From mboxrd@z Thu Jan 1 00:00:00 1970 From: Neil Horman Subject: [PATCH] ansi_cprng: Fix off by one error in non-block size request Date: Tue, 17 Sep 2013 08:33:11 -0400 Message-ID: <1379421191-13740-1-git-send-email-nhorman@tuxdriver.com> Cc: Neil Horman , Stephan Mueller , Petr Matousek , Herbert Xu , "David S. Miller" To: linux-crypto@vger.kernel.org Return-path: Received: from charlotte.tuxdriver.com ([70.61.120.58]:41894 "EHLO smtp.tuxdriver.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752418Ab3IQMdr (ORCPT ); Tue, 17 Sep 2013 08:33:47 -0400 Sender: linux-crypto-owner@vger.kernel.org List-ID: Stephan Mueller reported to me recently a error in random number generation in the ansi cprng. If several small requests are made that are less than the instances block size, the remainder for loop code doesn't increment rand_data_valid in the last iteration, meaning that the last bytes in the rand_data buffer gets reused on the subsequent smaller-than-a-block request for random data. The fix is pretty easy, just re-code the for loop to make sure that rand_data_valid gets incremented appropriately Signed-off-by: Neil Horman Reported-by: Stephan Mueller CC: Stephan Mueller CC: Petr Matousek CC: Herbert Xu CC: "David S. Miller" --- crypto/ansi_cprng.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/crypto/ansi_cprng.c b/crypto/ansi_cprng.c index c0bb377..666f196 100644 --- a/crypto/ansi_cprng.c +++ b/crypto/ansi_cprng.c @@ -230,11 +230,11 @@ remainder: */ if (byte_count < DEFAULT_BLK_SZ) { empty_rbuf: - for (; ctx->rand_data_valid < DEFAULT_BLK_SZ; - ctx->rand_data_valid++) { + while (ctx->rand_data_valid < DEFAULT_BLK_SZ) { *ptr = ctx->rand_data[ctx->rand_data_valid]; ptr++; byte_count--; + ctx->rand_data_valid++; if (byte_count == 0) goto done; } -- 1.8.3.1