crypto: rng - RNGs must return 0 in success case

Change the RNGs to always return 0 in success case.

This patch ensures that seqiv.c works with RNGs other than krng. seqiv
expects that any return code other than 0 is an error. Without the
patch, rfc4106(gcm(aes)) will not work when using a DRBG or an ANSI
X9.31 RNG.
Signed-off-by: Stephan Mueller <smueller@chronox.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

crypto/ansi_cprng.c

@@ -210,7 +210,11 @@ static int get_prng_bytes(char *buf, size_t nbytes, struct prng_context *ctx,
 		byte_count = DEFAULT_BLK_SZ;
 	}
 
-	err = byte_count;
+	/*
+	 * Return 0 in case of success as mandated by the kernel
+	 * crypto API interface definition.
+	 */
+	err = 0;
 
 	dbgprint(KERN_CRIT "getting %d random bytes for context %p\n",
 		byte_count, ctx);

crypto/drbg.c

@@ -1280,7 +1280,7 @@ static void drbg_restore_shadow(struct drbg_state *drbg,
  *	  as defined in SP800-90A. The additional input is mixed into
  *	  the state in addition to the pulled entropy.
  *
- * return: generated number of bytes
+ * 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,
@@ -1419,6 +1419,11 @@ static int drbg_generate(struct drbg_state *drbg,
 	}
 #endif
 
+	/*
+	 * All operations were successful, return 0 as mandated by
+	 * the kernel crypto API interface.
+	 */
+	len = 0;
 err:
 	shadow->d_ops->crypto_fini(shadow);
 	drbg_restore_shadow(drbg, &shadow);

include/crypto/rng.h

@@ -103,8 +103,7 @@ static inline void crypto_free_rng(struct crypto_rng *tfm)
  * This function fills the caller-allocated buffer with random numbers using the
  * random number generator referenced by the cipher handle.
  *
- * Return: > 0 function was successful and returns the number of generated
- *	   bytes; < 0 if an error occurred
+ * Return: 0 function was successful; < 0 if an error occurred
  */
 static inline int crypto_rng_get_bytes(struct crypto_rng *tfm,
 				       u8 *rdata, unsigned int dlen)