linux-kernel - Re: [PATCH v6 1/5] random: Blocking API for accessing nonblocking

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Date:	Mon, 18 May 2015 15:26:13 +0200
From:	Stephan Mueller <smueller@...onox.de>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	pebolle@...cali.nl, andreas.steffen@...ongswan.org, tytso@....edu,
	sandyinchina@...il.com, linux-kernel@...r.kernel.org,
	linux-crypto@...r.kernel.org
Subject: Re: [PATCH v6 1/5] random: Blocking API for accessing nonblocking_pool

Am Montag, 18. Mai 2015, 15:07:10 schrieb Stephan Mueller:

Hi Herbert,

>>
>>You can simplify this further and get rid of buf/nbytes.  All
>>we need to know is whether the pool is ready.  Everything else
>>can come from private.
>
>So, the async function is now just a notification of the caller. Sounds good
>with me.
>

I am just running into an interesting problem with a missing cancel operation: 
a caller instantiates a DRBG handle and invokes the seeding operation. The 
nonblocking_pool is not initialized. Therefore, the callback is put onto the 
list for being processed later.

Now, the caller releases the DRBG handle *before* the callback is triggered.

The callback is triggered with a pointer that is invalid, but the pointer is 
non-NULL. Therefore, I am not sure how to validate the pointer in the callback 
function.

I would think that there is no other way than to add a cancel API call that 
allows removing a list entry from the wait list.

Ciao
Stephan
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