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5c1738fd56
Add a vmtest TestExitNode that brings up a client, two exit nodes, and a non-Tailscale webserver, each on its own NAT'd vnet network with a distinct WAN IP. The test cycles the client's exit node setting between off, exit1, and exit2 and asserts that the webserver echoes the expected post-NAT source IP for each. Three pieces were needed to make this work: vnet now forwards TCP between simulated networks at the packet level, mirroring the existing UDP path. When a guest VM sends TCP to another simulated network's WAN IP, the source network's gateway rewrites src via doNATOut and routeTCPPacket hands the packet off to the destination network, which rewrites dst via doNATIn and writes the rewritten frame onto the destination LAN. The TCP stacks of the two guest VM kernels talk end-to-end; vnet just NATs the IP/port headers in flight, so all TCP semantics (handshakes, options, sequence numbers, payload) are preserved without a gvisor TCP termination in the middle. Adds a focused TestInterNetworkTCP that exercises this path without any Tailscale machinery. cmd/tta binds its outbound dial to the default route's interface using SO_BINDTODEVICE. Without that, the moment tailscaled installs 0.0.0.0/0 → tailscale0 in response to setting an exit node, TTA's existing TCP connection to test-driver gets rerouted through the exit node. From the test driver's perspective the connection's packets then arrive with the exit node's WAN IP as the source rather than the client's, so they don't match the existing flow and the connection is dead — manifesting in the test as a hang on EditPrefs (which had actually completed in milliseconds on the daemon side, but whose response never made it back). Pinning the socket to the underlying NIC keeps TTA's agent connection on a real interface regardless of any policy routing tailscaled installs later. We bind rather than carry the Tailscale bypass fwmark because the fwmark approach is conditional on tailscaled having configured SO_MARK-based policy routing, while binding is unconditional. vmtest grows an Env.SetExitNode helper that sets ExitNodeIP via EditPrefs through the agent, used by the new test. Updates #13038 Change-Id: I9fc8f91848b7aa2297ef3eaf71fed9d96056a024 Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
40 lines
1.3 KiB
Go
40 lines
1.3 KiB
Go
// Copyright (c) Tailscale Inc & contributors
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// SPDX-License-Identifier: BSD-3-Clause
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package main
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import (
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"fmt"
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"syscall"
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"golang.org/x/sys/unix"
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"tailscale.com/net/netmon"
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)
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// bypassControlFunc is set as net.Dialer.Control so that sockets dialed by
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// TTA bypass tailscaled's policy routing. Without it, sockets opened before
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// tailscaled installs an exit-node route would have their packets rerouted
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// via the exit node when the route is later installed, breaking the
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// existing connection.
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//
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// We bind the socket to the default route's interface (typically the VM's
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// LAN-facing NIC) rather than relying on the bypass fwmark. The fwmark
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// approach is conditional on tailscaled having configured SO_MARK-based
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// policy routing; binding to the underlying interface is unconditional.
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func bypassControlFunc(network, address string, c syscall.RawConn) error {
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ifc, err := netmon.DefaultRouteInterface()
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if err != nil {
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return fmt.Errorf("netmon.DefaultRouteInterface: %w", err)
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}
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var sockErr error
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if err := c.Control(func(fd uintptr) {
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sockErr = unix.SetsockoptString(int(fd), unix.SOL_SOCKET, unix.SO_BINDTODEVICE, ifc)
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}); err != nil {
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return err
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}
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if sockErr != nil {
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return fmt.Errorf("setting SO_BINDTODEVICE on %q: %w", ifc, sockErr)
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}
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return nil
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}
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