ipc: umount all mounts before removing temp dirs

This is needed if unshare(CLONE_NEWNS) is not implemented.
Otherwise, os.RemoveAll fails.

fileutil/fileutil.go

@@ -12,6 +12,7 @@ import (
 	"strconv"
 	"sync"
 	"syscall"
+	"unsafe"
 )
 
 var copyMu sync.Mutex
@@ -103,3 +104,16 @@ func ProcessTempDir(where string) (string, int, error) {
 	}
 	return "", 0, fmt.Errorf("too many live instances")
 }
+
+// UmountAll recurusively unmounts all mounts in dir.
+func UmountAll(dir string) {
+	files, _ := ioutil.ReadDir(dir)
+	for _, f := range files {
+		name := filepath.Join(dir, f.Name())
+		if f.IsDir() {
+			UmountAll(name)
+		}
+		fn := []byte(name + "\x00")
+		syscall.Syscall(syscall.SYS_UMOUNT2, uintptr(unsafe.Pointer(&fn[0])), syscall.MNT_FORCE, 0)
+	}
+}

ipc/ipc.go

@@ -16,6 +16,7 @@ import (
 	"syscall"
 	"time"
 
+	"github.com/google/syzkaller/fileutil"
 	"github.com/google/syzkaller/prog"
 )
 
@@ -356,6 +357,7 @@ func (c *command) close() {
 		c.kill()
 		c.cmd.Wait()
 	}
+	fileutil.UmountAll(c.dir)
 	os.RemoveAll(c.dir)
 	if c.rp != nil {
 		c.rp.Close()
@@ -400,6 +402,7 @@ func (c *command) exec() (output, strace []byte, failed, hanged bool, err0 error
 	//!!! handle c.rp overflow
 	_, readErr := c.inrp.Read(tmp[:])
 	close(done)
+	fileutil.UmountAll(c.dir)
 	os.RemoveAll(c.dir)
 	if err := os.Mkdir(c.dir, 0777); err != nil {
 		<-hang