Re: alloca() in kernel code

[Johnny Billquist <bqt%softjar.se@localhost>]

On 2019-10-12 20:47, Joerg Sonnenberger wrote:
> On Sat, Oct 12, 2019 at 08:13:25PM +0200, Johnny Billquist wrote:
> > On 2019-10-12 19:01, Emmanuel Dreyfus wrote:
> > > Mouse <mouse%Rodents-Montreal.ORG@localhost> wrote:
> > >
> > > > I'm presumably missing something here, but what?
> > >
> > > I suspect Maxime's concern is about uncontrolled stack-based variable
> > > buffer, which could be used to crash the kernel.
> > >
> > > But in my case, the data is coming from the bootloader. I cannot think
> > > about a scenario where it makes sense to defend against an attack from
> > > the bootloader. The kernel already has absolute trust in the bootloader.
> >
> > On this one, I agree with Maxime.
> >
> > Even if it comes from the bootloader, why would you want to use alloca()?
>
> Because as Emmanuel wrote initially, dynamic allocations might not be
> possible yet.

But if you use alloca(), you will have to check what size you'd like to 
allocate, and not allocate more than some maximum amount, I would 
assume. Or do you really think that it is ok to just let it try no 
matter what amount is decided you want to allocate?

And if you figure out an upper limit, then you might as well just define 
an array of that size in the function, and be done with it.

  Johnny

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Johnny Billquist                  || "I'm on a bus
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