agent: send SIGKILL instead of SIGTERM to container init process

If container initProcess doesn't install any handler for SIGTERM,
it will ignore this signal, thus send it SIGKILL instead of SIGTERM
to terminate it.

Fixes:#525

Signed-off-by: lifupan <lifupan@gmail.com>

grpc.go

@@ -7,6 +7,7 @@
 package main
 
 import (
+	"bufio"
 	"bytes"
 	"encoding/json"
 	"fmt"
@@ -833,6 +834,16 @@ func (a *agentGRPC) SignalProcess(ctx context.Context, req *pb.SignalProcessRequ
 	if req.ExecId == "" || status == libcontainer.Paused {
 		return emptyResp, ctr.container.Signal(signal, true)
 	} else if ctr.initProcess.id == req.ExecId {
+		pid, err := ctr.initProcess.process.Pid()
+		if err != nil {
+			return emptyResp, err
+		}
+		// For container initProcess, if it hasn't installed handler for "SIGTERM" signal,
+		// it will ignore the "SIGTERM" signal sent to it, thus send it "SIGKILL" signal
+		// instead of "SIGTERM" to terminate it.
+		if signal == syscall.SIGTERM && !isSignalHandled(pid, syscall.SIGTERM) {
+			signal = syscall.SIGKILL
+		}
 		return emptyResp, ctr.container.Signal(signal, false)
 	}
 
@@ -848,6 +859,39 @@ func (a *agentGRPC) SignalProcess(ctx context.Context, req *pb.SignalProcessRequ
 	return emptyResp, nil
 }
 
+// Check is the container process installed the
+// handler for specific signal.
+func isSignalHandled(pid int, signum syscall.Signal) bool {
+	var sigMask uint64 = 1 << (uint(signum) - 1)
+	procFile := fmt.Sprintf("/proc/%d/status", pid)
+	file, err := os.Open(procFile)
+	if err != nil {
+		agentLog.WithField("procFile", procFile).Warn("Open proc file failed")
+		return false
+	}
+	defer file.Close()
+
+	scanner := bufio.NewScanner(file)
+	for scanner.Scan() {
+		line := scanner.Text()
+		if strings.HasPrefix(line, "SigCgt:") {
+			maskSlice := strings.Split(line, ":")
+			if len(maskSlice) != 2 {
+				agentLog.WithField("procFile", procFile).Warn("Parse the SigCgt field failed")
+				return false
+			}
+			sigCgtStr := strings.TrimSpace(maskSlice[1])
+			sigCgtMask, err := strconv.ParseUint(sigCgtStr, 16, 64)
+			if err != nil {
+				agentLog.WithField("sigCgt", sigCgtStr).Warn("parse the SigCgt to hex failed")
+				return false
+			}
+			return (sigCgtMask & sigMask) == sigMask
+		}
+	}
+	return false
+}
+
 func (a *agentGRPC) WaitProcess(ctx context.Context, req *pb.WaitProcessRequest) (*pb.WaitProcessResponse, error) {
 	proc, ctr, err := a.sandbox.getProcess(req.ContainerId, req.ExecId)
 	if err != nil {

grpc_test.go

@@ -15,6 +15,7 @@ import (
 	"reflect"
 	"sort"
 	"strconv"
+	"syscall"
 	"testing"
 	"time"
 
@@ -836,3 +837,23 @@ func TestCopyFile(t *testing.T) {
 	// check file's content
 	assert.Equal(content, append(part1, part2...))
 }
+
+func TestIsSignalHandled(t *testing.T) {
+	assert := assert.New(t)
+	pid := 1
+
+	// process will not handle SIGKILL signal
+	signum := syscall.SIGKILL
+	handled := isSignalHandled(pid, signum)
+	assert.False(handled)
+
+	// init process will not handle SIGTERM signal
+	signum = syscall.SIGTERM
+	handled = isSignalHandled(pid, signum)
+	assert.False(handled)
+
+	// init process will handle the SIGQUIT signal
+	signum = syscall.SIGQUIT
+	handled = isSignalHandled(pid, signum)
+	assert.True(handled)
+}