runsc: Pass log and config files to sandbox process by FD.

This is a prereq for running the sandbox process as user "nobody", when it may
not have permissions to open these files.

Instead, we must open then before starting the sandbox process, and pass them
by FD.

The specutils.ReadSpecFromFile method was fixed to always seek to the beginning
of the file before reading. This allows Files from the same FD to be read
multiple times, as we do in the boot command when the apply-caps flag is set.

Tested with --network=host.

PiperOrigin-RevId: 211570647
Change-Id: I685be0a290aa7f70731ebdce82ebc0ebcc9d475c

1 files changed, 60 insertions, 19 deletions

diff --git a/runsc/sandbox/sandbox.go b/runsc/sandbox/sandbox.go
index f14a2f8c9..e0fadefcd 100644
--- a/runsc/sandbox/sandbox.go
+++ b/runsc/sandbox/sandbox.go
@@ -233,34 +233,70 @@ func (s *Sandbox) createSandboxProcess(spec *specs.Spec, conf *boot.Config, bund
 	// starts at 3 because 0, 1, and 2 are taken by stdin/out/err.
 	nextFD := 3
 
-	// Create control server socket here and donate FD to child process because
-	// it may be in a different network namespace and won't be reachable from
-	// outside.
-	addr := boot.ControlSocketAddr(s.ID)
-	fd, err := server.CreateSocket(addr)
-	log.Infof("Creating sandbox process with addr: %s", addr[1:]) // skip "\00".
-	if err != nil {
-		return fmt.Errorf("error creating control server socket for sandbox %q: %v", s.ID, err)
-	}
-
-	consoleEnabled := consoleSocket != ""
-
 	binPath, err := specutils.BinPath()
 	if err != nil {
 		return err
 	}
 	cmd := exec.Command(binPath, conf.ToFlags()...)
 	cmd.SysProcAttr = &syscall.SysProcAttr{}
-	cmd.Args = append(cmd.Args,
-		"boot",
-		"--bundle", bundleDir,
-		"--controller-fd="+strconv.Itoa(nextFD),
-		"--console="+strconv.FormatBool(consoleEnabled))
-	nextFD++
 
-	controllerFile := os.NewFile(uintptr(fd), "control_server_socket")
+	// Open the log files to pass to the sandbox as FDs.
+	//
+	// These flags must come BEFORE the "boot" command in cmd.Args.
+	if conf.LogFilename != "" {
+		logFile, err := os.OpenFile(conf.LogFilename, os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0644)
+		if err != nil {
+			return fmt.Errorf("error opening log file %q: %v", conf.LogFilename, err)
+		}
+		defer logFile.Close()
+		cmd.ExtraFiles = append(cmd.ExtraFiles, logFile)
+		cmd.Args = append(cmd.Args, "--log-fd="+strconv.Itoa(nextFD))
+		nextFD++
+	}
+	if conf.DebugLogDir != "" {
+		debugLogFile, err := specutils.DebugLogFile(conf.DebugLogDir, "boot")
+		if err != nil {
+			return fmt.Errorf("error opening debug log file in %q: %v", conf.DebugLogDir, err)
+		}
+		defer debugLogFile.Close()
+		cmd.ExtraFiles = append(cmd.ExtraFiles, debugLogFile)
+		cmd.Args = append(cmd.Args, "--debug-log-fd="+strconv.Itoa(nextFD))
+		nextFD++
+	}
+
+	// Add the "boot" command to the args.
+	//
+	// All flags after this must be for the boot command
+	cmd.Args = append(cmd.Args, "boot", "--bundle="+bundleDir)
+
+	consoleEnabled := consoleSocket != ""
+	cmd.Args = append(cmd.Args, "--console="+strconv.FormatBool(consoleEnabled))
+
+	// Create a socket for the control server and donate it to the sandbox.
+	addr := boot.ControlSocketAddr(s.ID)
+	sockFD, err := server.CreateSocket(addr)
+	log.Infof("Creating sandbox process with addr: %s", addr[1:]) // skip "\00".
+	if err != nil {
+		return fmt.Errorf("error creating control server socket for sandbox %q: %v", s.ID, err)
+	}
+	controllerFile := os.NewFile(uintptr(sockFD), "control_server_socket")
 	defer controllerFile.Close()
 	cmd.ExtraFiles = append(cmd.ExtraFiles, controllerFile)
+	cmd.Args = append(cmd.Args, "--controller-fd="+strconv.Itoa(nextFD))
+	nextFD++
+
+	// Open the spec file to donate to the sandbox.
+	if conf.SpecFile == "" {
+		return fmt.Errorf("conf.SpecFile must be set")
+	}
+	specFile, err := os.Open(conf.SpecFile)
+	if err != nil {
+		return fmt.Errorf("error opening spec file %q: %v", conf.SpecFile, err)
+	}
+	defer specFile.Close()
+	cmd.ExtraFiles = append(cmd.ExtraFiles, specFile)
+	cmd.Args = append(cmd.Args, "--spec-fd="+strconv.Itoa(nextFD))
+	nextFD++
 
 	// If there is a gofer, sends all socket ends to the sandbox.
 	for _, f := range ioFiles {
@@ -357,6 +393,11 @@ func (s *Sandbox) createSandboxProcess(spec *specs.Spec, conf *boot.Config, bund
 		nss = append(nss, specs.LinuxNamespace{Type: specs.UserNamespace})
 	}
 
+	// Log the fds we are donating to the sandbox process.
+	for i, f := range cmd.ExtraFiles {
+		log.Debugf("Donating FD %d: %q", i+3, f.Name())
+	}
+
 	log.Debugf("Starting sandbox: %s %v", binPath, cmd.Args)
 	if err := specutils.StartInNS(cmd, nss); err != nil {
 		return err