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wgengine/monitor: subscribe to Linux ip rule events, log on rule deletes

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For debugging & working on #1591 where certain versions of systemd-networkd
delete Tailscale's ip rule entries.

Updates #1591

Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
This commit is contained in:
Brad Fitzpatrick 2021-07-18 14:50:47 -07:00
parent 14135dd935
commit 2ba36c294b
1 changed files with 20 additions and 1 deletions
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21
wgengine/monitor/monitor_linux.go
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@ -42,7 +42,9 @@ func newOSMon(logf logger.Logf, m *Mon) (osMon, error) {
// address as well to cover things like DHCP deciding to give
// us a new address upon renewal - routing wouldn't change,
// but all reachability would.
Groups: unix.RTMGRP_IPV4_IFADDR | unix.RTMGRP_IPV6_IFADDR | unix.RTMGRP_IPV4_ROUTE | unix.RTMGRP_IPV6_ROUTE,
Groups: unix.RTMGRP_IPV4_IFADDR | unix.RTMGRP_IPV6_IFADDR |
unix.RTMGRP_IPV4_ROUTE | unix.RTMGRP_IPV6_ROUTE |
unix.RTMGRP_IPV4_RULE, // no IPV6_RULE in x/sys/unix
})
if err != nil {
// Google Cloud Run does not implement NETLINK_ROUTE RTMGRP support
@ -117,6 +119,19 @@ func (c *nlConn) Receive() (message, error) {
Dst: dst,
Gateway: gw,
}, nil
case unix.RTM_DELRULE:
// For https://github.com/tailscale/tailscale/issues/1591 where
// systemd-networkd deletes our rules.
var rmsg rtnetlink.RouteMessage
err := rmsg.UnmarshalBinary(msg.Data)
if err != nil {
c.logf("ip rule deleted; failed to parse netlink message: %v", err)
} else {
c.logf("ip rule deleted: %+v", rmsg)
// On `ip -4 rule del pref 5210 table main`, logs:
// monitor: ip rule deleted: {Family:2 DstLength:0 SrcLength:0 Tos:0 Table:254 Protocol:0 Scope:0 Type:1 Flags:0 Attributes:{Dst:<nil> Src:<nil> Gateway:<nil> OutIface:0 Priority:5210 Table:254 Mark:4294967295 Expires:<nil> Metrics:<nil> Multipath:[]}}
}
return ipRuleDeletedMessage{}, nil
default:
c.logf("unhandled netlink msg type %+v, %q", msg.Header, msg.Data)
return unspecifiedMessage{}, nil
@ -174,3 +189,7 @@ func (m *newAddrMessage) ignore() bool {
type ignoreMessage struct{}
func (ignoreMessage) ignore() bool { return true }
type ipRuleDeletedMessage struct{}
func (ipRuleDeletedMessage) ignore() bool { return false }