From mboxrd@z Thu Jan  1 00:00:00 1970
From: Christoph Hellwig <hch@infradead.org>
Subject: Re: [RFC][PATCH] get rid of the use of set_fs() (by way of
 kernel_recvmsg()) in sunrpc
Date: Thu, 18 Jan 2018 08:29:57 -0800
Message-ID: <20180118162957.GA16649@infradead.org>
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Cc: Linus Torvalds <torvalds@linux-foundation.org>,
        Network Development <netdev@vger.kernel.org>,
        Dan Williams <dan.j.williams@intel.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
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        Kees Cook <keescook@chromium.org>,
        kernel-hardening@lists.openwall.com,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        the arch/x86 maintainers <x86@kernel.org>,
        Ingo Molnar <mingo@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Andrew Morton <akpm@linux-foundation.org>,
        Alan Cox <alan@linux.intel.com>,
        David Miller <davem@davemloft.net>
To: Al Viro <viro@ZenIV.linux.org.uk>
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> 	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.