On Fri, 12 May 2023 15:24:19 GMT, Volker Simonis <[email protected]> wrote:
> Since JDK13, executing commands in a sub-process defaults to the so called
> `POSIX_SPAWN` launching mechanism (i.e.
> `-Djdk.lang.Process.launchMechanism=POSIX_SPAWN`) on Linux. This works by
> using `posix_spawn(3)` to firstly start a tiny helper program called
> `jspawnhelper` in a subprocess. In a second step, `jspawnhelper` reads the
> command data from the parent Java process over a Unix pipe and finally
> executes (i.e. `execvp(3)`) the requested command.
>
> In cases where the parent process terminates abnormally before `jspawnhelper`
> has read all the expected data from the pipe, `jspawnhelper` will block
> indefinitely on the reading end of the pipe. This is especially harmful if
> the parent process had open sockets, because in that case, the forked
> `jspawnhelper` process will inherit them and keep all the corresponding ports
> open effectively preventing other processes to bind to them. Notice that this
> is not an abstract scenario. We've observed this regularly in production with
> services which couldn't be restarted after a crash after migrating to JDK 17.
>
> The fix of the issue is rather trivial. `jspawnhelper` has to close its
> writing end of the pipe which connects it with the parent Java process
> *before* starting to read from that pipe such that reads from the pipe can
> immediately return with EOF if the parent process terminates abnormally.
>
> Also did some cleanup:
> - in `jspawnhelper.c` correctly chek the result of `readFully()`
> - in `ProcessImpl_md.c` use `restartableWrite()` instead of `write()` to
> write the command data from the parent process to `jspawnhelper`
> - in `childproc.{c,h}` remove remaining traces of `MODE_CLONE` because
> that's long gone.
This pull request has now been integrated.
Changeset: 39f6d807
Author: Volker Simonis <[email protected]>
URL:
https://git.openjdk.org/jdk/commit/39f6d807dbbe0c9ecd72fe2f76bfbc3091b43c80
Stats: 389 lines in 5 files changed: 351 ins; 11 del; 27 mod
8307990: jspawnhelper must close its writing side of a pipe before reading from
it
Reviewed-by: stuefe, rriggs
-------------
PR: https://git.openjdk.org/jdk/pull/13956
