| 1 | //go:build linux |
| 2 | |
| 3 | package activator |
| 4 | |
| 5 | import ( |
| 6 | "errors" |
| 7 | "os" |
| 8 | "syscall" |
| 9 | |
| 10 | "golang.org/x/sys/unix" |
| 11 | |
| 12 | "github.com/carlosframework/platform/internal/hostbox" |
| 13 | ) |
| 14 | |
| 15 | // pinRootProcess returns the process root granted at pid, pinned by a pidfd |
| 16 | // that was opened before its start was compared with start. The pin, not the |
| 17 | // pid, is what the watcher follows, so a reused pid can never stand in for |
| 18 | // the grant's process. A pid that is already gone (ESRCH) is the grant's |
| 19 | // process having exited and returns a process that reads as exited. A pidfd |
| 20 | // that cannot be opened for any other reason is an error, never an exit. |
| 21 | func pinRootProcess(pid int, start string) (*os.Process, error) { |
| 22 | process, err := os.FindProcess(pid) |
| 23 | if err != nil { |
| 24 | return nil, err |
| 25 | } |
| 26 | pinned := false |
| 27 | err = process.WithHandle(func(fd uintptr) { |
| 28 | got, e := roleProcessStart(pid) |
| 29 | // The start was read through the pid. It is the pinned process's |
| 30 | // only if that process had not exited by the time it was read. |
| 31 | pinned = e == nil && got == start && !pidfdExited(int(fd)) |
| 32 | }) |
| 33 | switch { |
| 34 | case processGone(process, err): |
| 35 | return process, nil |
| 36 | case err != nil: |
| 37 | _ = process.Release() |
| 38 | return nil, errors.Join(hostbox.ErrChanged, err) |
| 39 | case !pinned: |
| 40 | _ = process.Release() |
| 41 | return nil, hostbox.ErrChanged |
| 42 | } |
| 43 | return process, nil |
| 44 | } |
| 45 | |
| 46 | // processGone reports whether err, from process's WithHandle, means the |
| 47 | // process has exited. A process found after its pid was gone (ESRCH) has no |
| 48 | // handle and answers Signal without a pidfd, so its pid is asked directly. |
| 49 | func processGone(process *os.Process, err error) bool { |
| 50 | if errors.Is(err, os.ErrNoHandle) { |
| 51 | err = process.Signal(syscall.Signal(0)) |
| 52 | } |
| 53 | return errors.Is(err, os.ErrProcessDone) |
| 54 | } |
| 55 | |
| 56 | // pidfdExited reports whether the process behind fd has exited, without |
| 57 | // waiting. |
| 58 | func pidfdExited(fd int) bool { |
| 59 | fds := []unix.PollFd{{Fd: int32(fd), Events: unix.POLLIN}} |
| 60 | for { |
| 61 | n, err := unix.Poll(fds, 0) |
| 62 | if errors.Is(err, unix.EINTR) { |
| 63 | continue |
| 64 | } |
| 65 | return err != nil || n > 0 |
| 66 | } |
| 67 | } |
| 68 | |
| 69 | // watchRootProcess closes done when process exits. The agent is not the |
| 70 | // process's parent, so it polls the pidfd process was pinned by rather than |
| 71 | // waiting. A process with no pinned pidfd cannot be watched, and done then |
| 72 | // stays open: an unwatchable process is never reported as exited. |
| 73 | func watchRootProcess(process *os.Process, done chan struct{}) { |
| 74 | go func() { |
| 75 | exited := false |
| 76 | err := process.WithHandle(func(fd uintptr) { |
| 77 | fds := []unix.PollFd{{Fd: int32(fd), Events: unix.POLLIN}} |
| 78 | for { |
| 79 | n, err := unix.Poll(fds, -1) |
| 80 | if errors.Is(err, unix.EINTR) { |
| 81 | continue |
| 82 | } |
| 83 | exited = err == nil && n > 0 |
| 84 | return |
| 85 | } |
| 86 | }) |
| 87 | if exited || processGone(process, err) { |
| 88 | close(done) |
| 89 | } |
| 90 | }() |
| 91 | } |
| 92 | |
amadan