Re: [RFC][PATCH] get rid of the use of set_fs() (by way of kernel_recvmsg()) in sunrpc

[Al Viro]

On Thu, Jan 18, 2018 at 04:43:02AM +0000, Al Viro 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.
> 
> 	That's the only caller we need it for, but that thing looks cheap
> enough.  Obviously needs to pass testing, including "is it too ugly to
> live as far as Davem is concerned" test, though...

	BTW, there's another series of set_fs-removal patches in
net ioctls; still needs review, though.  With that one we would be down
to 11 instances in the entire net/*:

* SO_RCVTIMEO/SO_SNDTIMEO handling in compat [sg]etsockopt()
* passing SIOC{ADD,DEL}TUNNEL down (ipmr_del_tunnel(),ipmr_new_tunnel(),
  addrconf_set_dstaddr())
* SIOCGSTAMP/SIOCGSTAMPNS in compat ioctls
* SIOCADDRT/SIOCDELRT in compat ioctls
* kernel_[gs]etsockopt()
* ipv6_renew_options_kern()

I don't know if all of that stuff can be realistically done without set_fs().
kernel_setsockopt(), in particular, is unpleasant...

The patches need review and testing, obviously; I'll post them in followups,
the entire series (on top of net/master) is in
git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs.git #work.net-ioctl