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control/controlclient: report broken IP forwarding more precisely.

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IP forwarding is not required when advertising a machine's local IPs
over Tailscale.

Fixes #1435.

Signed-off-by: David Anderson <danderson@tailscale.com>
This commit is contained in:
David Anderson 2021-03-03 19:19:41 -08:00 committed by Dave Anderson
parent 0430c2dd12
commit 0b66cfe1e0
1 changed files with 16 additions and 2 deletions
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18
control/controlclient/direct.go
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@ -37,6 +37,7 @@ import (
"tailscale.com/log/logheap"
"tailscale.com/net/dnscache"
"tailscale.com/net/dnsfallback"
"tailscale.com/net/interfaces"
"tailscale.com/net/netns"
"tailscale.com/net/tlsdial"
"tailscale.com/net/tshttpproxy"
@ -546,7 +547,7 @@ func (c *Direct) sendMapRequest(ctx context.Context, maxPolls int, cb func(*netm
OmitPeers: cb == nil,
}
var extraDebugFlags []string
if hostinfo != nil && ipForwardingBroken(hostinfo.RoutableIPs) {
if hostinfo != nil && ipForwardingBroken(hostinfo.RoutableIPs, c.linkMon.InterfaceState()) {
extraDebugFlags = append(extraDebugFlags, "warn-ip-forwarding-off")
}
if health.RouterHealth() != nil {
@ -1141,7 +1142,7 @@ func TrimWGConfig() opt.Bool {
// and will definitely not work for the routes provided.
//
// It should not return false positives.
func ipForwardingBroken(routes []netaddr.IPPrefix) bool {
func ipForwardingBroken(routes []netaddr.IPPrefix, state *interfaces.State) bool {
if len(routes) == 0 {
// Nothing to route, so no need to warn.
return false
@ -1155,8 +1156,21 @@ func ipForwardingBroken(routes []netaddr.IPPrefix) bool {
return false
}
localIPs := map[netaddr.IP]bool{}
for _, addrs := range state.InterfaceIPs {
for _, pfx := range addrs {
localIPs[pfx.IP] = true
}
}
v4Routes, v6Routes := false, false
for _, r := range routes {
// It's possible to advertise a route to one of the local
// machine's local IPs. IP forwarding isn't required for this
// to work, so we shouldn't warn for such exports.
if r.IsSingleIP() && localIPs[r.IP] {
continue
}
if r.IP.Is4() {
v4Routes = true
} else {