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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"
"path"
"sync"
"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/pkg/unet"
"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
panicOnWrite bool
}
// 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.BoolVar(&g.panicOnWrite, "panic-on-write", false, "if true, panics on attempts to write to RO mounts. RW mounts are unnaffected")
}
// Execute implements subcommands.Command.
func (g *Gofer) Execute(_ context.Context, f *flag.FlagSet, args ...interface{}) subcommands.ExitStatus {
if g.bundleDir == "" || len(g.ioFDs) < 1 {
f.Usage()
return subcommands.ExitUsageError
}
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")
}
spec, err := specutils.ReadSpec(g.bundleDir)
if err != nil {
Fatalf("error reading spec: %v", err)
}
specutils.LogSpec(spec)
// 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)
// Find what path is going to be served by this gofer.
root := absPath(g.bundleDir, spec.Root.Path)
if err := syscall.Chroot(root); err != nil {
Fatalf("failed to chroot to %q: %v", root, err)
}
if err := syscall.Chdir("/"); err != nil {
Fatalf("failed to change working dir: %v", err)
}
log.Infof("Process chroot'd to %q", root)
// Start with root mount, then add any other additional mount as needed.
ats := make([]p9.Attacher, 0, len(spec.Mounts)+1)
ats = append(ats, fsgofer.NewAttachPoint("/", fsgofer.Config{
ROMount: spec.Root.Readonly,
PanicOnWrite: g.panicOnWrite,
// 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 (ro: %t)", "/", root, g.ioFDs[0], spec.Root.Readonly)
mountIdx := 1 // first one is the root
for _, m := range spec.Mounts {
if specutils.Is9PMount(m) {
if !path.IsAbs(m.Destination) {
Fatalf("destination must be absolute path: %v", m.Destination)
}
cfg := fsgofer.Config{
ROMount: isReadonlyMount(m.Options),
PanicOnWrite: g.panicOnWrite,
LazyOpenForWrite: false,
}
ats = append(ats, fsgofer.NewAttachPoint(m.Destination, cfg))
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 on FD %d (ro: %t)", m.Destination, g.ioFDs[mountIdx], cfg.ROMount)
mountIdx++
}
}
if mountIdx != len(g.ioFDs) {
Fatalf("too many FDs passed for mounts. mounts: %d, FDs: %d", mountIdx, len(g.ioFDs))
}
runServers(ats, g.ioFDs)
return subcommands.ExitSuccess
}
func runServers(ats []p9.Attacher, ioFDs []int) {
// Run the loops and wait for all to exit.
var wg sync.WaitGroup
for i, ioFD := range ioFDs {
wg.Add(1)
go func(ioFD int, at p9.Attacher) {
socket, err := unet.NewSocket(ioFD)
if err != nil {
Fatalf("err creating server on FD %d: %v", ioFD, err)
}
s := p9.NewServer(at)
if err := s.Handle(socket); err != nil {
Fatalf("P9 server returned error. Gofer is shutting down. FD: %d, err: %v", ioFD, err)
}
wg.Done()
}(ioFD, ats[i])
}
wg.Wait()
log.Infof("All 9P servers exited.")
}
func isReadonlyMount(opts []string) bool {
for _, o := range opts {
if o == "ro" {
return true
}
}
return false
}
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