crypto: drbg - Clean up generation code

A few miscellaneous cleanups to make the code a bit more readable:

  - Replace (buf, buflen) with (out, outlen)
  - Update (out, outlen) as we go along
  - Use size_t for lengths
  - Use min()
  - Adjust some comments and log messages
  - Rename a variable named 'len' to 'err', since it isn't a length

Signed-off-by: Eric Biggers <ebiggers@kernel.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

diff --git a/crypto/drbg.c b/crypto/drbg.c
index bab766026177a37bf2b0569149b6cd2fef3985ae..b54c807930af88675fe9cebcdb8357c774bd042a 100644 (file)
--- a/crypto/drbg.c
+++ b/crypto/drbg.c
@@ -180,12 +180,9 @@ static void drbg_hmac_update(struct drbg_state *drbg,
 }
 
 /* generate function of HMAC DRBG as defined in 10.1.2.5 */
-static void drbg_hmac_generate(struct drbg_state *drbg,
-                              unsigned char *buf,
-                              unsigned int buflen,
+static void drbg_hmac_generate(struct drbg_state *drbg, u8 *out, size_t outlen,
                               const u8 *addtl1, size_t addtl1_len)
 {
-       int len = 0;
        u8 addtl2[32];
        size_t addtl2_len = 0;
 
@@ -210,17 +207,16 @@ static void drbg_hmac_generate(struct drbg_state *drbg,
        if (addtl1_len || addtl2_len)
                drbg_hmac_update(drbg, addtl1, addtl1_len, addtl2, addtl2_len);
 
-       while (len < buflen) {
-               unsigned int outlen = 0;
+       while (outlen) {
+               size_t n = min(DRBG_STATE_LEN, outlen);
 
                /* 10.1.2.5 step 4.1 */
                hmac_sha512(&drbg->key, drbg->V, DRBG_STATE_LEN, drbg->V);
-               outlen = (DRBG_STATE_LEN < (buflen - len)) ?
-                         DRBG_STATE_LEN : (buflen - len);
 
                /* 10.1.2.5 step 4.2 */
-               memcpy(buf + len, drbg->V, outlen);
-               len += outlen;
+               memcpy(out, drbg->V, n);
+               out += n;
+               outlen -= n;
        }
 
        /* 10.1.2.5 step 6 */
@@ -331,31 +327,27 @@ out:
 }
 
 /*
- * DRBG generate function as required by SP800-90A - this function
- * generates random numbers
+ * Generate random bytes from an SP800-90A DRBG.
  *
  * @drbg DRBG state handle
- * @buf Buffer where to store the random numbers -- the buffer must already
- *      be pre-allocated by caller
- * @buflen Length of output buffer - this value defines the number of random
- *        bytes pulled from DRBG
+ * @out Buffer where to store the random bytes
+ * @outlen Number of random bytes to generate
  * @addtl Optional additional input that is mixed into state
  * @addtl_len Length of @addtl in bytes, may be 0
  *
  * return: 0 when all bytes are generated; < 0 in case of an error
  */
-static int drbg_generate(struct drbg_state *drbg,
-                        unsigned char *buf, unsigned int buflen,
+static int drbg_generate(struct drbg_state *drbg, u8 *out, size_t outlen,
                         const u8 *addtl, size_t addtl_len)
        __must_hold(&drbg->drbg_mutex)
 {
-       int len = 0;
+       int err;
 
        if (!drbg->instantiated) {
                pr_devel("DRBG: not yet instantiated\n");
                return -EINVAL;
        }
-       if (0 == buflen || !buf) {
+       if (out == NULL || outlen == 0) {
                pr_devel("DRBG: no output buffer provided\n");
                return -EINVAL;
        }
@@ -365,9 +357,8 @@ static int drbg_generate(struct drbg_state *drbg,
        }
 
        /* 9.3.1 step 2 */
-       if (buflen > DRBG_MAX_REQUEST_BYTES) {
-               pr_devel("DRBG: requested random numbers too large %u\n",
-                        buflen);
+       if (outlen > DRBG_MAX_REQUEST_BYTES) {
+               pr_devel("DRBG: request length is too long %zu\n", outlen);
                return -EINVAL;
        }
 
@@ -393,16 +384,16 @@ static int drbg_generate(struct drbg_state *drbg,
                pr_devel("DRBG: reseeding before generation (prediction resistance: %s)\n",
                         str_true_false(drbg->pr));
                /* 9.3.1 steps 7.1 through 7.3 */
-               len = drbg_seed(drbg, addtl, addtl_len, true);
-               if (len)
-                       goto err;
+               err = drbg_seed(drbg, addtl, addtl_len, true);
+               if (err)
+                       return err;
                /* 9.3.1 step 7.4 */
                addtl = NULL;
                addtl_len = 0;
        }
 
        /* 9.3.1 step 8 and 10 */
-       drbg_hmac_generate(drbg, buf, buflen, addtl, addtl_len);
+       drbg_hmac_generate(drbg, out, outlen, addtl, addtl_len);
 
        /* 10.1.2.5 step 7 */
        drbg->reseed_ctr++;
@@ -420,13 +411,7 @@ static int drbg_generate(struct drbg_state *drbg,
         * correct operation of the DRBG.
         */
 
-       /*
-        * All operations were successful, return 0 as mandated by
-        * the kernel crypto API interface.
-        */
-       len = 0;
-err:
-       return len;
+       return 0;
 }
 
 /***************************************************************