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overlay: use idmapped lower layers where supported
use idmapped mounts for the overlay lower layers when the kernel supports them. For each lower directory with ID=0...N-1, it creates a idmapped mount at $GRAPHROOT/overlay/$LAYER/mapped/$ID. The final overlay mount will use these idmapped mounts instead of the original source directory. The upperdir is not idmapped, so files are created with the same IDs used by the user namespace. Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,160 @@ | ||
| //go:build linux | ||
| // +build linux | ||
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| package overlay | ||
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| import ( | ||
| "fmt" | ||
| "io/ioutil" | ||
| "os" | ||
| "syscall" | ||
| "unsafe" | ||
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| "github.com/containers/storage/pkg/idtools" | ||
| "github.com/pkg/errors" | ||
| "golang.org/x/sys/unix" | ||
| ) | ||
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| type attr struct { | ||
| attrSet uint64 | ||
| attrClr uint64 | ||
| propagation uint64 | ||
| userNs uint64 | ||
| } | ||
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| const ( | ||
| // _MOUNT_ATTR_IDMAP - Idmap mount to @userns_fd in struct mount_attr | ||
| _MOUNT_ATTR_IDMAP = 0x00100000 //nolint:golint | ||
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| // _OPEN_TREE_CLONE - Clone the source path mount | ||
| _OPEN_TREE_CLONE = 0x00000001 //nolint:golint | ||
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| // _MOVE_MOUNT_F_EMPTY_PATH - Move the path referenced by the fd | ||
| _MOVE_MOUNT_F_EMPTY_PATH = 0x00000004 //nolint:golint | ||
| ) | ||
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| // openTree is a wrapper for the open_tree syscall | ||
| func openTree(path string, flags int) (fd int, err error) { | ||
| var _p0 *byte | ||
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| if _p0, err = syscall.BytePtrFromString(path); err != nil { | ||
| return 0, err | ||
| } | ||
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| r, _, e1 := syscall.Syscall6(uintptr(unix.SYS_OPEN_TREE), uintptr(0), uintptr(unsafe.Pointer(_p0)), | ||
| uintptr(flags), 0, 0, 0) | ||
| if e1 != 0 { | ||
| err = e1 | ||
| } | ||
| return int(r), nil | ||
| } | ||
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| // moveMount is a wrapper for the the move_mount syscall. | ||
| func moveMount(fdTree int, target string) (err error) { | ||
| var _p0, _p1 *byte | ||
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| empty := "" | ||
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| if _p0, err = syscall.BytePtrFromString(target); err != nil { | ||
| return err | ||
| } | ||
| if _p1, err = syscall.BytePtrFromString(empty); err != nil { | ||
| return err | ||
| } | ||
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| flags := _MOVE_MOUNT_F_EMPTY_PATH | ||
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| _, _, e1 := syscall.Syscall6(uintptr(unix.SYS_MOVE_MOUNT), | ||
| uintptr(fdTree), uintptr(unsafe.Pointer(_p1)), | ||
| 0, uintptr(unsafe.Pointer(_p0)), uintptr(flags), 0) | ||
| if e1 != 0 { | ||
| err = e1 | ||
| } | ||
| return | ||
| } | ||
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| // mountSetAttr is a wrapper for the mount_setattr syscall | ||
| func mountSetAttr(dfd int, path string, flags uint, attr *attr, size uint) (err error) { | ||
| var _p0 *byte | ||
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| if _p0, err = syscall.BytePtrFromString(path); err != nil { | ||
| return err | ||
| } | ||
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| _, _, e1 := syscall.Syscall6(uintptr(unix.SYS_MOUNT_SETATTR), uintptr(dfd), uintptr(unsafe.Pointer(_p0)), | ||
| uintptr(flags), uintptr(unsafe.Pointer(attr)), uintptr(size), 0) | ||
| if e1 != 0 { | ||
| err = e1 | ||
| } | ||
| return | ||
| } | ||
|
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| // createIDMappedMount creates a IDMapped bind mount from SOURCE to TARGET using the user namespace | ||
| // for the PID process. | ||
| func createIDMappedMount(source, target string, pid int) error { | ||
| path := fmt.Sprintf("/proc/%d/ns/user", pid) | ||
| userNsFile, err := os.Open(path) | ||
| if err != nil { | ||
| return errors.Wrapf(err, "unable to get user ns file descriptor for %q", path) | ||
| } | ||
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| var attr attr | ||
| attr.attrSet = _MOUNT_ATTR_IDMAP | ||
| attr.attrClr = 0 | ||
| attr.propagation = 0 | ||
| attr.userNs = uint64(userNsFile.Fd()) | ||
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| defer userNsFile.Close() | ||
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| targetDirFd, err := openTree(source, _OPEN_TREE_CLONE|unix.AT_RECURSIVE) | ||
| if err != nil { | ||
| return err | ||
| } | ||
| defer unix.Close(targetDirFd) | ||
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| if err := mountSetAttr(targetDirFd, "", unix.AT_EMPTY_PATH|unix.AT_RECURSIVE, | ||
| &attr, uint(unsafe.Sizeof(attr))); err != nil { | ||
| return err | ||
| } | ||
| if err := os.Mkdir(target, 0700); err != nil && !os.IsExist(err) { | ||
| return err | ||
| } | ||
| return moveMount(targetDirFd, target) | ||
| } | ||
|
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| // createUsernsProcess forks the current process and creates a user namespace using the specified | ||
| // mappings. It returns the pid of the new process. | ||
| func createUsernsProcess(uidMaps []idtools.IDMap, gidMaps []idtools.IDMap) (int, func(), error) { | ||
| pid, _, err := syscall.Syscall6(uintptr(unix.SYS_CLONE), unix.CLONE_NEWUSER|uintptr(unix.SIGCHLD), 0, 0, 0, 0, 0) | ||
| if err != 0 { | ||
| return -1, nil, err | ||
| } | ||
| if pid == 0 { | ||
| _ = unix.Prctl(unix.PR_SET_PDEATHSIG, uintptr(unix.SIGKILL), 0, 0, 0) | ||
| // just wait for the SIGKILL | ||
| for { | ||
| syscall.Syscall6(uintptr(unix.SYS_PAUSE), 0, 0, 0, 0, 0, 0) | ||
| } | ||
| } | ||
| cleanupFunc := func() { | ||
| unix.Kill(int(pid), unix.SIGKILL) | ||
| _, _ = unix.Wait4(int(pid), nil, 0, nil) | ||
| } | ||
| writeMappings := func(fname string, idmap []idtools.IDMap) error { | ||
| mappings := "" | ||
| for _, m := range idmap { | ||
| mappings = mappings + fmt.Sprintf("%d %d %d\n", m.ContainerID, m.HostID, m.Size) | ||
| } | ||
| return ioutil.WriteFile(fmt.Sprintf("/proc/%d/%s", pid, fname), []byte(mappings), 0600) | ||
| } | ||
| if err := writeMappings("uid_map", uidMaps); err != nil { | ||
| cleanupFunc() | ||
| return -1, nil, err | ||
| } | ||
| if err := writeMappings("gid_map", gidMaps); err != nil { | ||
| cleanupFunc() | ||
| return -1, nil, err | ||
| } | ||
|
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| return int(pid), cleanupFunc, nil | ||
| } |
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