Re: [PATCH 62/64] netlink: Avoid false-positive memcpy() warning

[Greg Kroah-Hartman]

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@xxxxxxxxxxxx>
> ---
>  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