crypto: rng - RNGs must return 0 in success case

commit cde001e4 upstream.

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>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>

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);