From 2f93ddbe6276d37b2a348e71868e2e2a25909801 Mon Sep 17 00:00:00 2001
From: Nicolas Lacasse <nlacasse@google.com>
Date: Thu, 10 Aug 2023 15:31:35 -0700
Subject: [PATCH] Create kernel.SendExternalSignalProcessGroup and use it in
 boot/loader.go

This will send a signal to all processes (ThreadGroups) in a ProcessGroup.

PiperOrigin-RevId: 555679773
---
 pkg/sentry/kernel/kernel.go | 22 ++++++++++++++++++++++
 runsc/boot/loader.go        | 14 +++-----------
 2 files changed, 25 insertions(+), 11 deletions(-)

diff --git a/pkg/sentry/kernel/kernel.go b/pkg/sentry/kernel/kernel.go
index 04d241996..34a8efbf1 100644
--- a/pkg/sentry/kernel/kernel.go
+++ b/pkg/sentry/kernel/kernel.go
@@ -1213,6 +1213,7 @@ func (k *Kernel) SendExternalSignal(info *linux.SignalInfo, context string) {
 }
 
 // SendExternalSignalThreadGroup injects a signal into an specific ThreadGroup.
+//
 // This function doesn't skip signals like SendExternalSignal does.
 func (k *Kernel) SendExternalSignalThreadGroup(tg *ThreadGroup, info *linux.SignalInfo) error {
 	k.extMu.Lock()
@@ -1220,6 +1221,27 @@ func (k *Kernel) SendExternalSignalThreadGroup(tg *ThreadGroup, info *linux.Sign
 	return tg.SendSignal(info)
 }
 
+// SendExternalSignalProcessGroup sends a signal to all ThreadGroups in the
+// given process group.
+//
+// This function doesn't skip signals like SendExternalSignal does.
+func (k *Kernel) SendExternalSignalProcessGroup(pg *ProcessGroup, info *linux.SignalInfo) error {
+	k.extMu.Lock()
+	defer k.extMu.Unlock()
+	// If anything goes wrong, we'll return the error, but still try our
+	// best to deliver to other processes in the group.
+	var firstErr error
+	for _, tg := range k.TaskSet().Root.ThreadGroups() {
+		if tg.ProcessGroup() != pg {
+			continue
+		}
+		if err := tg.SendSignal(info); err != nil && firstErr == nil {
+			firstErr = err
+		}
+	}
+	return firstErr
+}
+
 // SendContainerSignal sends the given signal to all processes inside the
 // namespace that match the given container ID.
 func (k *Kernel) SendContainerSignal(cid string, info *linux.SignalInfo) error {
diff --git a/runsc/boot/loader.go b/runsc/boot/loader.go
index 69d25d6c9..4cd3b5273 100644
--- a/runsc/boot/loader.go
+++ b/runsc/boot/loader.go
@@ -1414,23 +1414,15 @@ func (l *Loader) signalForegrondProcessGroup(cid string, tgid kernel.ThreadID, s
 		return fmt.Errorf("no TTY attached")
 	}
 	pg := tty.ForegroundProcessGroup()
+	si := &linux.SignalInfo{Signo: signo}
 	if pg == nil {
 		// 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 l.k.SendExternalSignalThreadGroup(tg, &linux.SignalInfo{Signo: signo})
+		return l.k.SendExternalSignalThreadGroup(tg, si)
 	}
 	// Send the signal to all processes in the process group.
-	var lastErr error
-	for _, tg := range l.k.TaskSet().Root.ThreadGroups() {
-		if tg.ProcessGroup() != pg {
-			continue
-		}
-		if err := l.k.SendExternalSignalThreadGroup(tg, &linux.SignalInfo{Signo: signo}); err != nil {
-			lastErr = err
-		}
-	}
-	return lastErr
+	return l.k.SendExternalSignalProcessGroup(pg, si)
 }
 
 // signalAllProcesses that belong to specified container. It's a noop if the