Budgets ... again

John Ralls jralls at ceridwen.us
Sun Oct 16 19:31:32 EDT 2011

On Sep 26, 2011, at 11:35 AM, Christian Stimming wrote:

> Am Montag, 26. September 2011 schrieb John Ralls:
>> I have a plan to rework the engine (the module which does all of
>> the accounting and business calculations) in stages. Stage one is to write
>> comprehensive tests for each class. Stage two (which will interleave with
>> stage one) is to overhaul each class to be a well-behaved GObject class
>> with all access to data (including KVP) via function calls instead of
>> passing out pointers for other objects to modify at will.
> Out of curiosity: Which examples for "passing out pointers" do you have in 
> mind here? Surely there is plenty of access to KVP data by simply accessing 
> the KVP directly, which is bad, but is there also direct pointer manipulation 
> in that many places?

Here's an example I found today, while investigating bug 661903:
xaccTransGetSplitList() returns a GList* of the splits. The requestor can manipulate or delete the splits, unbalancing or even eviscerating the transaction without the transaction knowing. It's called in 23 places in C and 19 in Scheme.

It doesn't help that Accounts also keep a list of splits and since we're not using GObject reference counting, there's no way to protect against one or both from having invalid pointers. 

The backtrace accompanying the bug shows an attempt to access address 00000000aaaaaaaa -- which is what glib writes into freed memory. I don't know what actually freed the split (given the description of what leads to the crash it doesn't make sense that a freed split should even be encountered), but it probably wasn't the Transaction::do_delete, the only place in Transaction.c that calls xaccSplitDestroy().

John Ralls

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