Thanks
> -----Original Message-----
> From: David Miller [mailto:da...@davemloft.net]
> Sent: Thursday, January 05, 2017 2:25 AM
> To: cug...@163.com
> Cc: netdev@vger.kernel.org; YUAN Linyu
> Subject: Re: [PATCH] scm: remove use CMSG{_COMPAT}_ALIGN(sizeof(struct
> {compat_}cmsghdr))
>
> From: yuan linyu <cug...@163.com>
> Date: Tue, 3 Jan 2017 20:42:17 +0800
>
> > From: yuan linyu <linyu.y...@alcatel-sbell.com.cn>
> >
> > sizeof(struct cmsghdr) and sizeof(struct compat_cmsghdr) already aligned.
> > remove use CMSG_ALIGN(sizeof(struct cmsghdr)) and
> > CMSG_COMPAT_ALIGN(sizeof(struct compat_cmsghdr)) keep code
> consistent.
> >
> > Signed-off-by: yuan linyu <linyu.y...@alcatel-sbell.com.cn>
>
> Applied, and I added the following commit which will make sure our
> analysis is accurate.
>
> ====================
> [PATCH] net: Assert at build time the assumptions we make about the CMSG
> header.
>
> It must always be the case that CMSG_ALIGN(sizeof(hdr)) == sizeof(hdr).
>
> Otherwise there are missing adjustments in the various calculations
> that parse and build these things.
>
> Signed-off-by: David S. Miller <da...@davemloft.net>
> ---
> net/compat.c | 3 +++
> net/socket.c | 2 ++
> 2 files changed, 5 insertions(+)
>
> diff --git a/net/compat.c b/net/compat.c
> index 4e27dd1..ba3ac72 100644
> --- a/net/compat.c
> +++ b/net/compat.c
> @@ -130,6 +130,9 @@ int cmsghdr_from_user_compat_to_kern(struct
> msghdr *kmsg, struct sock *sk,
> __kernel_size_t kcmlen, tmp;
> int err = -EFAULT;
>
> + BUILD_BUG_ON(sizeof(struct compat_cmsghdr) !=
> + CMSG_COMPAT_ALIGN(sizeof(struct compat_cmsghdr)));
> +
> kcmlen = 0;
> kcmsg_base = kcmsg = (struct cmsghdr *)stackbuf;
> ucmsg = CMSG_COMPAT_FIRSTHDR(kmsg);
> diff --git a/net/socket.c b/net/socket.c
> index 8487bf1..5f3b5a2 100644
> --- a/net/socket.c
> +++ b/net/socket.c
> @@ -1948,6 +1948,8 @@ static int ___sys_sendmsg(struct socket *sock,
> struct user_msghdr __user *msg,
> ctl_buf = msg_sys->msg_control;
> ctl_len = msg_sys->msg_controllen;
> } else if (ctl_len) {
> + BUILD_BUG_ON(sizeof(struct cmsghdr) !=
> + CMSG_ALIGN(sizeof(struct cmsghdr)));
> if (ctl_len > sizeof(ctl)) {
> ctl_buf = sock_kmalloc(sock->sk, ctl_len, GFP_KERNEL);
> if (ctl_buf == NULL)
> --
> 2.4.11
