| 1 | //go:build unix |
| 2 | |
| 3 | package host |
| 4 | |
| 5 | import ( |
| 6 | "errors" |
| 7 | "fmt" |
| 8 | "os" |
| 9 | "path/filepath" |
| 10 | "strings" |
| 11 | |
| 12 | "golang.org/x/sys/unix" |
| 13 | "syscall" |
| 14 | ) |
| 15 | |
| 16 | // errRegistryFileShape refuses a registry path that is not a plain, |
| 17 | // single-link regular file. /data belongs to the service user, so anything |
| 18 | // there may have been planted: a symlink or a hard link to a root-owned file |
| 19 | // would otherwise hand that file to the service user when root chowns it. |
| 20 | var errRegistryFileShape = errors.New("not a plain single-link regular file") |
| 21 | |
| 22 | // ownRegistryFile gives path to uid:gid without following a symlink and |
| 23 | // without touching any file reachable by another name. It opens the path |
| 24 | // O_NOFOLLOW, checks the opened file itself, and changes ownership through |
| 25 | // that descriptor, so a swap between the check and the chown cannot redirect |
| 26 | // it. A missing file reports os.ErrNotExist; changed is false when the file |
| 27 | // was already owned as wanted. |
| 28 | func ownRegistryFile(path string, uid, gid int) (changed bool, err error) { |
| 29 | parent, name, err := openRegistryParent(path) |
| 30 | if err != nil { |
| 31 | return false, err |
| 32 | } |
| 33 | defer parent.Close() |
| 34 | fd, err := openRegistryDescriptor(int(parent.Fd()), name) |
| 35 | var f *os.File |
| 36 | if err == nil { |
| 37 | f = os.NewFile(uintptr(fd), path) |
| 38 | } |
| 39 | if err != nil { |
| 40 | if errors.Is(err, syscall.ELOOP) { |
| 41 | return false, fmt.Errorf("%s: %w", path, errRegistryFileShape) |
| 42 | } |
| 43 | return false, err |
| 44 | } |
| 45 | defer f.Close() |
| 46 | fi, err := f.Stat() |
| 47 | if err != nil { |
| 48 | return false, err |
| 49 | } |
| 50 | st, ok := fi.Sys().(*syscall.Stat_t) |
| 51 | if !ok || !fi.Mode().IsRegular() || st.Nlink != 1 { |
| 52 | return false, fmt.Errorf("%s: %w", path, errRegistryFileShape) |
| 53 | } |
| 54 | if int(st.Uid) == uid && int(st.Gid) == gid { |
| 55 | return false, nil |
| 56 | } |
| 57 | if err := chownRegistryDescriptor(f, uid, gid); err != nil { |
| 58 | return false, err |
| 59 | } |
| 60 | return true, nil |
| 61 | } |
| 62 | |
| 63 | // Walk each parent without following symlinks, keeping the final directory pinned. |
| 64 | func openRegistryParent(path string) (*os.File, string, error) { |
| 65 | absolute, err := filepath.Abs(path) |
| 66 | if err != nil { |
| 67 | return nil, "", err |
| 68 | } |
| 69 | parent, err := os.Open("/") |
| 70 | if err != nil { |
| 71 | return nil, "", err |
| 72 | } |
| 73 | for _, part := range strings.Split(strings.TrimPrefix(filepath.Dir(absolute), "/"), "/") { |
| 74 | if part == "" { |
| 75 | continue |
| 76 | } |
| 77 | fd, err := unix.Openat(int(parent.Fd()), part, unix.O_RDONLY|unix.O_DIRECTORY|unix.O_NOFOLLOW|unix.O_CLOEXEC, 0) |
| 78 | parent.Close() |
| 79 | if err != nil { |
| 80 | return nil, "", err |
| 81 | } |
| 82 | parent = os.NewFile(uintptr(fd), part) |
| 83 | } |
| 84 | return parent, filepath.Base(absolute), nil |
| 85 | } |
| 86 | |
amadan