netdev - Re: [RFC][PATCH] get rid of the use of set_fs() (by way of kernel

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Date:   Thu, 18 Jan 2018 08:29:57 -0800
From:   Christoph Hellwig <hch@...radead.org>
To:     Al Viro <viro@...IV.linux.org.uk>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Network Development <netdev@...r.kernel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arch@...r.kernel.org, Andi Kleen <ak@...ux.intel.com>,
        Kees Cook <keescook@...omium.org>,
        kernel-hardening@...ts.openwall.com,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alan Cox <alan@...ux.intel.com>,
        David Miller <davem@...emloft.net>
Subject: Re: [RFC][PATCH] get rid of the use of set_fs() (by way of
 kernel_recvmsg()) in sunrpc

> 	We could turn ->msg_control/->msg_controllen into another
> iov_iter, but seeing that we never do scatter-gather for those
> IMO that would be a massive overkill.  A flag controlling whether
> ->msg_control is kernel or userland pointer would do, especially
> since we already have a flag for "do we want a native or compat
> layout for cmsg" in there.

While your current hack seems like a nice short term improvement
I think we need an iov_iter or iov_iter-light there in the long run.
Same for ioctl so that we can pass properly typed kernel or user
buffers through without all these set_fs hacks.