From 98b3828351a135e6a1e9cf51501e704c8a5e1d6e Mon Sep 17 00:00:00 2001 From: Avery Pennarun Date: Wed, 6 Nov 2019 00:28:02 -0800 Subject: tun: NetlinkListener: don't send EventDown before sending EventUp This works around a startup race condition when competing with HackListener, which is trying to do the same job. If HackListener detects that the tundev is running while there is still an event in the netlink queue that says it isn't running, then the device receives a string of events like EventUp (HackListener) EventDown (NetlinkListener) EventUp (NetlinkListener) Unfortunately, after the first EventDown, the device stops itself, thinking incorrectly that the administrator has downed its tundev. The device is ignoring the initial EventDown anyway, so just don't emit it. Signed-off-by: Avery Pennarun --- tun/tun_linux.go | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-) diff --git a/tun/tun_linux.go b/tun/tun_linux.go index 2f97ebb..1e44b59 100644 --- a/tun/tun_linux.go +++ b/tun/tun_linux.go @@ -66,14 +66,19 @@ func (tun *NativeTun) routineHackListener() { } switch err { case unix.EINVAL: + // If the tunnel is up, it reports that write() is + // allowed but we provided invalid data. tun.events <- EventUp case unix.EIO: + // If the tunnel is down, it reports that no I/O + // is possible, without checking our provided data. tun.events <- EventDown default: return } select { case <-time.After(time.Second): + // nothing case <-tun.statusListenersShutdown: return } @@ -128,6 +133,7 @@ func (tun *NativeTun) routineNetlinkListener() { default: } + wasEverUp := false for remain := msg[:msgn]; len(remain) >= unix.SizeofNlMsghdr; { hdr := *(*unix.NlMsghdr)(unsafe.Pointer(&remain[0])) @@ -151,10 +157,16 @@ func (tun *NativeTun) routineNetlinkListener() { if info.Flags&unix.IFF_RUNNING != 0 { tun.events <- EventUp + wasEverUp = true } if info.Flags&unix.IFF_RUNNING == 0 { - tun.events <- EventDown + // Don't emit EventDown before we've ever emitted EventUp. + // This avoids a startup race with HackListener, which + // might detect Up before we have finished reporting Down. + if wasEverUp { + tun.events <- EventDown + } } tun.events <- EventMTUUpdate -- cgit v1.2.3-54-g00ecf