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mesh: set src for encapsulated tunl routes #5

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mesh: set src for encapsulated tunl routes #5

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7 changes: 6 additions & 1 deletion pkg/mesh/routes.go
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Original file line number Diff line number Diff line change
Expand Up @@ -76,6 +76,7 @@ func (t *Topology) Routes(kiloIfaceName string, kiloIface, privIface, tunlIface
Flags: int(netlink.FLAG_ONLINK),
Gw: segment.privateIPs[i],
LinkIndex: tunlIface,
Src: t.privateIP.IP,
Protocol: unix.RTPROT_STATIC,
Table: kiloTableIndex,
})
Expand Down Expand Up @@ -161,6 +162,7 @@ func (t *Topology) Routes(kiloIfaceName string, kiloIface, privIface, tunlIface
Flags: int(netlink.FLAG_ONLINK),
Gw: segment.privateIPs[i],
LinkIndex: tunlIface,
Src: t.privateIP.IP,
Protocol: unix.RTPROT_STATIC,
Table: kiloTableIndex,
})
Expand Down Expand Up @@ -304,8 +306,11 @@ func (t *Topology) PeerRoutes(name string, kiloIface int, additionalAllowedIPs [
}

func encapsulateRoute(route *netlink.Route, encapsulate encapsulation.Strategy, subnet *net.IPNet, tunlIface int) *netlink.Route {
if encapsulate == encapsulation.Always || (encapsulate == encapsulation.CrossSubnet && !subnet.Contains(route.Gw)) {
if encapsulate == encapsulation.Always || (encapsulate == encapsulation.CrossSubnet && subnet != nil && !subnet.Contains(route.Gw)) {
route.LinkIndex = tunlIface
if subnet != nil && route.Src == nil {
route.Src = subnet.IP
}
}
Comment on lines +309 to 314
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@gemini-code-assist gemini-code-assist bot Feb 13, 2026

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high

The current logic for encapsulation when encapsulate == encapsulation.Always and subnet == nil could lead to issues. In this scenario, the route's LinkIndex is updated to tunlIface to enable encapsulation, but the source IP (Src) is not set. This might cause the kernel to select an incorrect source IP for the encapsulated packets.

To prevent this, we should avoid encapsulation altogether if a source IP (subnet) is not available.

I suggest modifying the condition to ensure subnet is not nil before attempting any encapsulation logic. This makes the function more robust and avoids creating potentially misconfigured routes.

Suggested change
if encapsulate == encapsulation.Always || (encapsulate == encapsulation.CrossSubnet && subnet != nil && !subnet.Contains(route.Gw)) {
route.LinkIndex = tunlIface
if subnet != nil && route.Src == nil {
route.Src = subnet.IP
}
}
if subnet != nil && (encapsulate == encapsulation.Always || (encapsulate == encapsulation.CrossSubnet && !subnet.Contains(route.Gw))) {
route.LinkIndex = tunlIface
if route.Src == nil {
route.Src = subnet.IP
}
}

return route
}
Expand Down
13 changes: 13 additions & 0 deletions pkg/mesh/routes_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -680,13 +680,15 @@ func TestRoutes(t *testing.T) {
Flags: int(netlink.FLAG_ONLINK),
Gw: nodes["c"].InternalIP.IP,
LinkIndex: tunlIface,
Src: nodes["b"].InternalIP.IP,
Protocol: unix.RTPROT_STATIC,
},
{
Dst: oneAddressCIDR(nodes["c"].InternalIP.IP),
Flags: int(netlink.FLAG_ONLINK),
Gw: nodes["c"].InternalIP.IP,
LinkIndex: tunlIface,
Src: nodes["b"].InternalIP.IP,
Protocol: unix.RTPROT_STATIC,
Table: kiloTableIndex,
},
Expand Down Expand Up @@ -815,41 +817,47 @@ func TestRoutes(t *testing.T) {
Flags: int(netlink.FLAG_ONLINK),
Gw: nodes["b"].InternalIP.IP,
LinkIndex: tunlIface,
Src: nodes["c"].InternalIP.IP,
Protocol: unix.RTPROT_STATIC,
},
{
Dst: nodes["a"].Subnet,
Flags: int(netlink.FLAG_ONLINK),
Gw: nodes["b"].InternalIP.IP,
LinkIndex: tunlIface,
Src: nodes["c"].InternalIP.IP,
Protocol: unix.RTPROT_STATIC,
},
{
Dst: oneAddressCIDR(nodes["a"].InternalIP.IP),
Flags: int(netlink.FLAG_ONLINK),
Gw: nodes["b"].InternalIP.IP,
LinkIndex: tunlIface,
Src: nodes["c"].InternalIP.IP,
Protocol: unix.RTPROT_STATIC,
},
{
Dst: oneAddressCIDR(mustTopoForGranularityAndHost(LogicalGranularity, nodes["c"].Name).segments[1].wireGuardIP),
Flags: int(netlink.FLAG_ONLINK),
Gw: nodes["b"].InternalIP.IP,
LinkIndex: tunlIface,
Src: nodes["c"].InternalIP.IP,
Protocol: unix.RTPROT_STATIC,
},
{
Dst: nodes["b"].Subnet,
Flags: int(netlink.FLAG_ONLINK),
Gw: nodes["b"].InternalIP.IP,
LinkIndex: tunlIface,
Src: nodes["c"].InternalIP.IP,
Protocol: unix.RTPROT_STATIC,
},
{
Dst: nodes["b"].InternalIP,
Flags: int(netlink.FLAG_ONLINK),
Gw: nodes["b"].InternalIP.IP,
LinkIndex: tunlIface,
Src: nodes["c"].InternalIP.IP,
Protocol: unix.RTPROT_STATIC,
Table: kiloTableIndex,
},
Expand All @@ -858,34 +866,39 @@ func TestRoutes(t *testing.T) {
Flags: int(netlink.FLAG_ONLINK),
Gw: nodes["b"].InternalIP.IP,
LinkIndex: tunlIface,
Src: nodes["c"].InternalIP.IP,
Protocol: unix.RTPROT_STATIC,
},
{
Dst: nodes["d"].Subnet,
Flags: int(netlink.FLAG_ONLINK),
Gw: nodes["b"].InternalIP.IP,
LinkIndex: tunlIface,
Src: nodes["c"].InternalIP.IP,
Protocol: unix.RTPROT_STATIC,
},
{
Dst: &peers["a"].AllowedIPs[0],
Flags: int(netlink.FLAG_ONLINK),
Gw: nodes["b"].InternalIP.IP,
LinkIndex: tunlIface,
Src: nodes["c"].InternalIP.IP,
Protocol: unix.RTPROT_STATIC,
},
{
Dst: &peers["a"].AllowedIPs[1],
Flags: int(netlink.FLAG_ONLINK),
Gw: nodes["b"].InternalIP.IP,
LinkIndex: tunlIface,
Src: nodes["c"].InternalIP.IP,
Protocol: unix.RTPROT_STATIC,
},
{
Dst: &peers["b"].AllowedIPs[0],
Flags: int(netlink.FLAG_ONLINK),
Gw: nodes["b"].InternalIP.IP,
LinkIndex: tunlIface,
Src: nodes["c"].InternalIP.IP,
Protocol: unix.RTPROT_STATIC,
},
},
Expand Down