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From "Bailey, Aaron" <Aaron.Bai...@ga.com>
Subject RE: --EXTERNAL--Re: Bug Report Againgst Subversion 1.9.3 libsvn_subr
Date Thu, 14 Jul 2016 16:56:21 GMT
Hey Stefan,

I think I know what is going on, this is due to my lack of knowledge about the inner workings
of Apache. I'm building subversion for an several older versions of Linux. I couldn't update
the packages on several of them so I statically linked in all of the dependencies for subversion.
So Apache, APR, APR-Util, etc... are still the older system packages while Subversion has
statically built in updated versions. This is not normally an issue for developers as they
aren't running Subversion servers, let alone through Apache. When upgrading the actual server
it was decided not to touch Apache. So if Apache initializes the APR module it would be the
one dynamically linked against the system default shared object APR library, which my build
of subversion doesn't use. ¯\_(ツ)_/¯

I know this is the subversion and not the APR list, but I feel that the APR library segfaulting
if it hasn't been properly initialized is still not great behavior. It may be worth updating
the APR module memory/unix/apr_pools.c to have some of the functions check if APR has been
initialized and return the appropriate apr_status_t. Any thoughts on if it's worth the time
to submit something to their group?

Thank you for taking the time to respond,

Aaron

-----Original Message-----
From: Stefan Sperling [mailto:stsp@elego.de] 
Sent: Thursday, July 14, 2016 1:07 AM
To: Bailey, Aaron
Cc: users@subversion.apache.org
Subject: --EXTERNAL--Re: Bug Report Againgst Subversion 1.9.3 libsvn_subr

On Wed, Jul 13, 2016 at 05:37:36PM +0000, Bailey, Aaron wrote:
> This is an update to the reported issue below.
> 
> It appears that calling the pre-processor macro svn_pool_create with an argument of NULL
is done a lot in the Subversion code base. The comments in the APR function apr_pool_create_ex
 in module memory/unix/apr_pools.c seems to imply you shouldn't do this. However, as long
as you've made a call to either the APR function apr_pool_initialize in the module memory/unix/apr_pools.c
or apr_initialize in one of the OS appropriate APR modules then you're ok as it initializes
the global pool which is used when the parent argument is NULL. However, the stack flow listed
below from the mod_dav_svn subversion module never makes a call to any of the initialization
functions. Ensuring that the APR module has been correctly initialized resolves this issue.
That being said the APR code should probably handle being called before initialization gracefully
rather than just causing a segmentation fault.
> 
> I will note that while I didn't test it, the same issue appears to be present in the
Subversion 1.8.16 code base via code inspection. Since Subversion 1.8, and probably 1.9, are
widely in use maybe something about how I configure / build the code is causing this issue.
That being said, I cannot get the Subversion Apache module to work correctly without first
patching the code to explicitly initialize the APR module (and patching APR to check if it's
been initialized and return an appropriate apr_status_t for good measure).
> 
> Thanks,
> 
> Aaron
> 

It seems odd that you'd be the only person on the planet running into this.
It's such a fundamental problem. Nothing will work if pools don't work.

Shouldn't Apache HTTPD be intializing the process-global APR state?
Perhaps, somehow, there's a problem with the HTTPD that's loading mod_dav_svn?

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