We use the same approach like Elasticsearch (walk through stack trace and check
caller).
Note that this does not work in any case. For example this will bypass
checkExit,
sure, in Java 9 this would also need --add-opens to make reflection work:
Method halt0 =
Class.forName("java.lang.Shutdown").getDeclaredMethod("halt0", int.class);
halt0.setAccessible(true);
halt0.invoke(halt0, 0);
But we can life with that because in our case we just want to find erroneous
code.
It is impossible to protect a JVM from malicious code (which is executed within
the JVM) anyway.
Regards
Reto
Von: Uwe Schindler <[email protected]>
An: 'Alan Bateman' <[email protected]>, 'Reto Merz'
<[email protected]>
Kopie: <[email protected]>
Gesendet: 06.04.2017 16:25
Betreff: RE: SecurityManager environments
Hi,
> > >> To be honest, we don't see a lot of security manager
> > >> usage on the server side these days.
> >
> > I'm really surprised about that. How can a app server or servlet container
> > like JBoss Tomcat etc guarantee that System.exit does not shut down
> > the JVM?
> AFAIK the app servers have to provide a way to run with a security
> manager but I don't know how many app server run it by default.
>
> The System.exit example is a good example that has come up a few times.
> There is at least one IDE that used to run with a SM so that it could
> block plugins from calling System.exit. That use case is one that
> probably needs a specific API.
Elasticsearch Server also blocks System.exit, so plugins or scripts running
inside the query cannot shut down the server (it also blocks many other stuff
for sandboxing everything). The main problem with implementing the exitVM
permission is to make it work that you can still exit on your own 😊 If you
forbid exiting the VM, you cannot do it on your own. (cannot be done in a
policy file, because the exit permission is given by default).
This is by the way a good use case for the new StackWalker API!: The
Elasticsearch (and Apache Lucene's Test Runner) SecurityManager do
Thread.currentThread().getStackTrace() and then walk down the stack and only
allow exiting if the right class/package is on the stack trace right before the
System/Runtime.exit() call. E.g.,
<https://github.com/elastic/securesm/blob/master/src/main/java/org/elasticsearch/SecureSM.java#L199-L249>
<https://github.com/elastic/elasticsearch/blob/master/core/src/main/java/org/elasticsearch/bootstrap/Security.java#L119>
I agree some improvements to SecurityManager around that would be good. It is
really hard to implement that (only allow existing from a specific
class/method), as you need to inspect stack, otherwise you cannot exit on your
own... The code here is still known as "Uwe Schindler" algorithm in the
community, originating from Apache Lucene and was just forked in Elasticsearch.
They made a Maven package out of it (SecureSM is taking a list of packages that
are allowed to exit the VM):
<http://search.maven.org/#search%7Cgav%7C1%7Cg%3A%22org.elasticsearch%22%20AND%20a%3A%22securesm%22>
Uwe
