runsc: Fix stdin/stdout/stderr in multi-container mode.

The issue with the previous change was that the stdin/stdout/stderr passed to
the sentry were dup'd by host.ImportFile. This left a dangling FD that by never
closing caused containerd to timeout waiting on container stop.

PiperOrigin-RevId: 213753032
Change-Id: Ia5e4c0565c42c8610d3b59f65599a5643b0901e4

4 files changed, 44 insertions, 23 deletions

diff --git a/runsc/boot/controller.go b/runsc/boot/controller.go
index b4594c8b0..ddba117c6 100644
--- a/runsc/boot/controller.go
+++ b/runsc/boot/controller.go
@@ -193,8 +193,10 @@ type StartArgs struct {
 	// CID is the ID of the container to start.
 	CID string
 
-	// FilePayload contains the file descriptor over which the sandbox will
-	// request files from its root filesystem.
+	// FilePayload contains, in order:
+	//   * stdin, stdout, and stderr.
+	//   * the file descriptor over which the sandbox will
+	//     request files from its root filesystem.
 	urpc.FilePayload
 }
 
@@ -222,8 +224,8 @@ func (cm *containerManager) Start(args *StartArgs, _ *struct{}) error {
 	if path.Clean(args.CID) != args.CID {
 		return fmt.Errorf("container ID shouldn't contain directory traversals such as \"..\": %q", args.CID)
 	}
-	if len(args.FilePayload.Files) == 0 {
-		return fmt.Errorf("start arguments must contain at least one file for the container root")
+	if len(args.FilePayload.Files) < 4 {
+		return fmt.Errorf("start arguments must contain stdin, stderr, and stdout followed by at least one file for the container root gofer")
 	}
 
 	err := cm.l.startContainer(cm.l.k, args.Spec, args.Conf, args.CID, args.FilePayload.Files)
@@ -408,7 +410,7 @@ func (cm *containerManager) Restore(o *RestoreOpts, _ *struct{}) error {
 	cm.l.k = k
 
 	// Set up the restore environment.
-	fds := &fdDispenser{fds: cm.l.ioFDs}
+	fds := &fdDispenser{fds: cm.l.goferFDs}
 	renv, err := createRestoreEnvironment(cm.l.spec, cm.l.conf, fds)
 	if err != nil {
 		return fmt.Errorf("error creating RestoreEnvironment: %v", err)
diff --git a/runsc/boot/fds.go b/runsc/boot/fds.go
index 9de5a78b1..92d641b68 100644
--- a/runsc/boot/fds.go
+++ b/runsc/boot/fds.go
@@ -16,7 +16,6 @@ package boot
 
 import (
 	"fmt"
-	"syscall"
 
 	"gvisor.googlesource.com/gvisor/pkg/sentry/context"
 	"gvisor.googlesource.com/gvisor/pkg/sentry/fs"
@@ -28,15 +27,20 @@ import (
 
 // createFDMap creates an fd map that contains stdin, stdout, and stderr. If
 // console is true, then ioctl calls will be passed through to the host fd.
-func createFDMap(ctx context.Context, k *kernel.Kernel, l *limits.LimitSet, console bool) (*kernel.FDMap, error) {
+// Upon success, createFDMap dups then closes stdioFDs.
+func createFDMap(ctx context.Context, k *kernel.Kernel, l *limits.LimitSet, console bool, stdioFDs []int) (*kernel.FDMap, error) {
+	if len(stdioFDs) != 3 {
+		return nil, fmt.Errorf("stdioFDs should contain exactly 3 FDs (stdin, stdout, and stderr), but %d FDs received", len(stdioFDs))
+	}
+
 	fdm := k.NewFDMap()
 	defer fdm.DecRef()
 
 	// Maps sandbox fd to host fd.
 	fdMap := map[int]int{
-		0: syscall.Stdin,
-		1: syscall.Stdout,
-		2: syscall.Stderr,
+		0: stdioFDs[0],
+		1: stdioFDs[1],
+		2: stdioFDs[2],
 	}
 	mounter := fs.FileOwnerFromContext(ctx)
 
diff --git a/runsc/boot/fs.go b/runsc/boot/fs.go
index 110f67de8..a97a4a3da 100644
--- a/runsc/boot/fs.go
+++ b/runsc/boot/fs.go
@@ -82,7 +82,7 @@ func (f *fdDispenser) empty() bool {
 
 // createMountNamespace creates a mount namespace containing the root filesystem
 // and all mounts. 'rootCtx' is used to walk directories to find mount points.
-func createMountNamespace(userCtx context.Context, rootCtx context.Context, spec *specs.Spec, conf *Config, ioFDs []int) (*fs.MountNamespace, error) {
+func createMountNamespace(userCtx context.Context, rootCtx context.Context, spec *specs.Spec, conf *Config, goferFDs []int) (*fs.MountNamespace, error) {
 	mounts := compileMounts(spec)
 	if conf.MultiContainer {
 		// Create a tmpfs mount where we create and mount a root filesystem for
@@ -92,7 +92,7 @@ func createMountNamespace(userCtx context.Context, rootCtx context.Context, spec
 			Destination: ChildContainersDir,
 		})
 	}
-	fds := &fdDispenser{fds: ioFDs}
+	fds := &fdDispenser{fds: goferFDs}
 	rootInode, err := createRootMount(rootCtx, spec, conf, fds, mounts)
 	if err != nil {
 		return nil, fmt.Errorf("failed to create root mount: %v", err)
@@ -587,14 +587,14 @@ func subtargets(root string, mnts []specs.Mount) []string {
 }
 
 // setFileSystemForProcess is used to set up the file system and amend the procArgs accordingly.
-// procArgs are passed by reference and the FDMap field is modified.
-func setFileSystemForProcess(procArgs *kernel.CreateProcessArgs, spec *specs.Spec, conf *Config, ioFDs []int, console bool, creds *auth.Credentials, ls *limits.LimitSet, k *kernel.Kernel, cid string) error {
+// procArgs are passed by reference and the FDMap field is modified. It dups stdioFDs.
+func setFileSystemForProcess(procArgs *kernel.CreateProcessArgs, spec *specs.Spec, conf *Config, stdioFDs, goferFDs []int, console bool, creds *auth.Credentials, ls *limits.LimitSet, k *kernel.Kernel, cid string) error {
 	ctx := procArgs.NewContext(k)
 
 	// Create the FD map, which will set stdin, stdout, and stderr.  If
 	// console is true, then ioctl calls will be passed through to the host
 	// fd.
-	fdm, err := createFDMap(ctx, k, ls, console)
+	fdm, err := createFDMap(ctx, k, ls, console, stdioFDs)
 	if err != nil {
 		return fmt.Errorf("error importing fds: %v", err)
 	}
@@ -618,7 +618,7 @@ func setFileSystemForProcess(procArgs *kernel.CreateProcessArgs, spec *specs.Spe
 	mns := k.RootMountNamespace()
 	if mns == nil {
 		// Create the virtual filesystem.
-		mns, err := createMountNamespace(ctx, rootCtx, spec, conf, ioFDs)
+		mns, err := createMountNamespace(ctx, rootCtx, spec, conf, goferFDs)
 		if err != nil {
 			return fmt.Errorf("error creating mounts: %v", err)
 		}
@@ -630,7 +630,7 @@ func setFileSystemForProcess(procArgs *kernel.CreateProcessArgs, spec *specs.Spe
 
 	// Create the container's root filesystem mount.
 	log.Infof("Creating new process in child container.")
-	fds := &fdDispenser{fds: append([]int{}, ioFDs...)}
+	fds := &fdDispenser{fds: append([]int{}, goferFDs...)}
 	rootInode, err := createRootMount(rootCtx, spec, conf, fds, nil)
 	if err != nil {
 		return fmt.Errorf("error creating filesystem for container: %v", err)
diff --git a/runsc/boot/loader.go b/runsc/boot/loader.go
index f906c9f95..e47eced18 100644
--- a/runsc/boot/loader.go
+++ b/runsc/boot/loader.go
@@ -78,8 +78,11 @@ type Loader struct {
 
 	watchdog *watchdog.Watchdog
 
-	// ioFDs are the FDs that attach the sandbox to the gofers.
-	ioFDs []int
+	// stdioFDs contains stdin, stdout, and stderr.
+	stdioFDs []int
+
+	// goferFDs are the FDs that attach the sandbox to the gofers.
+	goferFDs []int
 
 	// spec is the base configuration for the root container.
 	spec *specs.Spec
@@ -139,7 +142,7 @@ func init() {
 
 // New initializes a new kernel loader configured by spec.
 // New also handles setting up a kernel for restoring a container.
-func New(spec *specs.Spec, conf *Config, controllerFD, deviceFD int, ioFDs []int, console bool) (*Loader, error) {
+func New(spec *specs.Spec, conf *Config, controllerFD, deviceFD int, goferFDs []int, console bool) (*Loader, error) {
 	if err := usage.Init(); err != nil {
 		return nil, fmt.Errorf("Error setting up memory usage: %v", err)
 	}
@@ -278,7 +281,8 @@ func New(spec *specs.Spec, conf *Config, controllerFD, deviceFD int, ioFDs []int
 		conf:                  conf,
 		console:               console,
 		watchdog:              watchdog,
-		ioFDs:                 ioFDs,
+		stdioFDs:              []int{syscall.Stdin, syscall.Stdout, syscall.Stderr},
+		goferFDs:              goferFDs,
 		spec:                  spec,
 		startSignalForwarding: startSignalForwarding,
 		rootProcArgs:          procArgs,
@@ -390,7 +394,8 @@ func (l *Loader) run() error {
 			&l.rootProcArgs,
 			l.spec,
 			l.conf,
-			l.ioFDs,
+			l.stdioFDs,
+			l.goferFDs,
 			l.console,
 			l.rootProcArgs.Credentials,
 			l.rootProcArgs.Limits,
@@ -474,11 +479,14 @@ func (l *Loader) startContainer(k *kernel.Kernel, spec *specs.Spec, conf *Config
 		ioFDs = append(ioFDs, fd)
 	}
 
+	stdioFDs := ioFDs[:3]
+	goferFDs := ioFDs[3:]
 	if err := setFileSystemForProcess(
 		&procArgs,
 		spec,
 		conf,
-		ioFDs,
+		stdioFDs,
+		goferFDs,
 		false,
 		creds,
 		procArgs.Limits,
@@ -487,6 +495,13 @@ func (l *Loader) startContainer(k *kernel.Kernel, spec *specs.Spec, conf *Config
 		return fmt.Errorf("failed to create new process: %v", err)
 	}
 
+	// setFileSystemForProcess dup'd stdioFDs, so we can close them.
+	for i, fd := range stdioFDs {
+		if err := syscall.Close(fd); err != nil {
+			return fmt.Errorf("failed to close stdioFD #%d: %v", i, fd)
+		}
+	}
+
 	ctx := procArgs.NewContext(l.k)
 	mns := k.RootMountNamespace()
 	if err := setExecutablePath(ctx, mns, &procArgs); err != nil {