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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id EBA8CC6FD18 for ; Wed, 29 Mar 2023 17:59:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229451AbjC2R7z (ORCPT ); Wed, 29 Mar 2023 13:59:55 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52614 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229850AbjC2R7x (ORCPT ); Wed, 29 Mar 2023 13:59:53 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 97D9F35A5 for ; Wed, 29 Mar 2023 10:59:07 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1680112746; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=Bjdk/0Vi9XEk8rAPBToebWaS2lMtqxl+/fQ8ndI4Fq4=; b=i0avLdG2wcVMcyvTwt/BEyuFgg0cGB7cIUWEIvAYVG13HYWwXwMILug0ZS+4sqDzSQR7hE +N+M/woHxsCyLfZWlxc+3pbk6tTJtTrILRwAzDJBekLZnHQltLZi9Kke4T0ojRH2+8OPSR bhAzXvYmGesj82/dDPEhMhRM3Ue3Jrk= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-203-kbDiB8jMMXGxsU4Z-OuJDA-1; Wed, 29 Mar 2023 13:59:04 -0400 X-MC-Unique: kbDiB8jMMXGxsU4Z-OuJDA-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id D201E3C0C8A6; Wed, 29 Mar 2023 17:59:03 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.45.224.161]) by smtp.corp.redhat.com (Postfix) with SMTP id B68761121330; Wed, 29 Mar 2023 17:58:59 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Wed, 29 Mar 2023 19:58:56 +0200 (CEST) Date: Wed, 29 Mar 2023 19:58:51 +0200 From: Oleg Nesterov To: Gregory Price Cc: Arnd Bergmann , Gregory Price , linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Linux-Arch , avagin@gmail.com, Peter Zijlstra , Andy Lutomirski , krisman@collabora.com, Thomas Gleixner , Jonathan Corbet , shuah , Catalin Marinas , Will Deacon , Mark Rutland , tongtiangen@huawei.com, Robin Murphy Subject: Re: [PATCH v14 1/4] asm-generic,arm64: create task variant of access_ok Message-ID: <20230329175850.GA8425@redhat.com> References: <20230328164811.2451-1-gregory.price@memverge.com> <20230328164811.2451-2-gregory.price@memverge.com> <20230329151515.GA913@redhat.com> <9a456346-e207-44e1-873e-40d21334e01b@app.fastmail.com> <20230329160322.GA4477@redhat.com> <20230329171322.GB4477@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 3.1 on 10.11.54.3 Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On 03/29, Gregory Price wrote: > > On Wed, Mar 29, 2023 at 07:13:22PM +0200, Oleg Nesterov wrote: > > > > - if (selector && !access_ok(selector, sizeof(*selector))) > > - return -EFAULT; > > - > > break; > > default: > > return -EINVAL; > > > > The result of this would be either a task calling via prctl or a tracer > calling via ptrace would be capable of setting selector to a bad pointer > and producing a SIGSEGV on the next system call. Yes, > It's a pretty small footgun, but maybe that's reasonable? I hope this is reasonable, > From a user perspective, debugging this behavior would be nightmarish. > Your call to prctl/ptrace would succeed and the process would continue > to execute until the next syscall - at which point you incur a SIGSEGV, Yes. But how does this differ from the case when, for example, user does prtcl(PR_SET_SYSCALL_USER_DISPATCH, selector = 1) ? Or another bad address < TASK_SIZE? access_ok() will happily succeed, then later syscall_user_dispatch() will equally trigger SIGSEGV. Oleg.