[patch] Fix for heap overflow in wscanf (BZ 16618)

[Carlos O'Donell]

On 02/03/2015 07:27 PM, Rich Felker wrote:
> On Tue, Feb 03, 2015 at 04:11:56PM -0800, Paul Eggert wrote:
>> Carlos O'Donell wrote:
>>> I'd read the POSIX wording differently.
>>
>> Although Rich's interpretation is correct for current POSIX, thanks
>> to Eric Blake the next release of POSIX (Issue 8) is planned to
>> change this, and to require 'free' to leave errno alone, which as I
>> understand it is your preferred interpretation.  Please see:
>>
>> http://austingroupbugs.net/view.php?id=385
>>
>> Because of this, glibc 'free' should not set errno if the user
>> invokes 'free' in a conforming way.  Setting errno will be a
>> conformance bug once Issue 8 comes out, and glibc should be fixed to
>> conform well before that.  Also, the glibc documentation should be
>> changed to discuss this issue.  I have filed a glibc bug report to
>> that effect, here:
>>
>> https://sourceware.org/bugzilla/show_bug.cgi?id=17924
> 
> Interesting. Unfortunately this makes it impossible for the
> application to observe the "valid memory was unable to be freed"
> condition that occurs when you can't split a vma. Formally, the memory
> is still freed anyway, so it hardly matters, but it indicates a
> critical situation where things are about to blow up for the
> application (malloc no longer working, etc.) so conceivably an
> application could want to detect and respond to the condition.

Could you expand a bit on the split vma issue? I'm not familiar
with that failure mode.

Cheers,
Carlos.