Emplace vs closures

[John Colvin via Digitalmars-d]

On Tuesday, 20 September 2016 at 08:08:16 UTC, cym13 wrote:
> On Monday, 19 September 2016 at 14:22:16 UTC, Steven 
> Schveighoffer wrote:
>> On 9/19/16 7:27 AM, Lodovico Giaretta wrote:
>>
>>> What I'd like to know: is this usage widespread? Should we 
>>> forbid it for
>>> the sake of security?
>>
>> No. There is no security concern here. You are dereferencing a 
>> null pointer, which is perfectly safe.
>>
>> -Steve
>
> I beg to defer,

You mean differ, right?

> null pointer dereference is certainly not safe in the general 
> case. In many cases it lead to code execution or privilege 
> escalation. See for example CVE-2008-568 [1] for an example in 
> kernel space or CVE-2009-0385 [2] in user space.
>
> The idea is that you are really trying to call a function in a 
> part of memory that is not mapped, but if you are able to map 
> the zero page and control what function pointer is present 
> there then it is exploitable. I'd like people to get away from 
> the idea that null pointer dereference is safe, it's not. In 
> most cases it's not exploitable but that's definitely not a 
> safe spot.
>
> That being said I don't think it should be the burden of the 
> library or language to deal with this for the reasons you 
> exposed.
>
> [1] http://www.trapkit.de/advisories/TKADV2008-015.txt
> [2] http://www.trapkit.de/advisories/TKADV2009-004.txt

Interesting, hadn't seen this stuff before. There is also the 
matter of large offsets taking you to accessible memory, such as 
you might get with a null pointer to a very large struct.