runsc fsgofer: Support dynamic serving of filesystems.

When multiple containers run inside a sentry, each container has its own root
filesystem and set of mounts. Containers are also added after sentry boot rather
than all configured and known at boot time.

The fsgofer needs to be able to serve the root filesystem of each container.
Thus, it must be possible to add filesystems after the fsgofer has already
started.

This change:
* Creates a URPC endpoint within the gofer process that listens for requests to
  serve new content.
* Enables the sentry, when starting a new container, to add the new container's
  filesystem.
* Mounts those new filesystems at separate roots within the sentry.

PiperOrigin-RevId: 208903248
Change-Id: Ifa91ec9c8caf5f2f0a9eead83c4a57090ce92068

1 files changed, 17 insertions, 2 deletions

diff --git a/runsc/boot/controller.go b/runsc/boot/controller.go
index fc6ea326a..69e88d8e0 100644
--- a/runsc/boot/controller.go
+++ b/runsc/boot/controller.go
@@ -17,6 +17,7 @@ package boot
 import (
 	"errors"
 	"fmt"
+	"path"
 
 	specs "github.com/opencontainers/runtime-spec/specs-go"
 	"gvisor.googlesource.com/gvisor/pkg/control/server"
@@ -181,11 +182,15 @@ 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.
+	urpc.FilePayload
 }
 
 // Start runs a created container within a sandbox.
 func (cm *containerManager) Start(args *StartArgs, _ *struct{}) error {
-	log.Debugf("containerManager.Start")
+	log.Debugf("containerManager.Start: %+v", args)
 
 	// Validate arguments.
 	if args == nil {
@@ -200,8 +205,18 @@ func (cm *containerManager) Start(args *StartArgs, _ *struct{}) error {
 	if args.CID == "" {
 		return errors.New("start argument missing container ID")
 	}
+	// Prevent CIDs containing ".." from confusing the sentry when creating
+	// /containers/<cid> directory.
+	// TODO: Once we have multiple independant roots, this
+	// check won't be necessary.
+	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) != 1 {
+		return fmt.Errorf("start arguments must contain one file for the container root")
+	}
 
-	tgid, err := cm.l.startContainer(args, cm.l.k)
+	tgid, err := cm.l.startContainer(cm.l.k, args.Spec, args.Conf, args.CID, args.FilePayload.Files[0])
 	if err != nil {
 		return err
 	}