crypto: atmel-sha204a - Set hwrng quality to lowest possible

commit 8006aff15516a170640239c5a8e6696c0ba18d8e upstream.

According to the review by Bill Cox [1], the Atmel SHA204A random number
generator produces random numbers with very low entropy.

Set the lowest possible entropy for this chip just to be safe.

[1] https://www.metzdowd.com/pipermail/cryptography/2014-December/023858.html

Fixes: da001fb651b00e1d ("crypto: atmel-i2c - add support for SHA204A random number generator")
Cc: <stable@vger.kernel.org>
Signed-off-by: Marek Behún <kabel@kernel.org>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Marek Behún <kabel@kernel.org>

diff --git a/drivers/crypto/atmel-sha204a.c b/drivers/crypto/atmel-sha204a.c
index c96c14e7dab1c0ae89fd026bb733155cf761659c..0ef92109ce22a32921a924d435dd363e62b8f72b 100644 (file)
--- a/drivers/crypto/atmel-sha204a.c
+++ b/drivers/crypto/atmel-sha204a.c
@@ -107,7 +107,12 @@ static int atmel_sha204a_probe(struct i2c_client *client,
 
        i2c_priv->hwrng.name = dev_name(&client->dev);
        i2c_priv->hwrng.read = atmel_sha204a_rng_read;
-       i2c_priv->hwrng.quality = 1024;
+
+       /*
+        * According to review by Bill Cox [1], this HWRNG has very low entropy.
+        * [1] https://www.metzdowd.com/pipermail/cryptography/2014-December/023858.html
+        */
+       i2c_priv->hwrng.quality = 1;
 
        ret = devm_hwrng_register(&client->dev, &i2c_priv->hwrng);
        if (ret)