RFR: 8349546: Linux support for Kerberos "nativeccache" functionality

[Erik Joelsson]

On Thu, 30 Oct 2025 22:55:34 GMT, Erik Joelsson <erikj at openjdk.org> wrote:

>> _Purpose_
>> 
>> This PR allows Linux based applications using JAAS to acquire Kerberos TGTs natively using the local system's Kerberos libraries/configuration, building on existing support on Windows/MacOSX.
>> 
>> _Rationale_
>> 
>> Currently the (pure java) JAAS codebase only supports file-based credential caches (ccaches).  There are many other useful types of ccache accessible via the local system libraries; this change allows credentials to be acquired natively using those libraries, and thus adds support for all other ccache types supported by the local system (e.g. KCM, in-memory and kernel types),  This support already exists on MacOSX and Windows.
>> 
>> The code change here largely uses the MacOSX code, edited for Linux with associated build system changes. It also adds an appropriate jtreg test which uses some native test helper code to manufacture an in-memory cache, and then uses the new code to acquire these credentials natively.  This has been tested on Linux/Mac and the jtreg test passes on each (I couldn't see any existing tests on MacOSX for this feature).
>> 
>> Additionally this PR fixes a bug that's existed for a while (see L585-588 in `nativeccache.c`) - without this code, this is a 100% reproducible segfault on Linux (it's unclear why this hasn't affected the Mac JVMs up to now, probably just no calling code that provides an empty list of addresses).  It also fixes a (non problem) typo in the variable name in a function prototype.
>> 
>> _Implementation Detail_
>> 
>> Note that there were multiple possible ways of doing this:
>> 
>> 1) Duplicate the MacOSX `nativeccache.c`, edit lightly for Linux and build a new library on Linux only (`liblinuxkrb5`), leaving MacOSX largely unchanged, but at the expense of this code duplication.
>> 
>> 2) Create a new shared library used on both platforms with conditional compilation to manage the differences.  This necessitates a library name change on MacOSX and potentially knock-on packaging changes on that platform, which seemed a potentially expensive side-effect.
>> 
>> 3) Create a shared `nativeccache.c` (using `EXTRA_SRC` in the build) and build separate MacOSX/Linux libraries.  This allows the MacOSX library name to remain unchanged, and only adds a new library in Linux.
>> 
>> I tried all three options; 3 seemed to be the best compromise all around, although is one of the options that effectively introduces a "no-op" change on MacOSX as a result.  Hopefully the additional jtreg test is sufficient to compensat...
>
> Is there a particular reason for build.sh in the tests or are you just not familiar with how native test code gets automatically compiled by the makefiles based on file naming conventions? In short, any file `lib*.c[pp]` will get compiled into a native library (and exe*.c[pp] into an executable). You can define any special flags or platform include/exclude in `make/test/JtregNativeJdk.gmk`.

> Hi @erikj79, I noticed that in our CI build the library is not built and the log shows
> 
> ```
> checking for krb5 (<omitted>)... no
> checking krb5.h usability... no
> checking krb5.h presence... no
> checking for krb5.h... no 
> ```
> 
> How can we require them to be present?

Is this intended to be a required dependency for OpenJDK or are you referring to how we would enable this feature and dependency for Oracle builds?

If the latter, they would need to be part of the devkit that we use. So the first step would be to modify the devkit creation makefiles for Linux in `make/devkit/...`, then create a new devkit, verify and deploy internally.

You will also need to verify that libkrb5 is reasonably stable and compatible across versions, since we only build one JDK distribution per architecture for Linux. We use a sysroot from the oldest Linux distribution we support, so you would need to verify that linking against libkrb5 in that sysroot/devkit results in a JDK that is still runtime compatible with all the Linux versions we support.

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PR Comment: https://git.openjdk.org/jdk/pull/28075#issuecomment-3543727972