From 4ddd0d2ffc7073f2d55ffb6777e3a168af0051f0 Mon Sep 17 00:00:00 2001
From: James O'Doherty <james@theodohertyfamily.com>
Date: Fri, 29 May 2026 20:11:07 -0400
Subject: Refactor rootless namespace joining to use C launcher

Fix an architectural shortfall where concurrent sessions failed to share
the target network and mount namespaces. Because the Go runtime is
multi-threaded, calling unix.Setns with CLONE_NEWNS from Go always returned
EINVAL, silently forcing concurrent runs to fall back to bootstrapping separate
isolated namespaces and separate WireGuard connections.

This commit resolves the issue by extending the embedded single-threaded C
launcher to handle namespace joining, and introducing a host-to-isolated path
propagation pattern:

1. Launcher setns Support: The C launcher now checks for WG_WRAP_JOIN_PID in
   the environment. If present, it joins the User, Mount, and Network
   namespaces of the active PID in single-threaded mode before executing the Go
   binary.
2. BootstrapJoin Integration: Implemented namespace.BootstrapJoin to
   transition joining sessions via the launcher.
3. Path Preservation: Export WG_WRAP_HOST_RUNTIME_BASE_DIR from the host to ensure
   the isolated instance maps the profile and PID directories to the exact
   same location.
4. Redundant Tunnel Bypass: Detect joined sessions via WG_WRAP_JOINED=1 in the CLI
   and bypass starting a duplicate WireGuard tunnel on the occupied tun0.
5. Testing: Added tests/e2e/sharing_test.go to assert namespace ID equality,
   which now passes successfully.
6. Git Tracking: Fixed .gitignore overmatch to stop ignoring cmd/wg-wrap/.
---
 internal/namespace/pinning.go | 66 ++++++-------------------------------------
 1 file changed, 8 insertions(+), 58 deletions(-)

(limited to 'internal/namespace/pinning.go')

diff --git a/internal/namespace/pinning.go b/internal/namespace/pinning.go
index 2433203..a522f17 100644
--- a/internal/namespace/pinning.go
+++ b/internal/namespace/pinning.go
@@ -6,12 +6,9 @@ import (
 	"fmt"
 	"os"
 	"path/filepath"
-	"runtime"
 	"strconv"
-	"syscall"
 
 	"git.theodohertyfamily.com/tools/wg-wrap/internal/paths"
-	"golang.org/x/sys/unix"
 )
 
 // PinNamespace touches the namespace path to indicate it is pinned/active.
@@ -53,77 +50,30 @@ func UnpinNamespace(pm *paths.PathManager, profile string) error {
 	return nil
 }
 
-// JoinExistingNamespace attempts to join the namespaces (user, mount, net)
-// of an already active process running under the same profile.
-// Returns true if a namespace was successfully joined, false if no active namespace exists.
-func JoinExistingNamespace(pm *paths.PathManager, profile string) (bool, error) {
+// FindActiveProfilePid looks for an active PID running under the specified profile.
+// Returns 0 if no active process is found.
+func FindActiveProfilePid(pm *paths.PathManager, profile string) (int, error) {
 	if err := PruneStalePids(pm, profile); err != nil {
-		return false, fmt.Errorf("failed to prune stale pids: %w", err)
+		return 0, fmt.Errorf("failed to prune stale pids: %w", err)
 	}
 
 	pidsDir := GetPidsDirPath(pm, profile)
 	files, err := os.ReadDir(pidsDir)
 	if err != nil {
 		if os.IsNotExist(err) {
-			return false, nil
+			return 0, nil
 		}
-		return false, fmt.Errorf("failed to read pids dir: %w", err)
+		return 0, fmt.Errorf("failed to read pids dir: %w", err)
 	}
 
-	var activePid int
 	for _, file := range files {
 		pid, err := strconv.Atoi(file.Name())
 		if err != nil {
 			continue
 		}
 		// Since we already pruned stale pids, the first file we find is an active pid!
-		activePid = pid
-		break
+		return pid, nil
 	}
 
-	if activePid == 0 {
-		return false, nil
-	}
-
-	// Lock the OS thread before joining namespaces to ensure this goroutine stays on the modified thread,
-	// and that the thread is not reused for other goroutines (since we never unlock it).
-	runtime.LockOSThread()
-
-	// Join User Namespace first
-	userNsPath := fmt.Sprintf("/proc/%d/ns/user", activePid)
-	userFd, err := os.Open(userNsPath)
-	if err != nil {
-		return false, fmt.Errorf("failed to open user namespace: %w", err)
-	}
-	defer func() { _ = userFd.Close() }()
-
-	if err := unix.Setns(int(userFd.Fd()), syscall.CLONE_NEWUSER); err != nil {
-		return false, fmt.Errorf("failed to join user namespace: %w", err)
-	}
-
-	// Join Mount Namespace
-	mntNsPath := fmt.Sprintf("/proc/%d/ns/mnt", activePid)
-	mntFd, err := os.Open(mntNsPath)
-	if err != nil {
-		return false, fmt.Errorf("failed to open mount namespace: %w", err)
-	}
-	defer func() { _ = mntFd.Close() }()
-
-	if err := unix.Setns(int(mntFd.Fd()), syscall.CLONE_NEWNS); err != nil {
-		return false, fmt.Errorf("failed to join mount namespace: %w", err)
-	}
-
-	// Join Network Namespace
-	netNsPath := fmt.Sprintf("/proc/%d/ns/net", activePid)
-	netFd, err := os.Open(netNsPath)
-	if err != nil {
-		return false, fmt.Errorf("failed to open network namespace: %w", err)
-	}
-	defer func() { _ = netFd.Close() }()
-
-	if err := unix.Setns(int(netFd.Fd()), syscall.CLONE_NEWNET); err != nil {
-		return false, fmt.Errorf("failed to join network namespace: %w", err)
-	}
-
-	return true, nil
+	return 0, nil
 }
-- 
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