Use RTNETLINK to configure the loopback interface

This eliminates the dependency on iproute2 on Linux.

Bug: https://bugs.gentoo.org/690758
Signed-off-by: Mike Gilbert <floppym@gentoo.org>
Signed-off-by: Zac Medico <zmedico@gentoo.org>

2 files changed, 108 insertions, 16 deletions

diff --git a/lib/portage/process.py b/lib/portage/process.py
index 2a2cbd972..df63ae72f 100644
--- a/lib/portage/process.py
+++ b/lib/portage/process.py
@@ -10,7 +10,6 @@ import multiprocessing
 import platform
 import signal
 import socket
-import struct
 import subprocess
 import sys
 import traceback
@@ -489,17 +488,6 @@ def _configure_loopback_interface():
 	Configure the loopback interface.
 	"""
 
-	IFF_UP = 0x1
-	ifreq = struct.pack('16sh', b'lo', IFF_UP)
-	SIOCSIFFLAGS = 0x8914
-
-	sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM, 0)
-	try:
-		fcntl.ioctl(sock, SIOCSIFFLAGS, ifreq)
-	except IOError as e:
-		writemsg("Unable to enable loopback interface: %s\n" % e.strerror, noiselevel=-1)
-	sock.close()
-
 	# We add some additional addresses to work around odd behavior in glibc's
 	# getaddrinfo() implementation when the AI_ADDRCONFIG flag is set.
 	#
@@ -514,12 +502,18 @@ def _configure_loopback_interface():
 	# Bug: https://bugs.gentoo.org/690758
 	# Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=12377#c13
 
+	# Avoid importing this module on systems that may not support netlink sockets.
+	from portage.util.netlink import RtNetlink
+
 	try:
-		subprocess.call(['ip', 'address', 'add', '10.0.0.1/8', 'dev', 'lo'])
-		if _has_ipv6():
-			subprocess.call(['ip', 'address', 'add', 'fd00::1/8', 'dev', 'lo'])
+		with RtNetlink() as rtnl:
+			ifindex = rtnl.get_link_ifindex(b'lo')
+			rtnl.set_link_up(ifindex)
+			rtnl.add_address(ifindex, socket.AF_INET, '10.0.0.1', 8)
+			if _has_ipv6():
+				rtnl.add_address(ifindex, socket.AF_INET6, 'fd::1', 8)
 	except EnvironmentError as e:
-		writemsg("Error calling 'ip': %s\n" % e.strerror, noiselevel=-1)
+		writemsg("Unable to configure loopback interface: %s\n" % e.strerror, noiselevel=-1)
 
 def _exec(binary, mycommand, opt_name, fd_pipes,
 	env, gid, groups, uid, umask, cwd,
diff --git a/lib/portage/util/netlink.py b/lib/portage/util/netlink.py
new file mode 100644
index 000000000..950ed8f69
--- /dev/null
+++ b/lib/portage/util/netlink.py
@@ -0,0 +1,98 @@
+# Copyright 2019 Gentoo Authors
+# Distributed under the terms of the GNU General Public License v2
+
+from io import BytesIO
+from os import strerror
+from struct import Struct
+
+import socket
+from socket import (
+	AF_NETLINK, AF_UNSPEC,
+	MSG_PEEK, MSG_TRUNC,
+	NETLINK_ROUTE,
+	SOCK_DGRAM,
+	inet_pton,
+)
+
+IFA_LOCAL = 2
+IFF_UP = 0x1
+IFLA_IFNAME = 3
+NLMSG_ERROR = 2
+RTM_NEWLINK = 16
+RTM_GETLINK = 18
+RTM_NEWADDR = 20
+NLM_F_REQUEST = 0x1
+NLM_F_ACK = 0x4
+NLM_F_EXCL = 0x200
+NLM_F_CREATE = 0x400
+
+nlmsghdr = Struct('=IHHII')
+nlmsgerr = Struct('i')
+rtattr = Struct('HH')
+ifinfomsg = Struct('BHiII')
+ifaddrmsg = Struct('BBBBi')
+
+def create_nlmsg(nlmsg_type, nlmsg_flags, nlmsg_seq, nlmsg_pid, data):
+	nlmsg_len = nlmsghdr.size + len(data)
+	return nlmsghdr.pack(nlmsg_len, nlmsg_type, nlmsg_flags, nlmsg_seq, nlmsg_pid) + data
+
+def create_rtattr(rta_type, data):
+	rta_len = rtattr.size + len(data)
+	return rtattr.pack(rta_len, rta_type) + data
+
+def parse_message(msg):
+	buf = BytesIO(msg)
+	hdr = nlmsghdr.unpack(buf.read(nlmsghdr.size))
+	if hdr[1] == NLMSG_ERROR:
+		err = nlmsgerr.unpack(buf.read(nlmsgerr.size))
+		error = -err[0]
+		if error != 0:
+			raise OSError(error, strerror(error))
+	elif hdr[1] == RTM_NEWLINK:
+		# kernel responds to RTM_GETLINK with RTM_NEWLINK.
+		# We only care about the ifindex for get_link_ifindex.
+		return ifinfomsg.unpack(buf.read(ifinfomsg.size))
+
+class RtNetlink:
+	def __init__(self):
+		self.sock = socket.socket(AF_NETLINK, SOCK_DGRAM, NETLINK_ROUTE)
+		self.addr = (0, 0)
+		try:
+			self.sock.bind(self.addr)
+		except socket.error:
+			self.sock.close()
+			raise
+
+	def __enter__(self):
+		return self
+
+	def __exit__(self, exc_type, exc_value, traceback):
+		self.sock.close()
+
+	def send_message(self, msg):
+		self.sock.sendto(msg, self.addr)
+		# Messages are variable length, but 128 is enough for the the ones we care about.
+		resp = self.sock.recv(128)
+		return parse_message(resp)
+
+	def get_link_ifindex(self, ifname):
+		body = ifinfomsg.pack(AF_UNSPEC, 0, 0, 0, 0)
+		body += create_rtattr(IFLA_IFNAME, ifname)
+		flags = NLM_F_REQUEST
+		msg = create_nlmsg(RTM_GETLINK, flags, 1, 0, body)
+		resp = self.send_message(msg)
+		return resp[2]
+
+	def set_link_up(self, ifindex):
+		body = ifinfomsg.pack(AF_UNSPEC, 0, ifindex, IFF_UP, IFF_UP)
+		flags = NLM_F_REQUEST|NLM_F_ACK
+		msg = create_nlmsg(RTM_NEWLINK, flags, 1, 0, body)
+		self.send_message(msg)
+
+	def add_address(self, ifindex, family, address, prefixlen):
+		body = ifaddrmsg.pack(family, prefixlen, 0, 0, ifindex)
+		addr = inet_pton(family, address)
+		body += create_rtattr(IFA_LOCAL, addr)
+		flags = NLM_F_REQUEST|NLM_F_ACK|NLM_F_EXCL|NLM_F_CREATE
+		msg = create_nlmsg(RTM_NEWADDR, flags, 1, 0, body)
+		self.send_message(msg)