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

Greg Kroah-Hartman
2021-07-28T05:49:51Z

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