Re: [PATCH 2/2] crypto: skcipher: Remove VLA usage for SKCIPHER_REQUEST_ON_STACK

[Ard Biesheuvel]

On 6 September 2018 at 10:51, Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx> wrote:
> On Thu, Sep 06, 2018 at 10:11:59AM +0200, Ard Biesheuvel wrote:
>>
>> That way, we will almost certainly oops on a NULL pointer dereference
>> right after, but we at least the stack corruption.
>
> A crash is just as bad as a BUG_ON.
>
> Is this even a real problem? Do we have any users of this construct
> that is using it on async algorithms?
>

Perhaps not, but it is not enforced atm.

In any case, limiting the reqsize is going to break things, so that
needs to occur based on the sync/async nature of the algo. That also
means we'll corrupt the stack if we ever end up using
SKCIPHER_REQUEST_ON_STACK() with an async algo whose reqsize is
greater than the sync reqsize limit, so I do think some additional
sanity check is appropriate.