fix: race-detection between parent and child processes (#106)

Author: evgeniy-scherbina

app/child.go

@@ -1,19 +1,66 @@
 package app
 
 import (
+	"context"
 	"fmt"
 	"log"
 	"log/slog"
 	"os"
 	"os/exec"
+	"syscall"
+	"time"
 
+	"github.com/cenkalti/backoff/v5"
 	"github.com/coder/boundary/jail"
+	"golang.org/x/sys/unix"
 )
 
+// waitForInterface waits for a network interface to appear in the namespace.
+// It retries checking for the interface with exponential backoff up to the specified timeout.
+func waitForInterface(interfaceName string, timeout time.Duration) error {
+	b := backoff.NewExponentialBackOff()
+	b.InitialInterval = 50 * time.Millisecond
+	b.MaxInterval = 500 * time.Millisecond
+	b.Multiplier = 2.0
+
+	ctx, cancel := context.WithTimeout(context.Background(), timeout)
+	defer cancel()
+
+	operation := func() (bool, error) {
+		cmd := exec.Command("ip", "link", "show", interfaceName)
+		cmd.SysProcAttr = &syscall.SysProcAttr{
+			AmbientCaps: []uintptr{uintptr(unix.CAP_NET_ADMIN)},
+		}
+
+		err := cmd.Run()
+		if err != nil {
+			return false, fmt.Errorf("interface %s not found: %w", interfaceName, err)
+		}
+		// Interface exists
+		return true, nil
+	}
+
+	_, err := backoff.Retry(ctx, operation, backoff.WithBackOff(b))
+	if err != nil {
+		return fmt.Errorf("interface %s did not appear within %v: %w", interfaceName, timeout, err)
+	}
+
+	return nil
+}
+
 func RunChild(logger *slog.Logger, args []string) error {
 	logger.Info("boundary CHILD process is started")
 
 	vethNetJail := os.Getenv("VETH_JAIL_NAME")
+	if vethNetJail == "" {
+		return fmt.Errorf("VETH_JAIL_NAME environment variable is not set")
+	}
+
+	// Wait for the veth interface to be moved into the namespace by the parent process
+	if err := waitForInterface(vethNetJail, 5*time.Second); err != nil {
+		return fmt.Errorf("failed to wait for interface %s: %w", vethNetJail, err)
+	}
+
 	err := jail.SetupChildNetworking(vethNetJail)
 	if err != nil {
 		return fmt.Errorf("failed to setup child networking: %v", err)

go.mod

@@ -3,6 +3,7 @@ module github.com/coder/boundary
 go 1.24.0
 
 require (
+	github.com/cenkalti/backoff/v5 v5.0.3
 	github.com/coder/serpent v0.10.0
 	github.com/stretchr/testify v1.8.4
 	golang.org/x/sys v0.38.0

go.sum

@@ -10,6 +10,8 @@ cloud.google.com/go/longrunning v0.5.1 h1:Fr7TXftcqTudoyRJa113hyaqlGdiBQkp0Gq7tE
 cloud.google.com/go/longrunning v0.5.1/go.mod h1:spvimkwdz6SPWKEt/XBij79E9fiTkHSQl/fRUUQJYJc=
 github.com/aymanbagabas/go-osc52/v2 v2.0.1 h1:HwpRHbFMcZLEVr42D4p7XBqjyuxQH5SMiErDT4WkJ2k=
 github.com/aymanbagabas/go-osc52/v2 v2.0.1/go.mod h1:uYgXzlJ7ZpABp8OJ+exZzJJhRNQ2ASbcXHWsFqH8hp8=
+github.com/cenkalti/backoff/v5 v5.0.3 h1:ZN+IMa753KfX5hd8vVaMixjnqRZ3y8CuJKRKj1xcsSM=
+github.com/cenkalti/backoff/v5 v5.0.3/go.mod h1:rkhZdG3JZukswDf7f0cwqPNk4K0sa+F97BxZthm/crw=
 github.com/charmbracelet/lipgloss v0.8.0 h1:IS00fk4XAHcf8uZKc3eHeMUTCxUH6NkaTrdyCQk84RU=
 github.com/charmbracelet/lipgloss v0.8.0/go.mod h1:p4eYUZZJ/0oXTuCQKFF8mqyKCz0ja6y+7DniDDw5KKU=
 github.com/coder/pretty v0.0.0-20230908205945-e89ba86370e0 h1:3A0ES21Ke+FxEM8CXx9n47SZOKOpgSE1bbJzlE4qPVs=