Drop return from SendExternalSignal

SendExternalSignal is no longer called before CreateProcess, so it can
enforce this simplified precondition.

StartForwarding, and after Kernel.Start.

PiperOrigin-RevId: 201591170
Change-Id: Ib7022ef7895612d7d82a00942ab59fa433c4d6e9

3 files changed, 19 insertions, 15 deletions

diff --git a/pkg/sentry/kernel/kernel.go b/pkg/sentry/kernel/kernel.go
index a17148af1..5662b8f08 100644
--- a/pkg/sentry/kernel/kernel.go
+++ b/pkg/sentry/kernel/kernel.go
@@ -760,12 +760,11 @@ func (k *Kernel) Unpause() {
 //
 // context is used only for debugging to describe how the signal was received.
 //
-// Returns false if signal could not be sent because the Kernel is not fully
-// initialized yet.
-func (k *Kernel) SendExternalSignal(info *arch.SignalInfo, context string) bool {
+// Preconditions: Kernel must have an init process.
+func (k *Kernel) SendExternalSignal(info *arch.SignalInfo, context string) {
 	k.extMu.Lock()
 	defer k.extMu.Unlock()
-	return k.sendExternalSignal(info, context)
+	k.sendExternalSignal(info, context)
 }
 
 // FeatureSet returns the FeatureSet.
diff --git a/pkg/sentry/kernel/signal.go b/pkg/sentry/kernel/signal.go
index 8edd05cdf..e3a2a777a 100644
--- a/pkg/sentry/kernel/signal.go
+++ b/pkg/sentry/kernel/signal.go
@@ -15,6 +15,8 @@
 package kernel
 
 import (
+	"fmt"
+
 	"gvisor.googlesource.com/gvisor/pkg/abi/linux"
 	"gvisor.googlesource.com/gvisor/pkg/log"
 	"gvisor.googlesource.com/gvisor/pkg/sentry/arch"
@@ -33,13 +35,11 @@ const SignalPanic = linux.SIGUSR2
 //
 // context is used only for debugging to differentiate these cases.
 //
-// Returns false if signal could not be sent because the Kernel is not fully
-// initialized yet.
-func (k *Kernel) sendExternalSignal(info *arch.SignalInfo, context string) bool {
+// Preconditions: Kernel must have an init process.
+func (k *Kernel) sendExternalSignal(info *arch.SignalInfo, context string) {
 	switch linux.Signal(info.Signo) {
 	case platform.SignalInterrupt:
 		// Assume that a call to platform.Context.Interrupt() misfired.
-		return true
 
 	case SignalPanic:
 		// SignalPanic is also specially handled in sentry setup to ensure that
@@ -50,13 +50,10 @@ func (k *Kernel) sendExternalSignal(info *arch.SignalInfo, context string) bool
 	default:
 		log.Infof("Received external signal %d in %s context", info.Signo, context)
 		if k.globalInit == nil {
-			log.Warningf("Received external signal %d before init created", info.Signo)
-			return false
+			panic(fmt.Sprintf("Received external signal %d before init created", info.Signo))
 		}
 		k.globalInit.SendSignal(info)
 	}
-
-	return true
 }
 
 // sigPriv returns a SignalInfo representing a signal sent by the sentry. (The
diff --git a/pkg/sentry/sighandling/sighandling.go b/pkg/sentry/sighandling/sighandling.go
index ef6f7f617..25295440c 100644
--- a/pkg/sentry/sighandling/sighandling.go
+++ b/pkg/sentry/sighandling/sighandling.go
@@ -16,6 +16,7 @@
 package sighandling
 
 import (
+	"fmt"
 	"os"
 	"os/signal"
 	"reflect"
@@ -65,7 +66,9 @@ func forwardSignals(k *kernel.Kernel, sigchans []chan os.Signal, start, stop cha
 
 		// Otherwise, it was a signal on channel N. Index 0 represents the stop
 		// channel, so index N represents the channel for signal N.
-		if !started || !k.SendExternalSignal(&arch.SignalInfo{Signo: int32(index)}, "sentry") {
+		signal := linux.Signal(index)
+
+		if !started {
 			// Kernel is not ready to receive signals.
 			//
 			// Kill ourselves if this signal would have killed the
@@ -78,11 +81,16 @@ func forwardSignals(k *kernel.Kernel, sigchans []chan os.Signal, start, stop cha
 			// TODO: Convert Go's runtime.raise from
 			// tkill to tgkill so PrepareForwarding doesn't need to
 			// be called until after filter installation.
-			switch linux.Signal(index) {
+			switch signal {
 			case linux.SIGHUP, linux.SIGINT, linux.SIGTERM:
-				dieFromSignal(linux.Signal(index))
+				dieFromSignal(signal)
+				panic(fmt.Sprintf("Failed to die from signal %d", signal))
+			default:
+				continue
 			}
 		}
+
+		k.SendExternalSignal(&arch.SignalInfo{Signo: int32(signal)}, "sentry")
 	}
 
 	// Close all individual channels.