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 17:10:20 +0000
From:   Al Viro <viro@...IV.linux.org.uk>
To:     Christoph Hellwig <hch@...radead.org>
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

On Thu, Jan 18, 2018 at 08:29:57AM -0800, Christoph Hellwig wrote:
> > 	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.

For one caller in the entire history of the kernel?

> Same for ioctl so that we can pass properly typed kernel or user
> buffers through without all these set_fs hacks.

Umm...  Most of the PITA with ioctls is due to compat ones being
reformatted for native and fed under set_fs().  I actually have
a series dealing with most of such places for net ioctls.  Sure,
there's also ioctl_by_bdev(), but for those we might be better
off exposing the things like ->get_last_session() and its ilk to
filesystems that want to deal with cdroms...

It's kernel_setsockopt() that is the real PITA...