
References: <ab3a70e9-60ed-0f13-e3d4-8866eaccc8c1@lwfinger.net>
 <202307190823.086EFD42D9@keescook>
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Okay, please try:

diff --git a/fs/vboxsf/shfl_hostintf.h b/fs/vboxsf/shfl_hostintf.h
index aca829062c12..902fe3224453 100644
--- a/fs/vboxsf/shfl_hostintf.h
+++ b/fs/vboxsf/shfl_hostintf.h
@@ -68,12 +68,11 @@ struct shfl_string {
 
 	/** UTF-8 or UTF-16 string. Nul terminated. */
 	union {
-		u8 utf8[2];
-		u16 utf16[1];
-		u16 ucs2[1]; /* misnomer, use utf16. */
+		DECLARE_FLEX_ARRAY(u8, utf8);
+		DECLARE_FLEX_ARRAY(u16, utf16);
 	} string;
 };
-VMMDEV_ASSERT_SIZE(shfl_string, 6);
+VMMDEV_ASSERT_SIZE(shfl_string, 4);
 
 /* The size of shfl_string w/o the string part. */
 #define SHFLSTRING_HEADER_SIZE  4


The size assert doesn't seem to be used anywhere else, but I can do a
more careful binary analysis later today...

-- 
Kees Cook