On Fri, Jul 4, 2014 at 10:34 PM, Amit Shah <amit.shah@xxxxxxxxxx> wrote:
> Commit d9e7972619334 "hwrng: add randomness to system from rng sources"
> added a call to rng_get_data() from the hwrng_register() function.
> However, some rng devices need initialization before data can be read
> from them.
>
> This commit makes the call to rng_get_data() depend on no init fn
> pointer being registered by the device. If an init function is
> registered, this call is made after device init.
Thanks, this seems pretty reasonable. One side-effect is that cycling
between hwrngs via sysfs (when they have init functions) will cause
them to add more entropy. I don't think this is a problem, but it is
kind of a weird side-effect.
Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
-Kees
>
> CC: Kees Cook <keescook@xxxxxxxxxxxx>
> CC: Jason Cooper <jason@xxxxxxxxxxxxxx>
> CC: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
> CC: <stable@xxxxxxxxxxxxxxx> # For v3.15+
> Signed-off-by: Amit Shah <amit.shah@xxxxxxxxxx>
> ---
> drivers/char/hw_random/core.c | 31 +++++++++++++++++++++++++------
> 1 file changed, 25 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c
> index 334601c..df95e2f 100644
> --- a/drivers/char/hw_random/core.c
> +++ b/drivers/char/hw_random/core.c
> @@ -55,16 +55,37 @@ static DEFINE_MUTEX(rng_mutex);
> static int data_avail;
> static u8 *rng_buffer;
>
> +static inline int rng_get_data(struct hwrng *rng, u8 *buffer, size_t size,
> + int wait);
> +
> static size_t rng_buffer_size(void)
> {
> return SMP_CACHE_BYTES < 32 ? 32 : SMP_CACHE_BYTES;
> }
>
> +static void add_early_randomness(struct hwrng *rng)
> +{
> + unsigned char bytes[16];
> + int bytes_read;
> +
> + bytes_read = rng_get_data(rng, bytes, sizeof(bytes), 1);
> + if (bytes_read > 0)
> + add_device_randomness(bytes, bytes_read);
> +}
> +
> static inline int hwrng_init(struct hwrng *rng)
> {
> + int ret;
> +
> if (!rng->init)
> return 0;
> - return rng->init(rng);
> +
> + ret = rng->init(rng);
> + if (ret)
> + return ret;
> +
> + add_early_randomness(rng);
> + return ret;
> }
>
> static inline void hwrng_cleanup(struct hwrng *rng)
> @@ -304,8 +325,6 @@ int hwrng_register(struct hwrng *rng)
> {
> int err = -EINVAL;
> struct hwrng *old_rng, *tmp;
> - unsigned char bytes[16];
> - int bytes_read;
>
> if (rng->name == NULL ||
> (rng->data_read == NULL && rng->read == NULL))
> @@ -347,9 +366,9 @@ int hwrng_register(struct hwrng *rng)
> INIT_LIST_HEAD(&rng->list);
> list_add_tail(&rng->list, &rng_list);
>
> - bytes_read = rng_get_data(rng, bytes, sizeof(bytes), 1);
> - if (bytes_read > 0)
> - add_device_randomness(bytes, bytes_read);
> + if (!rng->init)
> + add_early_randomness(rng);
> +
> out_unlock:
> mutex_unlock(&rng_mutex);
> out:
> --
> 1.9.3
>
--
Kees Cook
Chrome OS Security
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