Re: [PATCH v3] random: prime last_data value per fips requirements

[Neil Horman]

On Tue, Nov 06, 2012 at 10:42:42AM -0500, Jarod Wilson wrote:
> The value stored in last_data must be primed for FIPS 140-2 purposes. Upon
> first use, either on system startup or after an RNDCLEARPOOL ioctl, we
> need to take an initial random sample, store it internally in last_data,
> then pass along the value after that to the requester, so that consistency
> checks aren't being run against stale and possibly known data.
> 
> v2: streamline code flow a bit, eliminating extra loop and spinlock in the
> case where we need to prime, and account for the extra primer bits.
> 
> v3: extract_buf() can't be called with spinlock already held, so bring
> back some extra lock/unlock calls.
> 
> CC: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
> CC: "David S. Miller" <davem@xxxxxxxxxxxxx>
> CC: Neil Horman <nhorman@xxxxxxxxxxxxx>
> CC: Matt Mackall <mpm@xxxxxxxxxxx>
> CC: linux-crypto@xxxxxxxxxxxxxxx
> Signed-off-by: Jarod Wilson <jarod@xxxxxxxxxx>
> ---
>  drivers/char/random.c |   17 +++++++++++++++++
>  1 files changed, 17 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/char/random.c b/drivers/char/random.c
> index b86eae9..d0139df 100644
> --- a/drivers/char/random.c
> +++ b/drivers/char/random.c
> @@ -437,6 +437,7 @@ struct entropy_store {
>  	int entropy_count;
>  	int entropy_total;
>  	unsigned int initialized:1;
> +	bool last_data_init;
>  	__u8 last_data[EXTRACT_SIZE];
>  };
>  
> @@ -957,6 +958,10 @@ static ssize_t extract_entropy(struct entropy_store *r, void *buf,
>  	ssize_t ret = 0, i;
>  	__u8 tmp[EXTRACT_SIZE];
>  
> +	/* if last_data isn't primed, we need EXTRACT_SIZE extra bytes */
> +	if (fips_enabled && !r->last_data_init)
> +		nbytes += EXTRACT_SIZE;
> +
>  	trace_extract_entropy(r->name, nbytes, r->entropy_count, _RET_IP_);
>  	xfer_secondary_pool(r, nbytes);
>  	nbytes = account(r, nbytes, min, reserved);
> @@ -967,6 +972,17 @@ static ssize_t extract_entropy(struct entropy_store *r, void *buf,
>  		if (fips_enabled) {
>  			unsigned long flags;
>  
> +
> +			/* prime last_data value if need be, per fips 140-2 */
> +			if (!r->last_data_init) {
> +				spin_lock_irqsave(&r->lock, flags);
> +				memcpy(r->last_data, tmp, EXTRACT_SIZE);
> +				r->last_data_init = true;
> +				nbytes -= EXTRACT_SIZE;
> +				spin_unlock_irqrestore(&r->lock, flags);
> +				extract_buf(r, tmp);
> +			}
> +
>  			spin_lock_irqsave(&r->lock, flags);
>  			if (!memcmp(tmp, r->last_data, EXTRACT_SIZE))
>  				panic("Hardware RNG duplicated output!\n");
> @@ -1086,6 +1102,7 @@ static void init_std_data(struct entropy_store *r)
>  
>  	r->entropy_count = 0;
>  	r->entropy_total = 0;
> +	r->last_data_init = false;
>  	mix_pool_bytes(r, &now, sizeof(now), NULL);
>  	for (i = r->poolinfo->POOLBYTES; i > 0; i -= sizeof(rv)) {
>  		if (!arch_get_random_long(&rv))
> -- 
> 1.7.1
> 
> 
Thanks Jarod.
Acked-by: Neil Horman <nhorman@xxxxxxxxxxxxx>

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