From a8866ff6a5bce7d0ec465a63bc482a85c09b0d39 Mon Sep 17 00:00:00 2001
From: Al Viro <viro@zeniv.linux.org.uk>
Date: Fri, 12 Dec 2014 23:02:36 -0500
Subject: [PATCH] netlink: make the check for "send from tx_ring" deterministic

As it is, zero msg_iovlen means that the first iovec in the kernel
array of iovecs is left uninitialized, so checking if its ->iov_base
is NULL is random.  Since the real users of that thing are doing
sendto(fd, NULL, 0, ...), they are getting msg_iovlen = 1 and
msg_iov[0] = {NULL, 0}, which is what this test is trying to catch.
As suggested by davem, let's just check that msg_iovlen was 1 and
msg_iov[0].iov_base was NULL - _that_ is well-defined and it catches
what we want to catch.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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