netdev - RE: [PATCH 15/17] switch kernel_sendmsg() and kernel_recvmsg() to iov_iter

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Message-ID: <063D6719AE5E284EB5DD2968C1650D6D1CB1DD9D@AcuExch.aculab.com>
Date:	Tue, 14 Apr 2015 16:21:02 +0000
From:	David Laight <David.Laight@...LAB.COM>
To:	'Al Viro' <viro@...IV.linux.org.uk>,
	"davem@...emloft.net" <davem@...emloft.net>
CC:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: RE: [PATCH 15/17] switch kernel_sendmsg() and kernel_recvmsg() to
 iov_iter_kvec()

From: Al Viro
> Sent: 11 April 2015 22:18
> From: Al Viro <viro@...iv.linux.org.uk>
> 
> For kernel_sendmsg() that eliminates the need to play with setfs();
> for kernel_recvmsg() it does *not* - a couple of callers are using
> it with non-NULL ->msg_control, which would be treated as userland
> address on recvmsg side of things.
> 
> In all cases we are really setting a kvec-backed iov_iter, though.
> 
> Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
> ---
>  net/socket.c | 20 +++-----------------
>  1 file changed, 3 insertions(+), 17 deletions(-)
> 
> diff --git a/net/socket.c b/net/socket.c
> index e5669ce..b6ceeda 100644
> --- a/net/socket.c
> +++ b/net/socket.c
> @@ -627,18 +627,8 @@ EXPORT_SYMBOL(sock_sendmsg);
>  int kernel_sendmsg(struct socket *sock, struct msghdr *msg,
>  		   struct kvec *vec, size_t num, size_t size)
>  {
> -	mm_segment_t oldfs = get_fs();
> -	int result;
> -
> -	set_fs(KERNEL_DS);
> -	/*
> -	 * the following is safe, since for compiler definitions of kvec and
> -	 * iovec are identical, yielding the same in-core layout and alignment
> -	 */
> -	iov_iter_init(&msg->msg_iter, WRITE, (struct iovec *)vec, num, size);
> -	result = sock_sendmsg(sock, msg, size);
> -	set_fs(oldfs);
> -	return result;
> +	iov_iter_kvec(&msg->msg_iter, WRITE | ITER_KVEC, vec, num, size);
> +	return sock_sendmsg(sock, msg, size);

Massive NAK.
This breaks any code that is using msg_control to set SCTP parameters
when sending data.

	David

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