From: Neil Horman Subject: [PATCH] crypto: force reset of cprng on allocation Date: Fri, 23 Jan 2009 11:50:27 -0500 Message-ID: <20090123165027.GB29548@hmsreliant.think-freely.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii To: herbert@gondor.apana.org.au, linux-crypto@vger.kernel.org, linux-kernel@vger.kernel.org Return-path: Received: from charlotte.tuxdriver.com ([70.61.120.58]:55888 "EHLO smtp.tuxdriver.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757085AbZAWQug (ORCPT ); Fri, 23 Jan 2009 11:50:36 -0500 Content-Disposition: inline Sender: linux-crypto-owner@vger.kernel.org List-ID: pseudo RNGs provide predictable outputs based on input parateters {key, V, DT}, the idea behind them is that only the user should know what the inputs are. While its nice to have default known values for testing purposes, it seems dangerous to allow the use of those default values without some sort of safety measure in place, lest an attacker easily guess the output of the cprng. This patch forces the NEED_RESET flag on when allocating a cprng context, so that any user is forced to reseed it before use. The defaults can still be used for testing, but this will prevent their inadvertent use, and be more secure. Signed-off-by: Neil Horman ansi_cprng.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) diff --git a/crypto/ansi_cprng.c b/crypto/ansi_cprng.c index 7eef5be..d9c3971 100644 --- a/crypto/ansi_cprng.c +++ b/crypto/ansi_cprng.c @@ -348,7 +348,16 @@ static int cprng_init(struct crypto_tfm *tfm) spin_lock_init(&ctx->prng_lock); - return reset_prng_context(ctx, NULL, DEFAULT_PRNG_KSZ, NULL, NULL); + if (reset_prng_context(ctx, NULL, DEFAULT_PRNG_KSZ, NULL, NULL) < 0) + return -EINVAL; + + /* + * after allocation, we should always force the user to reset + * so they don't inadvertently use the insecure default values + * without specifying them intentially + */ + ctx->flags |= PRNG_NEED_RESET; + return 0; } static void cprng_exit(struct crypto_tfm *tfm)