[PATCH] libio: Free backup area when it not required (BZ#22415)

[Adhemerval Zanella]

On 14/12/2017 09:57, Florian Weimer wrote:
> On 11/29/2017 02:39 PM, Adhemerval Zanella wrote:
>> Some libio operations fail to correctly free the backup area (created
>> by_IO_{w}default_pbackfail on unget{w}c) resulting in either invalid
>> buffer free operations or memory leaks.
>>
>> For instance, on the example provided by BZ#22415 a following
>> fputc after a fseek to rewind the stream issues an invalid free on
>> the buffer.
> 
> Do we have to treat this as a security bug?  I don't think so, but I'd still like a second opinion.
> 
> Thanks,
> Florian

I am not well versed in exploit crafting, so how do we usually handle
invalid free on user provided buffers?