[gentoo-portage-dev] [PATCH] Configure a dummy network interface for network-sandbox

[Mike Gilbert <floppym@gentoo.org>]

This works around some strange behavior in glibc's getaddrinfo()
implementation when the AI_ADDRCONFIG flag is set.

For example:

  struct addrinfo *res, hints = { .ai_family = AF_INET, .ai_flags = AI_ADDRCONFIG };
  getaddrinfo("localhost", NULL, &hints, &res);

This returns no results if there is no non-loopback interface configured with an
IPv4 address.

Bug: https://bugs.gentoo.org/690758
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=12377#c13
Signed-off-by: Mike Gilbert <floppym@gentoo.org>
---
 lib/portage/process.py | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/lib/portage/process.py b/lib/portage/process.py
index dfbda75de..c284c04f3 100644
--- a/lib/portage/process.py
+++ b/lib/portage/process.py
@@ -446,6 +446,29 @@ def spawn(mycommand, env=None, opt_name=None, fd_pipes=None, returnpid=False,
 	# Everything succeeded
 	return 0
 
+def _configure_dummy_interface():
+	"""
+	Configure a dummy interface to work around odd behavior in glibc's
+	getaddrinfo() implementation when the AI_ADDRCONFIG flag is set.
+
+	For example:
+
+	  struct addrinfo *res, hints = { .ai_family = AF_INET, .ai_flags = AI_ADDRCONFIG };
+	  getaddrinfo("localhost", NULL, &hints, &res);
+
+	This returns no results if there is no non-loopback interface configured with an
+	IPv4 address.
+
+	Bug: https://bugs.gentoo.org/690758
+	Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=12377#c13
+	"""
+	try:
+		subprocess.check_call(['ip','link','add','dummy','type','dummy'])
+		subprocess.check_call(['ip','link','set','dummy','up'])
+		subprocess.check_call(['ip','address','add','10.0.0.1/8','dev','dummy'])
+	except subprocess.CalledProcessError:
+		writemsg("Unable to configure dummy network interface\n")
+
 def _exec(binary, mycommand, opt_name, fd_pipes,
 	env, gid, groups, uid, umask, cwd,
 	pre_exec, close_fds, unshare_net, unshare_ipc, unshare_mount, unshare_pid,
@@ -637,6 +660,7 @@ def _exec(binary, mycommand, opt_name, fd_pipes,
 									errno.errorcode.get(e.errno, '?')),
 									noiselevel=-1)
 							sock.close()
+							_configure_dummy_interface()
 				except AttributeError:
 					# unshare() not supported by libc
 					pass
-- 
2.22.0