From patchwork Wed Jun 7 23:26:07 2017 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Jason A. Donenfeld" X-Patchwork-Id: 9773267 X-Patchwork-Delegate: herbert@gondor.apana.org.au Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id 0DCB360234 for ; Wed, 7 Jun 2017 23:27:07 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id F26CC283AD for ; Wed, 7 Jun 2017 23:27:06 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id E4AE92848D; Wed, 7 Jun 2017 23:27:06 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.0 required=2.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, RCVD_IN_DNSWL_HI autolearn=unavailable version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 8F621283AD for ; Wed, 7 Jun 2017 23:27:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752772AbdFGX0u (ORCPT ); Wed, 7 Jun 2017 19:26:50 -0400 Received: from frisell.zx2c4.com ([192.95.5.64]:55513 "EHLO frisell.zx2c4.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753542AbdFGX0s (ORCPT ); Wed, 7 Jun 2017 19:26:48 -0400 Received: by frisell.zx2c4.com (ZX2C4 Mail Server) with ESMTP id 7716f94d; Wed, 7 Jun 2017 23:26:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha1; c=relaxed; d=zx2c4.com; h=from:to:cc :subject:date:message-id:in-reply-to:references; s=mail; bh=9Goi ZmIRjfE9pg+53xr8d7uaU6k=; b=1z2g3F6i6f4/tpjOrgC8q62S0GdCOqQ+PErK bee7QDbouXM5jXK7chZFP2VpqiN6nb1oONMCCmS33ooCpXqLL6D0/ggweRmi3+UT Jrm3QD0O1PNPjD39pyKlaMeB9GMwBmA9zCpei/6kI9ANunnUsul9DkHUkNi3czJK QEt6w8Um4rdoMIwdwIJqrZ/e9FlLBxmgPcXboippoiIzZNMbrkgVSmOHgPKqyN9W oFeDpPs5HCy2XwjxdeECvjTK423PFc7a7X8pdquyJRwx53myNG2PWeOQgUHkh6X2 RLzYC/4CRZkFACdnndxwVbgzm5mdExmPkRnEyrifqQ21bQsLFw== Received: by frisell.zx2c4.com (ZX2C4 Mail Server) with ESMTPSA id a5b6150b (TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256:NO); Wed, 7 Jun 2017 23:26:11 +0000 (UTC) From: "Jason A. Donenfeld" To: Theodore Ts'o , Linux Crypto Mailing List , LKML , kernel-hardening@lists.openwall.com, Greg Kroah-Hartman , Eric Biggers , Linus Torvalds , David Miller Cc: "Jason A. Donenfeld" Subject: [PATCH v5 13/13] random: warn when kernel uses unseeded randomness Date: Thu, 8 Jun 2017 01:26:07 +0200 Message-Id: <20170607232607.26870-14-Jason@zx2c4.com> In-Reply-To: <20170607232607.26870-1-Jason@zx2c4.com> References: <20170607232607.26870-1-Jason@zx2c4.com> Sender: linux-crypto-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-crypto@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP This enables an important dmesg notification about when drivers have used the crng without it being seeded first. Prior, these errors would occur silently, and so there hasn't been a great way of diagnosing these types of bugs for obscure setups. By adding this as a config option, we can leave it on by default, so that we learn where these issues happen, in the field, will still allowing some people to turn it off, if they really know what they're doing and do not want the log entries. However, we don't leave it _completely_ by default. An earlier version of this patch simply had `default y`. I'd really love that, but it turns out, this problem with unseeded randomness being used is really quite present and is going to take a long time to fix. Thus, as a compromise between log-messages-for-all and nobody-knows, this is `default y`, except it is also `depends on DEBUG_KERNEL`. This will ensure that the curious see the messages while others don't have to. Signed-off-by: Jason A. Donenfeld --- drivers/char/random.c | 15 +++++++++++++-- lib/Kconfig.debug | 16 ++++++++++++++++ 2 files changed, 29 insertions(+), 2 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index 77587ac1ecb2..5252690610ec 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -288,7 +288,6 @@ #define SEC_XFER_SIZE 512 #define EXTRACT_SIZE 10 -#define DEBUG_RANDOM_BOOT 0 #define LONGS(x) (((x) + sizeof(unsigned long) - 1)/sizeof(unsigned long)) @@ -1481,7 +1480,7 @@ void get_random_bytes(void *buf, int nbytes) { __u8 tmp[CHACHA20_BLOCK_SIZE]; -#if DEBUG_RANDOM_BOOT > 0 +#ifdef CONFIG_WARN_UNSEEDED_RANDOM if (!crng_ready()) printk(KERN_NOTICE "random: %pF get_random_bytes called " "with crng_init = %d\n", (void *) _RET_IP_, crng_init); @@ -2075,6 +2074,12 @@ u64 get_random_u64(void) return ret; #endif +#ifdef CONFIG_WARN_UNSEEDED_RANDOM + if (!crng_ready()) + printk(KERN_NOTICE "random: %pF get_random_u64 called " + "with crng_init = %d\n", (void *) _RET_IP_, crng_init); +#endif + batch = &get_cpu_var(batched_entropy_u64); if (use_lock) read_lock_irqsave(&batched_entropy_reset_lock, flags); @@ -2101,6 +2106,12 @@ u32 get_random_u32(void) if (arch_get_random_int(&ret)) return ret; +#ifdef CONFIG_WARN_UNSEEDED_RANDOM + if (!crng_ready()) + printk(KERN_NOTICE "random: %pF get_random_u32 called " + "with crng_init = %d\n", (void *) _RET_IP_, crng_init); +#endif + batch = &get_cpu_var(batched_entropy_u32); if (use_lock) read_lock_irqsave(&batched_entropy_reset_lock, flags); diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index e4587ebe52c7..c4159605bfbf 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -1209,6 +1209,22 @@ config STACKTRACE It is also used by various kernel debugging features that require stack trace generation. +config WARN_UNSEEDED_RANDOM + bool "Warn when kernel uses unseeded randomness" + default y + depends on DEBUG_KERNEL + help + Some parts of the kernel contain bugs relating to their use of + cryptographically secure random numbers before it's actually possible + to generate those numbers securely. This setting ensures that these + flaws don't go unnoticed, by enabling a message, should this ever + occur. This will allow people with obscure setups to know when things + are going wrong, so that they might contact developers about fixing + it. + + Say Y here, unless you simply do not care about using unseeded + randomness and do not want a potential warning message in your logs. + config DEBUG_KOBJECT bool "kobject debugging" depends on DEBUG_KERNEL