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/launcher_src/launcher.c | 63 ++++++++++++++++++++++++++++++
 1 file changed, 63 insertions(+)

(limited to 'internal/namespace/launcher_src/launcher.c')

diff --git a/internal/namespace/launcher_src/launcher.c b/internal/namespace/launcher_src/launcher.c
index 7bbbce7..60c6558 100644
--- a/internal/namespace/launcher_src/launcher.c
+++ b/internal/namespace/launcher_src/launcher.c
@@ -13,6 +13,69 @@ int main(int argc, char **argv) {
         return 1;
     }
 
+    // Check if we are joining an existing namespace
+    char *join_pid_str = getenv("WG_WRAP_JOIN_PID");
+    if (join_pid_str != NULL && strlen(join_pid_str) > 0) {
+        int target_pid = atoi(join_pid_str);
+        if (target_pid > 0) {
+            char path[128];
+            int fd;
+
+            // 1. Join User Namespace first
+            snprintf(path, sizeof(path), "/proc/%d/ns/user", target_pid);
+            fd = open(path, O_RDONLY);
+            if (fd == -1) {
+                perror("open target user namespace");
+                return 1;
+            }
+            if (setns(fd, CLONE_NEWUSER) == -1) {
+                perror("setns CLONE_NEWUSER");
+                close(fd);
+                return 1;
+            }
+            close(fd);
+
+            // 2. Join Mount Namespace
+            snprintf(path, sizeof(path), "/proc/%d/ns/mnt", target_pid);
+            fd = open(path, O_RDONLY);
+            if (fd == -1) {
+                perror("open target mount namespace");
+                return 1;
+            }
+            if (setns(fd, CLONE_NEWNS) == -1) {
+                perror("setns CLONE_NEWNS");
+                close(fd);
+                return 1;
+            }
+            close(fd);
+
+            // 3. Join Network Namespace
+            snprintf(path, sizeof(path), "/proc/%d/ns/net", target_pid);
+            fd = open(path, O_RDONLY);
+            if (fd == -1) {
+                perror("open target network namespace");
+                return 1;
+            }
+            if (setns(fd, CLONE_NEWNET) == -1) {
+                perror("setns CLONE_NEWNET");
+                close(fd);
+                return 1;
+            }
+            close(fd);
+
+            // Execute the target command
+            if (argv[0] == NULL) {
+                fprintf(stderr, "No target binary provided in argv[0]\n");
+                return 1;
+            }
+            if (execv(argv[0], argv) == -1) {
+                perror("execv failed");
+                return 1;
+            }
+            return 0;
+        }
+    }
+
     // 1. Capture host identities BEFORE unsharing
     uid_t current_uid = getuid();
     gid_t current_gid = getgid();
-- 
cgit v1.2.3