netdev - Re: [PATCH] mac80211: port CCMP to cryptoapi's CCM driver

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Date:	Tue, 8 Oct 2013 15:41:33 +0200
From:	Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:	David Laight <David.Laight@...LAB.COM>
Cc:	Johannes Berg <johannes@...solutions.net>,
	"<linux-wireless@...r.kernel.org>" <linux-wireless@...r.kernel.org>,
	"<netdev@...r.kernel.org>" <netdev@...r.kernel.org>,
	"<patches@...aro.org>" <patches@...aro.org>,
	"<linville@...driver.com>" <linville@...driver.com>
Subject: Re: [PATCH] mac80211: port CCMP to cryptoapi's CCM driver



On 8 okt. 2013, at 15:01, "David Laight" <David.Laight@...LAB.COM> wrote:

>> Hmm, thanks I guess. I'll need to review this in more detail, but I have
>> a question first:
>> 
>>> +    /* allocate the variable sized aead_request on the stack */
>>> +    int l = DIV_ROUND_UP(crypto_aead_reqsize(tfm),
>>> +                 sizeof(struct aead_request));
>>> +    struct aead_request req[1 + l];
>> 
>> This looks a bit odd, why round up first and then add one? Why even
>> bother using a struct array rather than some local struct like
> 
> Is it even a good idea to be allocating variable sized items
> on the kernel stack?
> 
> There has to be enough stack available for the maximum number
> of entries - so there is little point in dynamically sizing it.

Actually, as the size is always the same, it should be feasible to alloc a couple of request structs at init time. would one for rx and one for tx be sufficient? or is this code more reentrant than that?

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