From mboxrd@z Thu Jan  1 00:00:00 1970
From: David Miller <davem@davemloft.net>
Subject: Re: [RFC] [PATCH] net: socket: Fix the wrong returns for recvmsg
 and sendmsg
Date: Mon, 01 Jun 2015 22:23:57 -0700 (PDT)
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From: Junling Zheng <zhengjunling@huawei.com>
Date: Tue, 2 Jun 2015 12:05:32 +0800

> So, the problem commit is 281c9c36 (net: compat: Update
> get_compat_msghdr() to match copy_msghdr_from_user() behaviour),
> which fixes db31c55a6fb2 and brings the get_compat_msghdr() in line
> with copy_msghdr_from_user().

Upstream this got fixed by:

08adb7dabd4874cc5666b4490653b26534702ce0

So the part that makes us not unconditionally return -EFAULT needs
to be backported, and that's probably equivalent to the patch
your proposed which therefore should be applied.