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// Copyright 2018 Google Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package cmd
import (
"os"
"syscall"
"context"
"flag"
"github.com/google/subcommands"
specs "github.com/opencontainers/runtime-spec/specs-go"
"gvisor.googlesource.com/gvisor/pkg/log"
"gvisor.googlesource.com/gvisor/pkg/p9"
"gvisor.googlesource.com/gvisor/runsc/fsgofer"
"gvisor.googlesource.com/gvisor/runsc/specutils"
)
// Gofer implements subcommands.Command for the "gofer" command, which starts a
// filesystem gofer. This command should not be called directly.
type Gofer struct {
bundleDir string
ioFDs intFlags
applyCaps bool
// controllerFD is the file descriptor of a stream socket for the
// control server that is donated to this process.
controllerFD int
}
// Name implements subcommands.Command.
func (*Gofer) Name() string {
return "gofer"
}
// Synopsis implements subcommands.Command.
func (*Gofer) Synopsis() string {
return "launch a gofer process that serves files over 9P protocol (internal use only)"
}
// Usage implements subcommands.Command.
func (*Gofer) Usage() string {
return `gofer [flags]`
}
// SetFlags implements subcommands.Command.
func (g *Gofer) SetFlags(f *flag.FlagSet) {
f.StringVar(&g.bundleDir, "bundle", "", "path to the root of the bundle directory, defaults to the current directory")
f.Var(&g.ioFDs, "io-fds", "list of FDs to connect 9P servers. They must follow this order: root first, then mounts as defined in the spec")
f.BoolVar(&g.applyCaps, "apply-caps", true, "if true, apply capabilities to restrict what the Gofer process can do")
f.IntVar(&g.controllerFD, "controller-fd", -1, "required FD of a stream socket for the control server that must be donated to this process")
}
// Execute implements subcommands.Command.
func (g *Gofer) Execute(_ context.Context, f *flag.FlagSet, args ...interface{}) subcommands.ExitStatus {
if g.bundleDir == "" || len(g.ioFDs) < 1 || g.controllerFD == -1 {
f.Usage()
return subcommands.ExitUsageError
}
// fsgofer should run with a umask of 0, because we want to preserve file
// modes exactly as sent by the sandbox, which will have applied its own umask.
syscall.Umask(0)
spec, err := specutils.ReadSpec(g.bundleDir)
if err != nil {
Fatalf("error reading spec: %v", err)
}
if g.applyCaps {
// Minimal set of capabilities needed by the Gofer to operate on files.
caps := []string{
"CAP_CHOWN",
"CAP_DAC_OVERRIDE",
"CAP_DAC_READ_SEARCH",
"CAP_FOWNER",
"CAP_FSETID",
}
lc := &specs.LinuxCapabilities{
Bounding: caps,
Effective: caps,
Permitted: caps,
}
// Disable caps when calling myself again.
// Note: minimal argument handling for the default case to keep it simple.
args := os.Args
args = append(args, "--apply-caps=false")
if err := setCapsAndCallSelf(args, lc); err != nil {
Fatalf("Unable to apply caps: %v", err)
}
panic("unreachable")
}
specutils.LogSpec(spec)
// Start with root mount, then add any other addition mount as needed.
ats := make([]p9.Attacher, 0, len(spec.Mounts)+1)
p := absPath(g.bundleDir, spec.Root.Path)
ats = append(ats, fsgofer.NewAttachPoint(p, fsgofer.Config{
ROMount: spec.Root.Readonly,
// Docker uses overlay2 by default for the root mount, and overlay2 does a copy-up when
// each file is opened as writable. Thus, we open files lazily to avoid copy-up.
LazyOpenForWrite: true,
}))
log.Infof("Serving %q mapped to %q on FD %d", "/", p, g.ioFDs[0])
mountIdx := 1 // first one is the root
for _, m := range spec.Mounts {
if specutils.Is9PMount(m) {
p = absPath(g.bundleDir, m.Source)
ats = append(ats, fsgofer.NewAttachPoint(p, fsgofer.Config{
ROMount: isReadonlyMount(m.Options),
LazyOpenForWrite: false,
}))
if mountIdx >= len(g.ioFDs) {
Fatalf("No FD found for mount. Did you forget --io-fd? mount: %d, %v", len(g.ioFDs), m)
}
log.Infof("Serving %q mapped to %q on FD %d", m.Destination, p, g.ioFDs[mountIdx])
mountIdx++
}
}
if mountIdx != len(g.ioFDs) {
Fatalf("Too many FDs passed for mounts. mounts: %d, FDs: %d", mountIdx, len(g.ioFDs))
}
ctrl, err := fsgofer.NewController(g.controllerFD, g.bundleDir)
if err := ctrl.Serve(ats, g.ioFDs); err != nil {
Fatalf("Failed to serve via P9: %v", err)
}
ctrl.Wait()
return subcommands.ExitSuccess
}
func isReadonlyMount(opts []string) bool {
for _, o := range opts {
if o == "ro" {
return true
}
}
return false
}
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