On Tue, Mar 19, 2013 at 12:18:09PM -0400, Jarod Wilson wrote:
> Commit ec8f02da9e added priming of last_data per fips requirements.
> Unfortuantely, it did so in a way that can lead to multiple threads all
> incrementing nbytes, but only one actually doing anything with the extra
> data, which leads to some fun  random corruption and panics.
> 
> The fix is to simply do everything needed to prime last_data in a single
> shot, so there's no window for multiple cpus to increment nbytes -- in
> fact, we won't even increment or decrement nbytes anymore, we'll just
> extract the needed EXTRACT_BYTES one time per pool and then carry on with
> the normal routine.
> 
> All these changes have been tested across multiple hosts and architectures
> where panics were previously encoutered. The code changes are are strictly
> limited to areas only touched when when booted in fips mode.
> 
> This change should also go into 3.8-stable, to make the myriads of fips
> users on 3.8.x happy.
> 
> Tested-by: Jan Stancek <jstan...@redhat.com>
> Tested-by: Jan Stodola <jstod...@redhat.com>
> CC: Herbert Xu <herb...@gondor.apana.org.au>
> CC: Neil Horman <nhor...@tuxdriver.com>
> CC: "David S. Miller" <da...@davemloft.net>
> CC: Matt Mackall <m...@selenic.com>
> CC: "Theodore Ts'o" <ty...@mit.edu>
> CC: linux-crypto@vger.kernel.org
> CC: sta...@vger.kernel.org
> Signed-off-by: Jarod Wilson <ja...@redhat.com>
> ---
>  drivers/char/random.c |   30 +++++++++++++++---------------
>  1 files changed, 15 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/char/random.c b/drivers/char/random.c
> index 85e81ec..15e5a2b 100644
> --- a/drivers/char/random.c
> +++ b/drivers/char/random.c
> @@ -953,10 +953,23 @@ static ssize_t extract_entropy(struct entropy_store *r, 
> void *buf,
>  {
>       ssize_t ret = 0, i;
>       __u8 tmp[EXTRACT_SIZE];
> +     unsigned long flags;
>  
>       /* if last_data isn't primed, we need EXTRACT_SIZE extra bytes */
> -     if (fips_enabled && !r->last_data_init)
> -             nbytes += EXTRACT_SIZE;
> +     if (fips_enabled) {
> +             spin_lock_irqsave(&r->lock, flags);
> +             if (!r->last_data_init) {
> +                     r->last_data_init = true;
> +                     spin_unlock_irqrestore(&r->lock, flags);
> +                     trace_extract_entropy(r->name, EXTRACT_SIZE,
> +                                           r->entropy_count, _RET_IP_);
> +                     xfer_secondary_pool(r, EXTRACT_SIZE);
> +                     extract_buf(r, tmp);
> +                     spin_lock_irqsave(&r->lock, flags);
> +                     memcpy(r->last_data, tmp, EXTRACT_SIZE);
> +             }
> +             spin_unlock_irqrestore(&r->lock, flags);
> +     }
>  
>       trace_extract_entropy(r->name, nbytes, r->entropy_count, _RET_IP_);
>       xfer_secondary_pool(r, nbytes);
> @@ -966,19 +979,6 @@ static ssize_t extract_entropy(struct entropy_store *r, 
> void *buf,
>               extract_buf(r, tmp);
>  
>               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");
> -- 
> 1.7.1
> 
> 
Acked-by: Neil Horman <nhor...@tuxdriver.com>

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