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Date:   Wed, 28 Jul 2021 07:49:46 +0200
From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     Kees Cook <keescook@chromium.org>
Cc:     linux-hardening@vger.kernel.org,
        "Gustavo A. R. Silva" <gustavoars@kernel.org>,
        Keith Packard <keithpac@amazon.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        linux-kernel@vger.kernel.org, linux-wireless@vger.kernel.org,
        netdev@vger.kernel.org, dri-devel@lists.freedesktop.org,
        linux-staging@lists.linux.dev, linux-block@vger.kernel.org,
        linux-kbuild@vger.kernel.org, clang-built-linux@googlegroups.com
Subject: Re: [PATCH 62/64] netlink: Avoid false-positive memcpy() warning
Message-ID: <YQDv+oG7ok0T1L+r@kroah.com>
References: <20210727205855.411487-1-keescook@chromium.org>
 <20210727205855.411487-63-keescook@chromium.org>
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On Tue, Jul 27, 2021 at 01:58:53PM -0700, Kees Cook wrote:
> In preparation for FORTIFY_SOURCE performing compile-time and run-time
> field bounds checking for memcpy(), memmove(), and memset(), avoid
> intentionally writing across neighboring fields.
> 
> Add a flexible array member to mark the end of struct nlmsghdr, and
> split the memcpy() to avoid false positive memcpy() warning:
> 
> memcpy: detected field-spanning write (size 32) of single field (size 16)
> 
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
>  include/uapi/linux/netlink.h | 1 +
>  net/netlink/af_netlink.c     | 4 +++-
>  2 files changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/include/uapi/linux/netlink.h b/include/uapi/linux/netlink.h
> index 4c0cde075c27..ddeaa748df5e 100644
> --- a/include/uapi/linux/netlink.h
> +++ b/include/uapi/linux/netlink.h
> @@ -47,6 +47,7 @@ struct nlmsghdr {
>  	__u16		nlmsg_flags;	/* Additional flags */
>  	__u32		nlmsg_seq;	/* Sequence number */
>  	__u32		nlmsg_pid;	/* Sending process port ID */
> +	__u8		contents[];

Is this ok to change a public, userspace visable, structure?

Nothing breaks?

thanks,

greg k-h