pkg/ipc: stop reading executor output after it exited

An executor can leak its file descriptor and we can block on reading
from it forever.

Signed-off-by: Andrei Vagin <avagin@google.com>

2 files changed, 35 insertions, 10 deletions

diff --git a/pkg/ipc/ipc.go b/pkg/ipc/ipc.go
index d930b756b..839fdcd4c 100644
--- a/pkg/ipc/ipc.go
+++ b/pkg/ipc/ipc.go
@@ -492,7 +492,7 @@ type command struct {
 	cmd      *exec.Cmd
 	dir      string
 	readDone chan []byte
-	exited   chan struct{}
+	exited   chan error
 	inrp     *os.File
 	outwp    *os.File
 	outmem   []byte
@@ -603,7 +603,6 @@ func makeCommand(pid int, bin []string, config *Config, inFile, outFile *os.File
 	c.outwp = outwp
 
 	c.readDone = make(chan []byte, 1)
-	c.exited = make(chan struct{})
 
 	cmd := osutil.Command(bin[0], bin[1:]...)
 	if inFile != nil && outFile != nil {
@@ -645,7 +644,15 @@ func makeCommand(pid int, bin []string, config *Config, inFile, outFile *os.File
 	if err := cmd.Start(); err != nil {
 		return nil, fmt.Errorf("failed to start executor binary: %v", err)
 	}
+	c.exited = make(chan error, 1)
 	c.cmd = cmd
+	go func(c *command) {
+		err := c.cmd.Wait()
+		c.exited <- err
+		close(c.exited)
+		// Avoid a livelock if cmd.Stderr has been leaked to another alive process.
+		rp.SetDeadline(time.Now().Add(5 * time.Second))
+	}(c)
 	wp.Close()
 	// Note: we explicitly close inwp before calling handshake even though we defer it above.
 	// If we don't do it and executor exits before writing handshake reply,
@@ -725,14 +732,7 @@ func (c *command) handshakeError(err error) error {
 }
 
 func (c *command) wait() error {
-	err := c.cmd.Wait()
-	select {
-	case <-c.exited:
-		// c.exited closed by an earlier call to wait.
-	default:
-		close(c.exited)
-	}
-	return err
+	return <-c.exited
 }
 
 func (c *command) exec(opts *ExecOpts, progData []byte) (output []byte, hanged bool, err0 error) {
diff --git a/pkg/ipc/ipc_priv_test.go b/pkg/ipc/ipc_priv_test.go
new file mode 100644
index 000000000..be164911a
--- /dev/null
+++ b/pkg/ipc/ipc_priv_test.go
@@ -0,0 +1,25 @@
+// Copyright 2022 syzkaller project authors. All rights reserved.
+// Use of this source code is governed by Apache 2 LICENSE that can be found in the LICENSE file.
+
+package ipc
+
+import (
+	"testing"
+)
+
+func TestOutputDeadline(t *testing.T) {
+	// Run the command that leaks stderr to a child process.
+	c, err := makeCommand(1, []string{
+		"sh",
+		"-c",
+		"exec 1>&2; ( sleep 100; echo fail ) & echo done",
+	}, &Config{}, nil, nil, nil, "/tmp")
+	if err != nil {
+		t.Fatal(err)
+	}
+	c.wait()
+	out := <-c.readDone
+	if string(out) != "done\n" {
+		t.Errorf("Unexpected output: '%s'", out)
+	}
+}