pam/integration-tests/exec: Add tests checking child behavior on signals

When the child receives signals should ignore them and just return a
generic PAM system error, but still we need to check that they're
properly handled

Author: 3v1n0

pam/integration-tests/cmd/exec-client/modulewrapper.go

@@ -5,8 +5,12 @@ package main
 import (
 	"context"
 	"errors"
+	"os"
+	"syscall"
+	"time"
 
 	"github.com/msteinert/pam/v2"
+	"github.com/ubuntu/authd/log"
 	"github.com/ubuntu/authd/pam/internal/dbusmodule"
 )
 
@@ -28,3 +32,20 @@ func (m *moduleWrapper) SimulateClientPanic(text string) {
 func (m *moduleWrapper) SimulateClientError(errorMsg string) error {
 	return errors.New(errorMsg)
 }
+
+// SimulateClientSignal sends a signal to the child process.
+func (m *moduleWrapper) SimulateClientSignal(sig syscall.Signal, shouldExit bool) {
+	pid := os.Getpid()
+	log.Debugf(context.Background(), "Sending signal %v to self pid (%v)",
+		sig, pid)
+
+	if err := syscall.Kill(pid, sig); err != nil {
+		log.Errorf(context.Background(), "Sending signal %v failed: %v", sig, err)
+		return
+	}
+
+	if shouldExit {
+		// The program is expected to exit once the signal is sent, so let's wait
+		<-time.After(24 * time.Hour)
+	}
+}

pam/integration-tests/exec_test.go

@@ -8,6 +8,7 @@ import (
 	"path/filepath"
 	"reflect"
 	"strings"
+	"syscall"
 	"testing"
 
 	"github.com/godbus/dbus/v5"
@@ -231,6 +232,14 @@ func TestExecModule(t *testing.T) {
 			methodCalls: []cliMethodCall{{m: "SimulateClientError", args: []any{"Client error!"}}},
 			wantError:   pam.ErrSystem,
 		},
+		"Error_when_client_fails_because_a_client_SIGTERM_signal": {
+			methodCalls: []cliMethodCall{{m: "SimulateClientSignal", args: []any{syscall.SIGTERM, true}}},
+			wantError:   pam.ErrSystem,
+		},
+		"Error_when_client_fails_because_a_client_SIGKILL_signal": {
+			methodCalls: []cliMethodCall{{m: "SimulateClientSignal", args: []any{syscall.SIGKILL, true}}},
+			wantError:   pam.ErrSystem,
+		},
 	}
 	for name, tc := range cliTests {
 		t.Run("Client "+name, func(t *testing.T) {
@@ -1006,6 +1015,8 @@ func getVariant(value any) dbus.Variant {
 	switch v := value.(type) {
 	case pam.Error:
 		return getVariant(int(v))
+	case syscall.Signal:
+		return getVariant(int(v))
 	case nil:
 		return getVariant("<@mv nothing>")
 	default: