[PATCH 3.15 091/109] hwrng: fetch randomness only after device init

Greg Kroah-Hartman
2014-07-26T19:25:22Z

From: Amit Shah <amit.shah@redhat.com>

commit d3cc7996473a7bdd33256029988ea690754e4e2a upstream.

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.

CC: Kees Cook <keescook@chromium.org>
CC: Jason Cooper <jason@lakedaemon.net>
CC: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Amit Shah <amit.shah@redhat.com>
Reviewed-by: Jason Cooper <jason@lakedaemon.net>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/char/hw_random/core.c | 41 +++++++++++++++++++++++++++++++++--------
1 file changed, 33 insertions(+), 8 deletions(-)

--- a/drivers/char/hw_random/core.c
+++ b/drivers/char/hw_random/core.c
@@ -55,16 +55,35 @@ 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)
{
- if (!rng->init)
- return 0;
- return rng->init(rng);
+ if (rng->init) {
+ int ret;
+
+ ret = rng->init(rng);
+ if (ret)
+ return ret;
+ }
+ add_early_randomness(rng);
+ return 0;
}

static inline void hwrng_cleanup(struct hwrng *rng)
@@ -304,8 +323,6 @@ 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 +364,17 @@ 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 (old_rng && !rng->init) {
+ /*
+ * Use a new device's input to add some randomness to
+ * the system. If this rng device isn't going to be
+ * used right away, its init function hasn't been
+ * called yet; so only use the randomness from devices
+ * that don't need an init callback.
+ */
+ add_early_randomness(rng);
+ }
+
out_unlock:
mutex_unlock(&rng_mutex);