[PATCH 2/4] Free the data returned by XGetWindowProperty()

[Alan Coopersmith]

On 05/20/15 05:58 AM, Eirik Byrkjeflot Anonsen wrote:
> Eirik Byrkjeflot Anonsen <eirik at eirikba.org> writes:
>
>> Signed-off-by: Eirik Byrkjeflot Anonsen <eirik at eirikba.org>
>> ---
>>   xprop.c | 7 +++++--
>>   1 file changed, 5 insertions(+), 2 deletions(-)
>>
>> diff --git a/xprop.c b/xprop.c
>> index ba23b87..010eff4 100644
>> --- a/xprop.c
>> +++ b/xprop.c
>> @@ -1442,9 +1442,12 @@ Get_Window_Property_Data_And_Type (Atom atom,
>>       unsigned long nitems;
>>       unsigned long nbytes;
>>       unsigned long bytes_after;
>> -    unsigned char *prop;
>> +    static unsigned char *prop = NULL;
>>       int status;
>> -	
>> +
>> +    if (prop)
>> +	XFree(prop);
>> +
>>       status = XGetWindowProperty(dpy, target_win, atom, 0, (max_len+3)/4,
>>   				False, AnyPropertyType, &actual_type,
>>   				&actual_format, &nitems, &bytes_after,
>
> Though now that I look at this one, I wonder whether I can really trust
> XGetWindowProperty() to always set 'prop', even if it fails. Maybe I
> should add "prop = NULL" after the call to XFree()?

You can't, since we didn't fix Xlib to always set it until just recently:
http://cgit.freedesktop.org/xorg/lib/libX11/commit/src/GetProp.c?id=192bbb9e2fc45df4e17b35b6d14ea0eb418dbd39

In this case, you'd be safe as long as no one removes the Fatal_Error
calls on failure, but because we can't guarantee that will never happen,
I'd be happier with setting it to NULL after the XFree, since that's
cheap and lowest risk.

-- 
	-Alan Coopersmith-              alan.coopersmith at oracle.com
	 Oracle Solaris Engineering - http://blogs.oracle.com/alanc