On Wed, 17 May 2023 12:33:48 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.
>
> Volker Simonis has updated the pull request incrementally with one additional
> commit since the last revision:
>
> Added test case
src/java.base/unix/native/libjava/childproc.c line 408:
> 406: * or the newly created jspawnhelper child process during the execution
> of
> 407: * Java_java_lang_ProcessImpl_forkAndExec().
> 408: * See: test/jdk/java/lang/ProcessBuilder/JspawnhelperProtocol.java
Is there a file missing from the commit? Where is JspawnhelperProtocol.java?
It might be useful to include the bug number; though generally they can get
stale and uninteresting quickly.
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PR Review Comment: https://git.openjdk.org/jdk/pull/13956#discussion_r1196651832
