[Openvpn-devel] Workaround FreeBSD 12+ race condition on tun/tap open with IPv6.

Message ID 20200722132852.48508-1-gert@greenie.muc.de
State Superseded
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Series
  • [Openvpn-devel] Workaround FreeBSD 12+ race condition on tun/tap open with IPv6.
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Commit Message

Gert Doering July 22, 2020, 1:28 p.m.
On FreeBSD 12 (tested and verified on 12.1-RELEASE-p2), after "ifconfig
inet6" for a tun/tap interface, there sometimes is a race condition
where the "IFDISABLED" flag shows up after a short time frame, under
a second, and never clears itself.  This disables use of the configured
IPv6 address on the interface, breaking IPv6 over tun/tap operation.

As a workaround until this can be fixed on the FreeBSD side (or a
better workaround is found), sleep(1) after ifconfig, then call
"ifconfig $dev inet6 -ifdisable".

Yes, this is massively ugly but makes the problem completely go
away for my test systems.

(The same effect can be achieved with an --up script that does this,
but it's even less pretty - see trac ticket)

Trac: 1226
Signed-off-by: Gert Doering <gert@greenie.muc.de>
---
 src/openvpn/tun.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

Patch

diff --git a/src/openvpn/tun.c b/src/openvpn/tun.c
index e96368ca..2d3ba623 100644
--- a/src/openvpn/tun.c
+++ b/src/openvpn/tun.c
@@ -1038,6 +1038,23 @@  do_ifconfig_ipv6(struct tuntap *tt, const char *ifname, int tun_mtu,
     openvpn_execve_check(&argv, es, S_FATAL,
                          "generic BSD ifconfig inet6 failed");
 
+#if defined(TARGET_FREEBSD) && __FreeBSD_version >= 1200000
+    /* FreeBSD 12 grew some sort of race condition where sometimes
+     * the IPv6 side of a tun interface is stuck in "IFDISABLED"
+     * in "ifconfig tun0" output, and the assigned IPv6 address is not
+     * working ("tentative").  Workaround in here, for now.
+     *
+     * the sleep is needed because there is a race condition, so turning
+     * it off immediately can lead to "kernel turns it on again, stuck!!"
+     */
+    sleep(1);
+    argv_printf(&argv, "%s %s inet6 -ifdisabled", IFCONFIG_PATH, ifname);
+    argv_msg(M_INFO, &argv);
+
+    openvpn_execve_check(&argv, es, S_FATAL,
+                         "FreeBSD BSD 'ifconfig inet6 -ifdisabled' failed");
+#endif
+
 #if defined(TARGET_OPENBSD) || defined(TARGET_NETBSD) \
     || defined(TARGET_DARWIN)
     /* and, hooray, we explicitly need to add a route... */