diff options
Diffstat (limited to 'runsc/cmd')
| -rw-r--r-- | runsc/cmd/chroot.go | 45 | ||||
| -rw-r--r-- | runsc/cmd/gofer.go | 69 |
2 files changed, 80 insertions, 34 deletions
diff --git a/runsc/cmd/chroot.go b/runsc/cmd/chroot.go index c1acbf26b..ed1dafef1 100644 --- a/runsc/cmd/chroot.go +++ b/runsc/cmd/chroot.go @@ -36,6 +36,29 @@ func mountInChroot(chroot, src, dst, typ string, flags uint32) error { return nil } +func pivotRoot(root string) error { + if err := os.Chdir(root); err != nil { + return fmt.Errorf("error changing working directory: %v", err) + } + // pivot_root(new_root, put_old) moves the root filesystem (old_root) + // of the calling process to the directory put_old and makes new_root + // the new root filesystem of the calling process. + // + // pivot_root(".", ".") makes a mount of the working directory the new + // root filesystem, so it will be moved in "/" and then the old_root + // will be moved to "/" too. The parent mount of the old_root will be + // new_root, so after umounting the old_root, we will see only + // the new_root in "/". + if err := syscall.PivotRoot(".", "."); err != nil { + return fmt.Errorf("error changing root filesystem: %v", err) + } + + if err := syscall.Unmount(".", syscall.MNT_DETACH); err != nil { + return fmt.Errorf("error umounting the old root file system: %v", err) + } + return nil +} + // setUpChroot creates an empty directory with runsc mounted at /runsc and proc // mounted at /proc. func setUpChroot(pidns bool) error { @@ -66,29 +89,9 @@ func setUpChroot(pidns bool) error { } } - if err := os.Chdir(chroot); err != nil { - return fmt.Errorf("error changing working directory: %v", err) - } - if err := syscall.Mount("", chroot, "", syscall.MS_REMOUNT|syscall.MS_RDONLY|syscall.MS_BIND, ""); err != nil { return fmt.Errorf("error remounting chroot in read-only: %v", err) } - // pivot_root(new_root, put_old) moves the root filesystem (old_root) - // of the calling process to the directory put_old and makes new_root - // the new root filesystem of the calling process. - // - // pivot_root(".", ".") makes a mount of the working directory the new - // root filesystem, so it will be moved in "/" and then the old_root - // will be moved to "/" too. The parent mount of the old_root will be - // new_root, so after umounting the old_root, we will see only - // the new_root in "/". - if err := syscall.PivotRoot(".", "."); err != nil { - return fmt.Errorf("error changing root filesystem: %v", err) - } - if err := syscall.Unmount(".", syscall.MNT_DETACH); err != nil { - return fmt.Errorf("error umounting the old root file system: %v", err) - } - - return nil + return pivotRoot(chroot) } diff --git a/runsc/cmd/gofer.go b/runsc/cmd/gofer.go index 43286a2e5..6f9711518 100644 --- a/runsc/cmd/gofer.go +++ b/runsc/cmd/gofer.go @@ -26,6 +26,7 @@ import ( "gvisor.googlesource.com/gvisor/pkg/log" "gvisor.googlesource.com/gvisor/pkg/p9" "gvisor.googlesource.com/gvisor/pkg/unet" + "gvisor.googlesource.com/gvisor/runsc/boot" "gvisor.googlesource.com/gvisor/runsc/fsgofer" "gvisor.googlesource.com/gvisor/runsc/fsgofer/filter" "gvisor.googlesource.com/gvisor/runsc/specutils" @@ -54,8 +55,10 @@ type Gofer struct { bundleDir string ioFDs intFlags applyCaps bool + setUpRoot bool panicOnWrite bool + specFD int } // Name implements subcommands.Command. @@ -79,43 +82,83 @@ func (g *Gofer) SetFlags(f *flag.FlagSet) { 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") + f.BoolVar(&g.setUpRoot, "setup-root", true, "if true, set up an empty root for the process") + f.IntVar(&g.specFD, "spec-fd", -1, "required fd with the container spec") } // Execute implements subcommands.Command. func (g *Gofer) Execute(_ context.Context, f *flag.FlagSet, args ...interface{}) subcommands.ExitStatus { - if g.bundleDir == "" || len(g.ioFDs) < 1 { + if g.bundleDir == "" || len(g.ioFDs) < 1 || g.specFD < 0 { f.Usage() return subcommands.ExitUsageError } + specFile := os.NewFile(uintptr(g.specFD), "spec file") + defer specFile.Close() + spec, err := specutils.ReadSpecFromFile(g.bundleDir, specFile) + if err != nil { + Fatalf("reading spec: %v", err) + } + + // Find what path is going to be served by this gofer. + root := spec.Root.Path + + conf := args[0].(*boot.Config) + + if g.setUpRoot && !conf.TestOnlyAllowRunAsCurrentUserWithoutChroot { + // Convert all shared mounts into slave to be sure that nothing will be + // propagated outside of our namespace. + if err := syscall.Mount("", "/", "", syscall.MS_SLAVE|syscall.MS_REC, ""); err != nil { + Fatalf("error converting mounts: %v", err) + } + + // FIXME: runsc can't be re-executed without + // /proc, so we create a tmpfs mount, mount ./proc and ./root + // there, then move this mount to the root and after + // setCapsAndCallSelf, runsc will chroot into /root. + // + // We need a directory to construct a new root and we know that + // runsc can't start without /proc, so we can use it for this. + flags := uintptr(syscall.MS_NOSUID | syscall.MS_NODEV | syscall.MS_NOEXEC) + if err := syscall.Mount("runsc-root", "/proc", "tmpfs", flags, ""); err != nil { + Fatalf("error mounting tmpfs: %v", err) + } + os.Mkdir("/proc/proc", 0755) + os.Mkdir("/proc/root", 0755) + if err := syscall.Mount("runsc-proc", "/proc/proc", "proc", flags|syscall.MS_RDONLY, ""); err != nil { + Fatalf("error mounting proc: %v", err) + } + if err := syscall.Mount(root, "/proc/root", "", syscall.MS_BIND|syscall.MS_REC, ""); err != nil { + Fatalf("error mounting root: %v", err) + } + if err := pivotRoot("/proc"); err != nil { + Fatalf("faild to change the root file system: %v", err) + } + if err := os.Chdir("/"); err != nil { + Fatalf("failed to change working directory") + } + } + if g.applyCaps { // 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") + args = append(args, "--apply-caps=false", "--setup-root=false") if err := setCapsAndCallSelf(args, goferCaps); err != nil { Fatalf("Unable to apply caps: %v", err) } panic("unreachable") } - specFile, err := specutils.OpenCleanSpec(g.bundleDir) - if err != nil { - Fatalf("opening spec: %v", err) - } - spec, err := specutils.ReadSpecFromFile(g.bundleDir, specFile) - specFile.Close() - if err != nil { - Fatalf("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 := spec.Root.Path + if !conf.TestOnlyAllowRunAsCurrentUserWithoutChroot { + root = "/root" + } if err := syscall.Chroot(root); err != nil { Fatalf("failed to chroot to %q: %v", root, err) } |