RFR: JDK-8149461: jmap kills process if non-java pid is specified in the command line

[Thomas Stüfe]

On Fri, Feb 15, 2019 at 3:26 AM David Holmes <david.holmes at oracle.com>
wrote:

> Gary,
>
> What is the overhead of doing the validation? How do we list VMs? Do we
> need to examine every running process to get the list of VMs? Wouldn't
> it be better to check the given process is a VM rather than checking all
> potential VM processes?
>
>
I think this is a valid point. Listing VMs is normally quick (just use jcmd
without any parms) but I have seen this fail or hang rarely in situations
where I then still was able to talk to my VM via pid. I never investigated
this but I would not like to be unable to connect to my VM just because
some rogue VM mailfunctions.

This would be an argument for the alternative I offered in my first answer
- just use the proc file system or a similar mechanism to check only the
pid you plan on sending sigquit to...


> I think there is an onus of responsibility on the user to provide a
> correct pid here, rather than trying to make this foolproof.
>
>
Oh but it can happen quite easily. For example, by pulling up an older jcmd
from your shell history and forgetting to modify the pid. Thank god for the
command name argument option on jcmd, which I now use mostly.

We also had a customer which tried to find all VMs on his machine by
attempting to attach with jcmd to every process, killing them left and
right :)

... Thomas


> Thanks,
> David
>
> On 15/02/2019 5:12 am, Gary Adams wrote:
> > The following commands present a similar kill process behavior:
> >     jcmd
> >     jinfo
> >     jmap
> >     jstack
> >
> > The following commands do not attach.
> >     jstat sun.jvmstat.monitor.MonitorException "not found"
> >     jps no pid arguments
> >
> > This update moves the checkJavaPid method into the
> > common/ProcessArgumentsMatcher.java
> > and applies the check before the pid is used for an attach operation.
> >
> >    Revised webrev: http://cr.openjdk.java.net/~gadams/8149461/webrev.01/
> >
> > On 2/14/19, 12:07 PM, Chris Plummer wrote:
> >> Hi Gary,
> >>
> >> What about the other tools that attach to a user specified process. Do
> >> they also have this issue?
> >>
> >> thanks,
> >>
> >> Chris
> >>
> >> On 2/14/19 8:35 AM, Gary Adams wrote:
> >>> There is an old reported problem that using jmap on a process that is
> >>> not running
> >>> Java could cause the process to terminate. This is due to the SIGQUIT
> >>> used
> >>> when attaching to the process.
> >>>
> >>> It is a fairly simple operation to validate that the pid matches one
> >>> of the known
> >>> running Java processes using VirtualMachine.list().
> >>>
> >>>   Issue: https://bugs.openjdk.java.net/browse/JDK-8149461
> >>>
> >>> Proposed fix:
> >>>
> >>> diff --git a/src/jdk.jcmd/share/classes/sun/tools/jmap/JMap.java
> >>> b/src/jdk.jcmd/share/classes/sun/tools/jmap/JMap.java
> >>> --- a/src/jdk.jcmd/share/classes/sun/tools/jmap/JMap.java
> >>> +++ b/src/jdk.jcmd/share/classes/sun/tools/jmap/JMap.java
> >>> @@ -1,5 +1,5 @@
> >>>  /*
> >>> - * Copyright (c) 2005, 2018, Oracle and/or its affiliates. All
> >>> rights reserved.
> >>> + * Copyright (c) 2005, 2019, Oracle and/or its affiliates. All
> >>> rights reserved.
> >>>   * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
> >>>   *
> >>>   * This code is free software; you can redistribute it and/or modify
> it
> >>> @@ -30,6 +30,7 @@
> >>>  import java.io.InputStream;
> >>>  import java.io.UnsupportedEncodingException;
> >>>  import java.util.Collection;
> >>> +import java.util.List;
> >>>
> >>>  import com.sun.tools.attach.VirtualMachine;
> >>>  import com.sun.tools.attach.VirtualMachineDescriptor;
> >>> @@ -125,6 +126,10 @@
> >>>      private static void executeCommandForPid(String pid, String
> >>> command, Object ... args)
> >>>          throws AttachNotSupportedException, IOException,
> >>>                 UnsupportedEncodingException {
> >>> +        // Before attaching, confirm that pid is a known Java process
> >>> +        if (!checkJavaPid(pid)) {
> >>> +            throw new AttachNotSupportedException();
> >>> +        }
> >>>          VirtualMachine vm = VirtualMachine.attach(pid);
> >>>
> >>>          // Cast to HotSpotVirtualMachine as this is an
> >>> @@ -196,6 +201,19 @@
> >>>          executeCommandForPid(pid, "dumpheap", filename, liveopt);
> >>>      }
> >>>
> >>> +    // Check that pid matches a known running Java process
> >>> +    static boolean checkJavaPid(String pid) {
> >>> +        List<VirtualMachineDescriptor> l = VirtualMachine.list();
> >>> +        boolean found = false;
> >>> +        for (VirtualMachineDescriptor vmd: l) {
> >>> +            if (vmd.id().equals(pid)) {
> >>> +                found = true;
> >>> +                break;
> >>> +            }
> >>> +        }
> >>> +        return found;
> >>> +    }
> >>> +
> >>>      private static void checkForUnsupportedOptions(String[] args) {
> >>>          // Check arguments for -F, -m, and non-numeric value
> >>>          // and warn the user that SA is not supported anymore
> >>
> >>
> >
>
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