| 1 | //go:build unix |
| 2 | |
| 3 | package hostguard |
| 4 | |
| 5 | import ( |
| 6 | "context" |
| 7 | "errors" |
| 8 | "os" |
| 9 | "time" |
| 10 | |
| 11 | "golang.org/x/sys/unix" |
| 12 | ) |
| 13 | |
| 14 | func acquire(ctx context.Context, dir, host string, verifyOwner ...bool) (func(), error) { |
| 15 | if ctx == nil { |
| 16 | return nil, ErrInvalidInput |
| 17 | } |
| 18 | if err := ctx.Err(); err != nil { |
| 19 | return nil, err |
| 20 | } |
| 21 | if err := validateFileHost(host); err != nil { |
| 22 | return nil, err |
| 23 | } |
| 24 | dirFD, err := openDirectory(dir) |
| 25 | if err != nil { |
| 26 | return nil, err |
| 27 | } |
| 28 | defer unix.Close(dirFD) |
| 29 | var parent unix.Stat_t |
| 30 | if err := unix.Fstat(dirFD, &parent); err != nil { |
| 31 | return nil, err |
| 32 | } |
| 33 | unsafe := func(st unix.Stat_t) bool { |
| 34 | return st.Mode&unix.S_IFMT != unix.S_IFREG || (len(verifyOwner) == 1 && verifyOwner[0] && st.Uid != 0 && st.Uid != parent.Uid) |
| 35 | } |
| 36 | var prior unix.Stat_t |
| 37 | if err := unix.Fstatat(dirFD, host+".lock", &prior, unix.AT_SYMLINK_NOFOLLOW); err == nil && unsafe(prior) { |
| 38 | return nil, ErrUnsafeFile |
| 39 | } |
| 40 | flags := unix.O_RDWR | unix.O_CREAT | unix.O_NOFOLLOW | unix.O_CLOEXEC | unix.O_NONBLOCK |
| 41 | fd, err := unix.Openat(dirFD, host+".lock", flags|unix.O_EXCL, 0660) |
| 42 | created := err == nil |
| 43 | if errors.Is(err, unix.EEXIST) { |
| 44 | fd, err = unix.Openat(dirFD, host+".lock", flags, 0660) |
| 45 | } |
| 46 | if err != nil { |
| 47 | if errors.Is(err, unix.ELOOP) || errors.Is(err, unix.EISDIR) { |
| 48 | return nil, ErrUnsafeFile |
| 49 | } |
| 50 | return nil, err |
| 51 | } |
| 52 | f := os.NewFile(uintptr(fd), host+".lock") |
| 53 | fail := func(err error) (func(), error) { f.Close(); return nil, err } |
| 54 | var st unix.Stat_t |
| 55 | if err := unix.Fstat(fd, &st); err != nil { |
| 56 | return fail(err) |
| 57 | } |
| 58 | if unsafe(st) { |
| 59 | return fail(ErrUnsafeFile) |
| 60 | } |
| 61 | if created && len(verifyOwner) == 1 && verifyOwner[0] && os.Geteuid() == 0 { |
| 62 | if err := unix.Fchown(fd, -1, int(parent.Gid)); err != nil { |
| 63 | return fail(err) |
| 64 | } |
| 65 | } |
| 66 | if created || st.Mode&07777 != 0660 { |
| 67 | if err := unix.Fchmod(fd, 0660); err != nil { |
| 68 | return fail(err) |
| 69 | } |
| 70 | } |
| 71 | delay := 10 * time.Millisecond |
| 72 | for { |
| 73 | if err := ctx.Err(); err != nil { |
| 74 | return fail(err) |
| 75 | } |
| 76 | err := unix.Flock(int(f.Fd()), unix.LOCK_EX|unix.LOCK_NB) |
| 77 | if err == nil { |
| 78 | unlock := func() { _ = unix.Flock(int(f.Fd()), unix.LOCK_UN); _ = f.Close() } |
| 79 | if err := ctx.Err(); err != nil { |
| 80 | unlock() |
| 81 | return nil, err |
| 82 | } |
| 83 | return unlock, nil |
| 84 | } |
| 85 | if !errors.Is(err, unix.EWOULDBLOCK) && !errors.Is(err, unix.EAGAIN) && !errors.Is(err, unix.EINTR) { |
| 86 | return fail(err) |
| 87 | } |
| 88 | timer := time.NewTimer(delay) |
| 89 | select { |
| 90 | case <-ctx.Done(): |
| 91 | timer.Stop() |
| 92 | return fail(ctx.Err()) |
| 93 | case <-timer.C: |
| 94 | } |
| 95 | delay = min(2*delay, 100*time.Millisecond) |
| 96 | } |
| 97 | } |
| 98 | |
amadan