alloca avoidance patches

[Florian Weimer]

On 06/19/2017 10:11 PM, Carlos O'Donell wrote:

> The safety of our users and protecting them against exploits is
> paramount in my opinion, and we should adopt such limits for SUID
> binaries where it makes sense, even if we later back them out for
> a better solution.

Okay, fair enough, I will commit both patches and backport them to 2.25,
2.24, and 2.23, too.

> I think that even GNU/Hurd is susceptable to these kinds of attacks
> since all modern operating systems follow the same models for stack
> and heap usage.

Windows probably gets it right, and this may have been one reason why
they never implemented C99 supported in their C compiler.  They support
alloca as an extension, but it will raise an exception in case of stack
overflow.

Thanks,
Florian