| 1 | //go:build unix |
| 2 | |
| 3 | package hostfiles |
| 4 | |
| 5 | import ( |
| 6 | "errors" |
| 7 | "io" |
| 8 | "os" |
| 9 | "sort" |
| 10 | "strconv" |
| 11 | "strings" |
| 12 | |
| 13 | "golang.org/x/sys/unix" |
| 14 | ) |
| 15 | |
| 16 | // restoreDirFlags is how Restore opens a directory it is about to sync: |
| 17 | // read-only, a directory only, never through a link at the last |
| 18 | // component, and never waiting on a FIFO. |
| 19 | const restoreDirFlags = unix.O_RDONLY | unix.O_DIRECTORY | unix.O_NONBLOCK | unix.O_NOFOLLOW |
| 20 | |
| 21 | // dirHandle is a directory held open by descriptor. Everything beneath it |
| 22 | // is reached one path component at a time with openat and O_NOFOLLOW, so |
| 23 | // no symlink is ever followed, inside the tree or out of it, and a |
| 24 | // directory swapped for something else after it was looked at is refused |
| 25 | // rather than entered. Every open is non-blocking, so a FIFO swapped in |
| 26 | // for a file or a directory cannot hang the publisher. |
| 27 | type dirHandle struct{ f *os.File } |
| 28 | |
| 29 | // openTree opens the root of a files directory. The path to the root is |
| 30 | // the platform's own and may contain symlinks; nothing beneath it may. |
| 31 | func openTree(path string) (*dirHandle, error) { |
| 32 | fd, err := unix.Open(path, unix.O_RDONLY|unix.O_DIRECTORY|unix.O_CLOEXEC|unix.O_NONBLOCK, 0) |
| 33 | if err != nil { |
| 34 | return nil, &os.PathError{Op: "open", Path: path, Err: err} |
| 35 | } |
| 36 | return &dirHandle{os.NewFile(uintptr(fd), path)}, nil |
| 37 | } |
| 38 | |
| 39 | // handleOf wraps a directory the caller opened, and keeps, as the root of |
| 40 | // a walk: SyncDirAt never closes it. Anything but a directory is refused. |
| 41 | func handleOf(f *os.File) (*dirHandle, error) { |
| 42 | if f == nil { |
| 43 | return nil, errors.New("hostfiles: sync of a nil directory") |
| 44 | } |
| 45 | info, err := f.Stat() |
| 46 | if err != nil { |
| 47 | return nil, err |
| 48 | } |
| 49 | if !info.IsDir() { |
| 50 | return nil, &os.PathError{Op: "sync", Path: f.Name(), Err: unix.ENOTDIR} |
| 51 | } |
| 52 | return &dirHandle{f}, nil |
| 53 | } |
| 54 | |
| 55 | func (d *dirHandle) Close() error { return d.f.Close() } |
| 56 | func (d *dirHandle) Name() string { return d.f.Name() } |
| 57 | |
| 58 | // openDir opens the directory name inside d. A name that is not a real |
| 59 | // directory (a symlink, a file, a FIFO) fails with ENOTDIR or ELOOP |
| 60 | // without blocking; a missing one with ENOENT. |
| 61 | func (d *dirHandle) openDir(name string) (*dirHandle, error) { |
| 62 | fd, err := unix.Openat(int(d.f.Fd()), name, unix.O_RDONLY|unix.O_DIRECTORY|unix.O_NOFOLLOW|unix.O_CLOEXEC|unix.O_NONBLOCK, 0) |
| 63 | if err != nil { |
| 64 | return nil, &os.PathError{Op: "openat", Path: name, Err: err} |
| 65 | } |
| 66 | return &dirHandle{os.NewFile(uintptr(fd), name)}, nil |
| 67 | } |
| 68 | |
| 69 | // names lists d's entries, sorted. |
| 70 | func (d *dirHandle) names() ([]string, error) { |
| 71 | if _, err := d.f.Seek(0, io.SeekStart); err != nil { |
| 72 | return nil, err |
| 73 | } |
| 74 | names, err := d.f.Readdirnames(-1) |
| 75 | if err != nil { |
| 76 | return nil, err |
| 77 | } |
| 78 | sort.Strings(names) |
| 79 | return names, nil |
| 80 | } |
| 81 | |
| 82 | // look inspects name inside d without following a symlink. |
| 83 | func (d *dirHandle) look(name string) (unix.Stat_t, error) { |
| 84 | var st unix.Stat_t |
| 85 | err := unix.Fstatat(int(d.f.Fd()), name, &st, unix.AT_SYMLINK_NOFOLLOW) |
| 86 | return st, err |
| 87 | } |
| 88 | |
| 89 | func isDir(st unix.Stat_t) bool { return st.Mode&unix.S_IFMT == unix.S_IFDIR } |
| 90 | func isRegular(st unix.Stat_t) bool { return st.Mode&unix.S_IFMT == unix.S_IFREG } |
| 91 | |
| 92 | func sameFile(a, b unix.Stat_t) bool { return a.Dev == b.Dev && a.Ino == b.Ino } |
| 93 | |
| 94 | func sameImage(a, b unix.Stat_t) bool { |
| 95 | return sameFile(a, b) && a.Size == b.Size && a.Mtim == b.Mtim |
| 96 | } |
| 97 | |
| 98 | // notADirectory reports the errors openDir gives for a name that exists |
| 99 | // but is not a real directory. |
| 100 | func notADirectory(err error) bool { |
| 101 | return errors.Is(err, unix.ENOTDIR) || errors.Is(err, unix.ELOOP) |
| 102 | } |
| 103 | |
| 104 | // descend opens the directory rel ("" or "a/b") beneath d, one component |
| 105 | // at a time. gone is true when some component is missing or is not a real |
| 106 | // directory: nothing of ours lives at a path under it. |
| 107 | // |
| 108 | // A component that is "", "." or ".." is refused with an error, never |
| 109 | // reported as gone: publishOne relies on descend never leaving the tree. |
| 110 | // descend("") returns d itself, so the caller must not close it. |
| 111 | func (d *dirHandle) descend(rel string) (sub *dirHandle, gone bool, err error) { |
| 112 | if rel == "" { |
| 113 | return d, false, nil |
| 114 | } |
| 115 | parts := strings.Split(rel, "/") |
| 116 | for _, part := range parts { |
| 117 | if part == "" || part == "." || part == ".." { |
| 118 | return nil, false, errors.New("hostfiles: path component " + strconv.Quote(part) + " in " + strconv.Quote(rel) + " is not a plain name") |
| 119 | } |
| 120 | } |
| 121 | cur, owned := d, false |
| 122 | for _, part := range parts { |
| 123 | betweenLookAndOpen() |
| 124 | next, err := cur.openDir(part) |
| 125 | if owned { |
| 126 | cur.Close() |
| 127 | } |
| 128 | if err != nil { |
| 129 | if errors.Is(err, unix.ENOENT) || notADirectory(err) { |
| 130 | return nil, true, nil |
| 131 | } |
| 132 | return nil, false, err |
| 133 | } |
| 134 | cur, owned = next, true |
| 135 | } |
| 136 | return cur, false, nil |
| 137 | } |
| 138 | |
| 139 | // readStable reads the file name inside d for publishing. |
| 140 | // |
| 141 | // It reads only what it opened without following a link and found to be |
| 142 | // the same regular file it had just inspected. A file over MaxFileBytes is |
| 143 | // refused on its size alone, before any read. What it reports: |
| 144 | // |
| 145 | // - fileGone: nothing by that name. |
| 146 | // - fileNotRegular: something by that name that is not a regular file. |
| 147 | // - fileUnreadable: a regular file that could not be opened or read. It |
| 148 | // still exists, so the caller must keep what the manifest has for it. |
| 149 | // - fileRetry: the regular file was replaced by another regular file |
| 150 | // between the look and the open. Nothing was read; ask again. |
| 151 | // - fileTorn: read, but its size, mtime or identity changed meanwhile. |
| 152 | // The bytes are a possibly inconsistent image. |
| 153 | func readStable(d *dirHandle, name string) ([]byte, uint32, fileState, error) { |
| 154 | before, err := d.look(name) |
| 155 | if errors.Is(err, unix.ENOENT) { |
| 156 | return nil, 0, fileGone, nil |
| 157 | } |
| 158 | if err != nil { |
| 159 | return nil, 0, fileUnreadable, nil |
| 160 | } |
| 161 | if !isRegular(before) { |
| 162 | return nil, 0, fileNotRegular, nil |
| 163 | } |
| 164 | if before.Size > MaxFileBytes { |
| 165 | return nil, 0, fileTooLarge, nil |
| 166 | } |
| 167 | betweenLookAndOpen() |
| 168 | fd, err := unix.Openat(int(d.f.Fd()), name, unix.O_RDONLY|unix.O_NOFOLLOW|unix.O_CLOEXEC|unix.O_NONBLOCK, 0) |
| 169 | switch { |
| 170 | case errors.Is(err, unix.ENOENT): |
| 171 | return nil, 0, fileGone, nil |
| 172 | case errors.Is(err, unix.ELOOP): |
| 173 | return nil, 0, fileNotRegular, nil // it became a symlink |
| 174 | case err != nil: |
| 175 | return nil, 0, fileUnreadable, nil |
| 176 | } |
| 177 | f := os.NewFile(uintptr(fd), name) |
| 178 | defer f.Close() |
| 179 | var opened unix.Stat_t |
| 180 | if err := unix.Fstat(fd, &opened); err != nil { |
| 181 | return nil, 0, fileUnreadable, nil |
| 182 | } |
| 183 | if !isRegular(opened) { |
| 184 | return nil, 0, fileNotRegular, nil // swapped for a FIFO, a device, a directory |
| 185 | } |
| 186 | if !sameFile(before, opened) { |
| 187 | return nil, 0, fileRetry, nil |
| 188 | } |
| 189 | if opened.Size > MaxFileBytes { |
| 190 | return nil, 0, fileTooLarge, nil |
| 191 | } |
| 192 | body, err := readAll(io.LimitReader(f, MaxFileBytes+1)) |
| 193 | if err != nil { |
| 194 | return nil, 0, fileUnreadable, nil |
| 195 | } |
| 196 | if int64(len(body)) > MaxFileBytes { |
| 197 | return nil, 0, fileTooLarge, nil // it grew past the cap while being read |
| 198 | } |
| 199 | state := fileOK |
| 200 | if after, err := d.look(name); err != nil || !sameImage(before, after) { |
| 201 | state = fileTorn |
| 202 | } |
| 203 | return body, uint32(before.Mode & 0o777), state, nil |
| 204 | } |
| 205 | |
amadan