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Fixes to route mirroring #40099

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9d6c794
route fixes from protonvpn testing
Mar 18, 2026
35dc5a2
add unit test, fix log
Mar 27, 2026
f5dab4d
ai code review
Apr 3, 2026
9c60a6d
format with vs 2022
Apr 6, 2026
832f9a4
review
Apr 7, 2026
f8b18f3
remove optional has_value checks
Apr 8, 2026
1cd758b
harden contracts for to, via having or not having values
Apr 9, 2026
6a5ac00
update IsOnlink check
Apr 9, 2026
4b8fa18
fix constructor parameters
Apr 9, 2026
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9 changes: 7 additions & 2 deletions src/linux/netlinkutil/Route.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -4,8 +4,13 @@
#include "Utils.h"

Route::Route(int family, const std::optional<Address>& via, int dev, bool defaultRoute, const std::optional<Address>& to, int metric) :
family(family), via(via), dev(dev), defaultRoute(defaultRoute), to(to), metric(metric)
family(family), via(nextHop), dev(dev), defaultRoute(defaultRoute), to(to), metric(metric)
{
// For onlink routes, ensure the via field is empty
if (via.has_value() && ((family == AF_INET && via->Addr() == "0.0.0.0") || (family == AF_INET6 && via->Addr() == "::")))
{
via.reset();
}
}

std::ostream& operator<<(std::ostream& out, const Route& route)
Expand All @@ -30,7 +35,7 @@ std::ostream& operator<<(std::ostream& out, const Route& route)

bool Route::IsOnlink() const
{
return !via.has_value() || (family == AF_INET && via->Addr() == "0.0.0.0") || (family == AF_INET6 && via->Addr() == "::");
return !via.has_value();
}

bool Route::IsMulticast() const
Expand Down
2 changes: 1 addition & 1 deletion src/linux/netlinkutil/Route.h
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Original file line number Diff line number Diff line change
Expand Up @@ -14,7 +14,7 @@ struct Route
int metric = 0;
bool isLoopbackRoute = false;

Route(int family, const std::optional<Address>& via, int dev, bool defaultRoute, const std::optional<Address>& to, int metric);
Route(int family, const std::optional<Address>& nextHop, int dev, bool defaultRoute, const std::optional<Address>& to, int metric);

bool IsOnlink() const;
bool IsMulticast() const;
Expand Down
85 changes: 67 additions & 18 deletions src/linux/netlinkutil/RoutingTable.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -111,6 +111,10 @@ void RoutingTable::ModifyRouteImpl(const Route& route, Operation action)
{
ModifyLoopbackRouteImpl<TAddr>(route, operation, flags);
}
else if (route.defaultRoute && route.IsOnlink())
{
ModifyDefaultLinkLocalRouteImpl<TAddr>(route, operation, flags);
}
else if (route.defaultRoute)
{
ModifyDefaultRouteImpl<TAddr>(route, operation, flags);
Expand Down Expand Up @@ -181,7 +185,7 @@ void RoutingTable::ModifyLoopbackRouteImpl(const Route& route, int operation, in
{
if (!route.to.has_value() || !route.via.has_value())
{
throw RuntimeErrorWithSourceLocation(std::format("Loopback route {} missing destination or gateway address", utils::Stringify(route)));
throw RuntimeErrorWithSourceLocation(std::format("Loopback route {} missing destination or next hop", utils::Stringify(route)));
}

struct Message : RouteMessage
Expand All @@ -193,8 +197,8 @@ void RoutingTable::ModifyLoopbackRouteImpl(const Route& route, int operation, in

GNS_LOG_INFO(
"SendMessage Route (to {}, via {}), operation ({}), netLinkflags ({})",
route.to.has_value() ? route.to.value().Addr().c_str() : "[empty]",
route.via.has_value() ? route.via.value().Addr().c_str() : "[empty]",
route.to.value().Addr().c_str(),
route.via.value().Addr().c_str(),
RouteOperationToString(operation),
NetLinkFormatFlagsToString(flags).c_str());

Expand Down Expand Up @@ -222,20 +226,52 @@ void RoutingTable::ModifyLoopbackRouteImpl(const Route& route, int operation, in

message.route.rtm_flags |= RTNH_F_ONLINK;
GNS_LOG_INFO(
"InitializeAddressAttribute RTA_DST ({}) RTA_GATEWAY ({}) RTA_PRIORITY ([not set])",
"Netlink message configuration: RTA_DST ({}) RTA_GATEWAY ({}) RTA_PRIORITY ([not set])",
route.to.value().Addr().c_str(),
route.via.value().Addr().c_str());
utils::InitializeAddressAttribute<TAddr>(message.to, route.to.value(), RTA_DST);
utils::InitializeAddressAttribute<TAddr>(message.via, route.via.value(), RTA_GATEWAY);
});
}

template <typename TAddr>
void RoutingTable::ModifyDefaultLinkLocalRouteImpl(const Route& route, int operation, int flags)
{
if (route.via.has_value())
{
throw RuntimeErrorWithSourceLocation("Default route has unexpected next hop");
}
if (route.to.has_value())
{
throw RuntimeErrorWithSourceLocation("Default route has unexpected destination address");
}

struct Message : RouteMessage
{
utils::IntegerAttribute metric;
} __attribute__((packed));

GNS_LOG_INFO(
"SendMessage Route (default onlink), operation ({}), netLinkflags ({})",
RouteOperationToString(operation),
NetLinkFormatFlagsToString(flags).c_str());

SendMessage<Message>(route, operation, flags, [&](Message& message) {
GNS_LOG_INFO("Netlink message configuration: RTA_DST ([not set]) RTA_GATEWAY ([not set]), RTA_PRIORITY ({})", route.metric);
utils::InitializeIntegerAttribute(message.metric, route.metric, RTA_PRIORITY);
});
}

template <typename TAddr>
void RoutingTable::ModifyDefaultRouteImpl(const Route& route, int operation, int flags)
{
if (!route.via.has_value())
{
throw RuntimeErrorWithSourceLocation("Default route is missing its gateway address");
throw RuntimeErrorWithSourceLocation("Default route is missing its next hop");
}
if (route.to.has_value())
{
throw RuntimeErrorWithSourceLocation("Default route has unexpected destination address");
}

struct Message : RouteMessage
Expand All @@ -246,15 +282,15 @@ void RoutingTable::ModifyDefaultRouteImpl(const Route& route, int operation, int

GNS_LOG_INFO(
"SendMessage Route (to {}, via {}), operation ({}), netLinkflags ({})",
route.to.has_value() ? route.to.value().Addr().c_str() : "[empty]",
route.via.has_value() ? route.via.value().Addr().c_str() : "[empty]",
"[empty]",
route.via.value().Addr().c_str(),
RouteOperationToString(operation),
NetLinkFormatFlagsToString(flags).c_str());

SendMessage<Message>(route, operation, flags, [&](Message& message) {
GNS_LOG_INFO(
"InitializeAddressAttribute RTA_DST ([not set]) RTA_GATEWAY ({}), RTA_PRIORITY ({})",
route.to.has_value() ? route.to.value().Addr().c_str() : "[empty]",
"Netlink message configuration: RTA_DST ([not set]) RTA_GATEWAY ({}), RTA_PRIORITY ({})",
route.via.value().Addr().c_str(),
route.metric);
utils::InitializeAddressAttribute<TAddr>(message.via, route.via.value(), RTA_GATEWAY);
utils::InitializeIntegerAttribute(message.metric, route.metric, RTA_PRIORITY);
Expand All @@ -264,6 +300,15 @@ void RoutingTable::ModifyDefaultRouteImpl(const Route& route, int operation, int
template <typename TAddr>
void RoutingTable::ModifyLinkLocalRouteImpl(const Route& route, int operation, int flags)
{
if (!route.to.has_value())
{
throw RuntimeErrorWithSourceLocation("Link-local route is missing its destination address");
}
if (route.via.has_value())
{
throw RuntimeErrorWithSourceLocation("Link-local route has unexpected next hop");
}

struct Message : RouteMessage
{
utils::AddressAttribute<TAddr> to;
Expand All @@ -272,15 +317,15 @@ void RoutingTable::ModifyLinkLocalRouteImpl(const Route& route, int operation, i

GNS_LOG_INFO(
"SendMessage Route (to {}, via {}), operation ({}), netLinkflags ({})",
route.to.has_value() ? route.to.value().Addr().c_str() : "[empty]",
route.via.has_value() ? route.via.value().Addr().c_str() : "[empty]",
route.to.value().Addr().c_str(),
"[empty]",
RouteOperationToString(operation),
NetLinkFormatFlagsToString(flags).c_str());

SendMessage<Message>(route, operation, flags, [&](Message& message) {
GNS_LOG_INFO(
"InitializeAddressAttribute RTA_DST ({}) RTA_GATEWAY ([not set]), RTA_PRIORITY ({})",
route.to.has_value() ? route.to.value().Addr().c_str() : "[empty]",
"Netlink message configuration: RTA_DST ({}) RTA_GATEWAY ([not set]), RTA_PRIORITY ({})",
route.to.value().Addr().c_str(),
route.metric);
utils::InitializeAddressAttribute<TAddr>(message.to, route.to.value(), RTA_DST);
utils::InitializeIntegerAttribute(message.metric, route.metric, RTA_PRIORITY);
Expand All @@ -294,6 +339,10 @@ void RoutingTable::ModifyOfflinkRouteImpl(const Route& route, int operation, int
{
throw RuntimeErrorWithSourceLocation("Offlink route is missing its next hop");
}
if (!route.to.has_value())
{
throw RuntimeErrorWithSourceLocation("Offlink route is missing its destination address");
}

struct Message : RouteMessage
{
Expand All @@ -304,16 +353,16 @@ void RoutingTable::ModifyOfflinkRouteImpl(const Route& route, int operation, int

GNS_LOG_INFO(
"SendMessage Route (to {}, via {}), operation ({}), netLinkflags ({})",
route.to.has_value() ? route.to.value().Addr().c_str() : "[empty]",
route.via.has_value() ? route.via.value().Addr().c_str() : "[empty]",
route.to.value().Addr().c_str(),
route.via.value().Addr().c_str(),
RouteOperationToString(operation),
NetLinkFormatFlagsToString(flags).c_str());

SendMessage<Message>(route, operation, flags, [&](Message& message) {
GNS_LOG_INFO(
"InitializeAddressAttribute RTA_DST ({}) RTA_GATEWAY ({}), RTA_PRIORITY ({})",
route.to.has_value() ? route.to.value().Addr().c_str() : "[empty]",
route.via.has_value() ? route.via.value().Addr().c_str() : "[empty]",
"Netlink message configuration: RTA_DST ({}) RTA_GATEWAY ({}), RTA_PRIORITY ({})",
route.to.value().Addr().c_str(),
route.via.value().Addr().c_str(),
route.metric);
utils::InitializeAddressAttribute<TAddr>(message.to, route.to.value(), RTA_DST);
utils::InitializeAddressAttribute<TAddr>(message.via, route.via.value(), RTA_GATEWAY);
Expand Down
3 changes: 3 additions & 0 deletions src/linux/netlinkutil/RoutingTable.h
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Original file line number Diff line number Diff line change
Expand Up @@ -51,6 +51,9 @@ class RoutingTable
template <typename TAddr>
void ModifyDefaultRouteImpl(const Route& route, int operation, int flags);

template <typename TAddr>
void ModifyDefaultLinkLocalRouteImpl(const Route& route, int operation, int flags);

template <typename TAddr>
void ModifyLinkLocalRouteImpl(const Route& route, int operation, int flags);

Expand Down
9 changes: 9 additions & 0 deletions src/windows/service/exe/WslMirroredNetworking.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -347,6 +347,15 @@ void wsl::core::networking::WslMirroredNetworkManager::ProcessRouteChange()
{
endpointRoute.Metric = UINT16_MAX;
}

// Some Windows interfaces (like VPNs) can have metric 0 and routes over that interface with metric also 0, adding
// up to 0. Linux treats metric 0 as unspecified and will default to a 1024 metric. The highest priority metric in
// Linux is 1 instead so we need to switch the metric from 0 to 1.
if (endpointRoute.Metric == 0)
{
endpointRoute.Metric = 1;
}

endpoint.Network->Routes.insert(endpointRoute);
}
}
Expand Down
37 changes: 37 additions & 0 deletions test/windows/NetworkTests.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -352,6 +352,43 @@ class NetworkTests
VERIFY_ARE_EQUAL(v6State.DefaultRoute->Device, L"eth0");
}

TEST_METHOD(AddRemoveDefaultOnlinkRoutes)
{
WSL2_TEST_ONLY();

wsl::shared::hns::Route defaultRouteV4;
defaultRouteV4.NextHop = L"0.0.0.0";
defaultRouteV4.DestinationPrefix = LX_INIT_DEFAULT_ROUTE_PREFIX;
defaultRouteV4.Family = AF_INET;
defaultRouteV4.Metric = 1;
SendDeviceSettingsRequest(L"eth0", defaultRouteV4, ModifyRequestType::Add, GuestEndpointResourceType::Route);

wsl::shared::hns::Route defaultRouteV6;
defaultRouteV6.NextHop = L"::";
defaultRouteV6.DestinationPrefix = LX_INIT_DEFAULT_ROUTE_V6_PREFIX;
defaultRouteV6.Family = AF_INET6;
defaultRouteV6.Metric = 1;
SendDeviceSettingsRequest(L"eth0", defaultRouteV6, ModifyRequestType::Add, GuestEndpointResourceType::Route);

const bool defaultV4RouteExists =
LxsstuLaunchWsl(L"ip -4 route show | grep \"default dev eth0\" | grep -w \"metric 1\"") == (DWORD)0;
const bool defaultV6RouteExists =
LxsstuLaunchWsl(L"ip -6 route show | grep \"default dev eth0\" | grep -w \"metric 1\"") == (DWORD)0;

SendDeviceSettingsRequest(L"eth0", defaultRouteV4, ModifyRequestType::Remove, GuestEndpointResourceType::Route);
SendDeviceSettingsRequest(L"eth0", defaultRouteV6, ModifyRequestType::Remove, GuestEndpointResourceType::Route);

const bool defaultV4RouteRemoved =
LxsstuLaunchWsl(L"ip -4 route show | grep \"default dev eth0\" | grep -w \"metric 1\"") != (DWORD)0;
const bool defaultV6RouteRemoved =
LxsstuLaunchWsl(L"ip -6 route show | grep \"default dev eth0\" | grep -w \"metric 1\"") != (DWORD)0;

VERIFY_IS_TRUE(defaultV4RouteExists);
VERIFY_IS_TRUE(defaultV6RouteExists);
VERIFY_IS_TRUE(defaultV4RouteRemoved);
VERIFY_IS_TRUE(defaultV6RouteRemoved);
}

TEST_METHOD(SetInterfaceDownAndUp)
{
WSL2_TEST_ONLY();
Expand Down
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