JEP 411, removal of finalizers, a path forward.
peter.firmstone at zeus.net.au
Sun Aug 1 02:14:34 UTC 2021
So far we have dealt with CORBA (external library), pack200 (working on
an external lib) and to support Java 17, removed some Activation class
dependencies (we don't use RMID, so grabbed the missing Activation
classes from Apache Harmony), thankfully these were not challenging,
although replacement of some Activation classes will require downstream
developers to edit their imports and recompile their code, some are
still stuck on Jini 2.1 api compatibility, I have a Jini 2.1
compatibility layer, that allows them to use JGDMS without re-compiling,
they will be impacted by the changes. There are a number of projects
that use the Jini 2.1 api still.
We have a number of our own permission implementations of course, such
as DeSerialzationPermission and one that's misnamed called
DownloadPermission, which should have been called
"ClassLoadingPermission", because it doesn't prevent code downloads,
URLPermission does that.
These are actually external defenses, and are best granted to
authenticated services (dynamically granted incrementally following
successful authentication), these are gates in the process of loading a
We only let the good guys through the door, but we still have a gun safe
to stop the kids from accidentally shooting each other.
So we've figured out that we can recreate most of the authentication
layer, the challenges will be implementing Java platform level guards.
That's why we still need authorization controls on things like
ClassLoading, network, filesystems and properties, once we allow the
service proxy to load code. It appears unlikely that OpenJDK will
provide hooks here, so we need to wait for finalizers to be removed, so
we can instrument constructors (we don't want to inadvertently open any
holes to the outside by making ClassLoader sensitive to finalizer attacks).
Perhaps with ClassLoader, we should instead guard the actual methods
that load classes instead of the constructor, it's not practical to do
that with network connections however as it would take a big performance
hit, same with filesystems. Our reimplementation of URLClassLoader is
much faster because it doesn't make unnecessary DNS calls, so a small
impact with guards, we may still be faster anyway.
The policy tool currently used for auditing to establish trust will need
to be replaced by new tools that OpenJDK is providing in future.
Clearly auditing needs to increase to offset missing permission checks.
Once we do that, then we can use SHA hashes to identify codebases and
allow their classes to be loaded.
It's still a moving target, with potentially significant implications if
we get it wrong.
Whether we continue developing in Java will depend on a number of factors:
1. How successful we are at navigating JEP 411.
2. Other future JEP disruptors (assuming we succeed with JEP 411).
3. Overall cost of development and maintenance in Java, v's another
4. Cost / benefit of using another language.
5. API stability of other languages.
6. Longevity of other languages v's Java.
I'm working on the assumption that OpenJDK will close any external holes
currently defended by permission checks. It would be good if the JDK
was secure by default, with properties required to be set for allowing
such things as agents, management, parsing xml and serialization.
We still need some authorization layer controls for trusted users and
services, and balance it with increased auditing of code. It's not
possible with static analysis to determine the intended use of
reflection, so we'll need new observability tools to replace the current
policy tools. Perhaps we can link the observability tools to a service
watchdog, if a service proxy misbehaves, then, it gets blacklisted and
the affected JVM is immediately restarted.
Our code is dynamic, so we might need to create an audit service that
provides a list of audited proxy codebases and their SHA-256 hashes.
Keep in mind this is all completely experimental and subject to change.
On 31/07/2021 6:22 pm, Ron Pressler wrote:
> Hi Peter.
> - JEP 411, like every spec-changing JEP, is meant to allow those that use the removed functionality
> a migration path forward. The API elements that are deprecated for removal have some years before
> they are actually removed, so there’s nothing too urgent other than beginning to think of a migration
> path. I think it’s still too soon to consider concrete suggestions for change, especially non-trivial
> - If by Java 8 EOL you mean the time when the last vendor offers extended support for it, then
> 2030 is, I believe, the *earliest* possible date that is guaranteed *now. It’s possible that support
> would be extended until 2130. Such offerings have no bearing on the development of current JDK
> - The number of significant code changes required since JDK 8 to keep up with current JDK releases is,
> for the vast majority of Java users, low (what’s affected most users is reliance on non-spec-compliant
> libraries, and the need to import the external artefacts for EE). The most impactful change has probably
> been the removal of some client deployment technologies from the Oracle JDK, but as far as OpenJDK is
> concerned, the affected areas have been CORBA, pack200, Nashorn, and now the process to remove SM is
> starting. The number of people using any one of these is low, and the number of those who need to work
> hard for alternatives is very low. I think that advance warning, and then support offerings by multiple
> vendors for those who have not managed to migrate in the advance warning period is reasonable; always
> offering ways to support removed technologies together with new features in current releases with the
> same code base is not. When compared with other ecosystems, Java’s strategy is exceptionally tolerant
> of those that prefer slow change.
> - Property-based testing is wonderful, I wish more people would use it, and I hope to see it used in
> the JDK as well. Java has several PBT tools, but I believe the most popular one these days is
> https://jqwik.net/. As long as you’re still with Java, give it a try.
> — Ron
>> On 31 Jul 2021, at 04:04, Peter Firmstone<peter.firmstone at zeus.net.au> wrote:
>> The current JEP 411 plan of action, if left unchanged, will leave developers who adopted the SM architecture as an authorization layer unable to upgrade to later versions of Java, until finalizers and the finalizer attack defensive methods in constructors are removed. JEP 411 has the potential to cause significant disruption for a small proportion of Java developers, but doesn't have to if managed appropriately.
>> The blocker is the ability to implement guard checks using Agents on public API, due to finalizer attack defensive private static methods in constructors.
>> Allan has advised when finalizers are removed, it will be practical to use Agents to instrument public API to implement an authorization layer, this is try, so can it be coordinated with JEP 411 et al?
>> Furthermore, as developers must support multiple Java releases, I propose the following amendments, to ease difficulties of multiple release support (with multi release jars):
>> * AccessController, AccessControlContext, DomainCombiner and related
>> Subject and Executors methods, remain until Java 8 is EOL in 2030.
>> Also consider un-deprecation of these methods, as their removal
>> causes shotgun surgery (used in 1000's of locations in my software
>> alone) and they are required for preservation of Subject, used for
>> obtaining TLS and Kerberos connection credentials on all existing
>> versions of Java.
>> * AccessControlContext - remove inherited thread context, replace it
>> with an unprivileged ProtectionDomain, such that doPrivileged
>> methods are required for authorization checks and only the current
>> thread stack needs to be walked when checks occur, and stack walks
>> aren't unnecessarily performed when creating new threads. This is
>> compatible with Loom, update loom to allow the use of
>> AccessControlContext to be used, to establish TLS and Kerberos
>> connections. Loom will be very useful for network connections,
>> especially long latency connections over the internet, which are
>> typically secured using TLS. This removes the problem of viral
>> checks, and Executor task privilege escalation.
>> * Modules that are mapped to the boot loader should get a unique PD
>> that includes a useful code source rather than using a "shared" PD,
>> this allows us to reduce the privileged footprint of the Java
>> platform libraries, to allow privileges to be granted to users, not
>> code, or users and code. This is useful to limit data parsing
>> privileges to authenticated users on servers (a practise that should
>> be more widely encouraged).
>> * Remove finalizers, and defensive methods in constructors where
>> permissions check points occur as these cause problems for Agents,
>> prior to removal of SecurityManager.
>> * Deprecate for removal Permission implementations, then remove them
>> in a following release.
>> * Remove SecurityManager.
>> This allows a forward migration path for poor sod's like myself who are currently using SM infrastructure as an authorization layer, and to establish TLS conenctions, this or at least some sort of compromise is far preferable to the thermonuclear option currently planned.
>> What I would like OpenJDK to consider, is to allow developers like myself to continue to stay current with Java, by coordinating the removal of finalizers and defensive methods in constructors, with JEP 411, so we have a workable future migration path. Without these considerations, options are; go back to Java 8, and plan to redevelop existing software, if forced to do so, Java is unlikely to be on the list for redevelopment, simply because development costs are lower in newer languages, such as automated unit tests,https://hackage.haskell.org/package/QuickCheck, no need to worry about null pointers and less boilerplate.
>> Don't get me wrong, I like Java and have many years experience with it, but I have to be pragmatic, it won't just be me, many other developers, when Java 8 is EOL, will work for companies stuck on that platform, simply due to the number of changes required, because they haven't kept up (eg budgets) with the current release cadence and pace of development, will be looking at redevelopment and replacement instead of migration. Clearly the current pace of development is a good thing for Java, but the overall strategy could be tweaked a little, to ensure migration doesn't become insurmountable. A healthy and vibrant Java community is essential for the survival of Java, Java has already shed phone and client markets, lets not shed too many more.
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