crypto: ansi_cprng - Allow resetting of DT value

	This is a patch that was sent to me by Jarod Wilson, marking off my
outstanding todo to allow the ansi cprng to set/reset the DT counter value in a
cprng instance.  Currently crytpo_rng_reset accepts a seed byte array which is
interpreted by the ansi_cprng as a {V key} tuple.  This patch extends that tuple
to now be {V key DT}, with DT an optional value during reset.  This patch also
fixes  a bug we noticed in which the offset of the key area of the seed is
started at DEFAULT_PRNG_KSZ rather than DEFAULT_BLK_SZ as it should be.

Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
Signed-off-by: Jarod Wilson <jarod@redhat.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

1 files changed, 13 insertions, 3 deletions

diff --git a/crypto/ansi_cprng.c b/crypto/ansi_cprng.c
index 72db0fd763cc..486aa93646f7 100644
--- a/crypto/ansi_cprng.c
+++ b/crypto/ansi_cprng.c
@@ -349,15 +349,25 @@ static int cprng_get_random(struct crypto_rng *tfm, u8 *rdata,
         return get_prng_bytes(rdata, dlen, prng);
 }
 
+/*
+ *  This is the cprng_registered reset method the seed value is
+ *  interpreted as the tuple { V KEY DT}
+ *  V and KEY are required during reset, and DT is optional, detected
+ *  as being present by testing the length of the seed
+ */
 static int cprng_reset(struct crypto_rng *tfm, u8 *seed, unsigned int slen)
 {
         struct prng_context *prng = crypto_rng_ctx(tfm);
-        u8 *key = seed + DEFAULT_PRNG_KSZ;
+        u8 *key = seed + DEFAULT_BLK_SZ;
+        u8 *dt = NULL;
 
         if (slen < DEFAULT_PRNG_KSZ + DEFAULT_BLK_SZ)
                 return -EINVAL;
 
-        reset_prng_context(prng, key, DEFAULT_PRNG_KSZ, seed, NULL);
+        if (slen >= (2 * DEFAULT_BLK_SZ + DEFAULT_PRNG_KSZ))
+                dt = key + DEFAULT_PRNG_KSZ;
+
+        reset_prng_context(prng, key, DEFAULT_PRNG_KSZ, seed, dt);
 
         if (prng->flags & PRNG_NEED_RESET)
                 return -EINVAL;
@@ -379,7 +389,7 @@ static struct crypto_alg rng_alg = {
                 .rng = {
                         .rng_make_random        = cprng_get_random,
                         .rng_reset              = cprng_reset,
-                        .seedsize = DEFAULT_PRNG_KSZ + DEFAULT_BLK_SZ,
+                        .seedsize = DEFAULT_PRNG_KSZ + 2*DEFAULT_BLK_SZ,
                 }
         }
 };