[cairo] Crash in cairo_surface_get_mime_data()

Andrea Canciani ranma42 at gmail.com
Tue Oct 4 09:33:38 PDT 2011

On Tue, Oct 4, 2011 at 6:11 AM, Uli Schlachter <psychon at znc.in> wrote:
> On 04.10.2011 11:56, Chris Wilson wrote:
>> On Mon, 03 Oct 2011 23:09:42 +0200, Uli Schlachter <psychon at znc.in> wrote:
>> Non-text part: multipart/mixed
>>> Hi,
>>> attached is a test case which crashes on every cairo version since 1.10. First
>>> it sets some mime data, then it removes that mime data again. The next
>>> cairo_surface_get_mime_data() then dereferences a NULL pointer.
>>> Also attached is a patch which fixes the issue for me.
>>> I wonder if this really is a cairo bug or if I'm just using the API in a wrong
>>> way. Could someone enlighten me?
>> It's a bug. Should have realised when the docs said remove, it meant hide.
>>  ;-)
>> Yours is a nice simple fix, though I wonder if we should fix
>> _cairo_user_data_array_set_data(key, NULL) to actually remove the slot.
> I think that could avoid a memory allocation later on. On the other hand. The
> mime-data array is reinitialized all the time and removing and re-adding mime
> data to a surface doesn't really make sense....
>>> Then I also wonder how this should be added to the test suite. The only thing
>>> that currently calls cairo_surface_get_mime_data() is api-special-cases, but
>>> this problem doesn't really fit into that test. Should this get its own test
>>> case, looking something like the code below?
>> Sure, start a suite of tests for mime-surface-api.c As we also want to make
>> sure that we do get the exact same data returned from get as for set.
>> (The drawing test should cover that, but doesn't actually imply no copy
>> was made etc.)
> Attached are two patches. First one adds a new test case and the other is the
> one-line fix I posted earlier.
> If no one complains, I'll eventually push this.

Should we add a "replace" in the test case?
IIRC it should not matter, because create-replace-destroy should be
the same as create-(destroy-create)-destroy, but... who knows when we
will forget about it and break it in an unnoticed way


> Cheers,
> Uli
> --
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