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Workaround FreeBSD 12+ race condition on tun/tap open with IPv6.

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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.

This only happens if ipv6_activate_all_interfaces="YES" is not
set in /etc/rc.conf - but there might be reasons why this is not so.

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)

FreeBSD: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=248172

v2: reword text, refer to FreeBSD bug with much more details

Trac: 1226
Signed-off-by: Gert Doering <gert@greenie.muc.de>
Acked-by: Arne Schwabe <arne@rfc2549.org>
Message-Id: <20200723121949.78223-1-gert@greenie.muc.de>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg20553.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>
This commit is contained in:
Gert Doering 2020-07-23 14:19:49 +02:00
parent 10abd656a3
commit 5e19cc2c1b
1 changed files with 23 additions and 0 deletions
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23
src/openvpn/tun.c
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@ -1038,6 +1038,29 @@ 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
/* On FreeBSD 12 and up, there is ipv6_activate_all_interfaces="YES"
* in rc.conf, which is not set by default. If it is *not* set,
* "all new interfaces that are not already up" are configured by
* devd + /etc/pccard_ether as "inet6 ifdisabled".
*
* The "is this interface already up?" test is a non-zero time window
* which we manage to hit with our ifconfig often enough to cause
* frequent fails in the openvpn test environment.
*
* Thus: assume that the system might interfere, wait for things to
* settle (it's a very short time window), and remove -ifdisable again.
*
* See: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=248172
*/
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... */