From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2661EC2BA19 for ; Thu, 16 Apr 2020 02:17:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E77D720656 for ; Thu, 16 Apr 2020 02:17:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1587003435; bh=7jbHIbkIv+g7KwSbl0G4SwQ+s3EbSDnsxuzrtjKoAkE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=ULVZ0ODDdUD/r7tK9LiTvwi9BCxcfvZZ1N9cotVUDiXtkjyw/lkqF9ilaG7ymjbUn R0rieyojSRUTnRO5+xPl97kPm5sbY6v8Yw7ohxRmg0ZPVgxexQzn7TYxhUzLOQcpok 3oswe7UaHc2RQokE45Vg1WSFCqkNBeZrnnzPWNZQ= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732044AbgDPCRN (ORCPT ); Wed, 15 Apr 2020 22:17:13 -0400 Received: from mail.kernel.org ([198.145.29.99]:34308 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732005AbgDPCRH (ORCPT ); Wed, 15 Apr 2020 22:17:07 -0400 Received: from sol.localdomain (c-107-3-166-239.hsd1.ca.comcast.net [107.3.166.239]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 6320A20656; Thu, 16 Apr 2020 02:17:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1587003425; bh=7jbHIbkIv+g7KwSbl0G4SwQ+s3EbSDnsxuzrtjKoAkE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=vuojUktZ+aZ0sgh2r1xUOcuxkaqXBRVoYIySFcbjU4d+99EUVZSMPiYl9Pp4ubLeg CshgWl4eWJIRP0iC25Ks7DmXqGlZa7pJMJ8O3kIqhdm8BX8mRT2+W2Ui/DiAUTIn+U +Q/jNYaLiSOPsTSjlwCcQnzgxcf7OdW602yH0vEE= Date: Wed, 15 Apr 2020 19:17:03 -0700 From: Eric Biggers To: Herbert Xu Cc: syzbot , davem@davemloft.net, linux-crypto@vger.kernel.org, linux-kernel@vger.kernel.org, netdev@vger.kernel.org, syzkaller-bugs@googlegroups.com Subject: Re: crypto: api - Fix use-after-free and race in crypto_spawn_alg Message-ID: <20200416021703.GD816@sol.localdomain> References: <0000000000002656a605a2a34356@google.com> <20200410060942.GA4048@gondor.apana.org.au> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200410060942.GA4048@gondor.apana.org.au> Sender: linux-crypto-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-crypto@vger.kernel.org On Fri, Apr 10, 2020 at 04:09:42PM +1000, Herbert Xu wrote: > There are two problems in crypto_spawn_alg. First of all it may > return spawn->alg even if spawn->dead is set. This results in a > double-free as detected by syzbot. > > Secondly the setting of the DYING flag is racy because we hold > the read-lock instead of the write-lock. We should instead call > crypto_shoot_alg in a safe manner by gaining a refcount, dropping > the lock, and then releasing the refcount. > > This patch fixes both problems. > > Reported-by: syzbot+fc0674cde00b66844470@syzkaller.appspotmail.com > Fixes: 4f87ee118d16 ("crypto: api - Do not zap spawn->alg") > Fixes: 73669cc55646 ("crypto: api - Fix race condition in...") > Cc: > Signed-off-by: Herbert Xu > > diff --git a/crypto/algapi.c b/crypto/algapi.c > index 69605e21af92..f8b4dc161c02 100644 > --- a/crypto/algapi.c > +++ b/crypto/algapi.c > @@ -716,17 +716,27 @@ EXPORT_SYMBOL_GPL(crypto_drop_spawn); > > static struct crypto_alg *crypto_spawn_alg(struct crypto_spawn *spawn) > { > - struct crypto_alg *alg; > + struct crypto_alg *alg = ERR_PTR(-EAGAIN); > + struct crypto_alg *target; > + bool shoot = false; > > down_read(&crypto_alg_sem); > - alg = spawn->alg; > - if (!spawn->dead && !crypto_mod_get(alg)) { > - alg->cra_flags |= CRYPTO_ALG_DYING; > - alg = NULL; > + if (!spawn->dead) { > + alg = spawn->alg; > + if (!crypto_mod_get(alg)) { > + target = crypto_alg_get(alg); > + shoot = true; > + alg = ERR_PTR(-EAGAIN); > + } > } > up_read(&crypto_alg_sem); > > - return alg ?: ERR_PTR(-EAGAIN); > + if (shoot) { > + crypto_shoot_alg(target); > + crypto_alg_put(target); > + } > + > + return alg; > } Wouldn't it be a bit simpler to set 'target = NULL', remove 'shoot', and use 'if (target)' instead of 'if (shoot)'? - Eric