Synchronize signalling with S/R

This is to fix a data race between sending an external signal to
a ThreadGroup and kernel saving state for S/R.

PiperOrigin-RevId: 295244281

2 files changed, 12 insertions, 4 deletions

diff --git a/pkg/sentry/kernel/kernel.go b/pkg/sentry/kernel/kernel.go
index ea21af33f..7da0368f1 100644
--- a/pkg/sentry/kernel/kernel.go
+++ b/pkg/sentry/kernel/kernel.go
@@ -1169,6 +1169,14 @@ func (k *Kernel) SendExternalSignal(info *arch.SignalInfo, context string) {
 	k.sendExternalSignal(info, context)
 }
 
+// SendExternalSignalThreadGroup injects a signal into an specific ThreadGroup.
+// This function doesn't skip signals like SendExternalSignal does.
+func (k *Kernel) SendExternalSignalThreadGroup(tg *ThreadGroup, info *arch.SignalInfo) error {
+	k.extMu.Lock()
+	defer k.extMu.Unlock()
+	return tg.SendSignal(info)
+}
+
 // SendContainerSignal sends the given signal to all processes inside the
 // namespace that match the given container ID.
 func (k *Kernel) SendContainerSignal(cid string, info *arch.SignalInfo) error {
diff --git a/runsc/boot/loader.go b/runsc/boot/loader.go
index 239ca5302..eef43b9df 100644
--- a/runsc/boot/loader.go
+++ b/runsc/boot/loader.go
@@ -997,7 +997,7 @@ func (l *Loader) signalProcess(cid string, tgid kernel.ThreadID, signo int32) er
 	execTG, _, err := l.threadGroupFromID(execID{cid: cid, pid: tgid})
 	if err == nil {
 		// Send signal directly to the identified process.
-		return execTG.SendSignal(&arch.SignalInfo{Signo: signo})
+		return l.k.SendExternalSignalThreadGroup(execTG, &arch.SignalInfo{Signo: signo})
 	}
 
 	// The caller may be signaling a process not started directly via exec.
@@ -1014,7 +1014,7 @@ func (l *Loader) signalProcess(cid string, tgid kernel.ThreadID, signo int32) er
 	if tg.Leader().ContainerID() != cid {
 		return fmt.Errorf("process %d is part of a different container: %q", tgid, tg.Leader().ContainerID())
 	}
-	return tg.SendSignal(&arch.SignalInfo{Signo: signo})
+	return l.k.SendExternalSignalThreadGroup(tg, &arch.SignalInfo{Signo: signo})
 }
 
 func (l *Loader) signalForegrondProcessGroup(cid string, tgid kernel.ThreadID, signo int32) error {
@@ -1032,7 +1032,7 @@ func (l *Loader) signalForegrondProcessGroup(cid string, tgid kernel.ThreadID, s
 		// No foreground process group has been set. Signal the
 		// original thread group.
 		log.Warningf("No foreground process group for container %q and PID %d. Sending signal directly to PID %d.", cid, tgid, tgid)
-		return tg.SendSignal(&arch.SignalInfo{Signo: signo})
+		return l.k.SendExternalSignalThreadGroup(tg, &arch.SignalInfo{Signo: signo})
 	}
 	// Send the signal to all processes in the process group.
 	var lastErr error
@@ -1040,7 +1040,7 @@ func (l *Loader) signalForegrondProcessGroup(cid string, tgid kernel.ThreadID, s
 		if tg.ProcessGroup() != pg {
 			continue
 		}
-		if err := tg.SendSignal(&arch.SignalInfo{Signo: signo}); err != nil {
+		if err := l.k.SendExternalSignalThreadGroup(tg, &arch.SignalInfo{Signo: signo}); err != nil {
 			lastErr = err
 		}
 	}