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=-0.9 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no 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 417ECC43331 for ; Wed, 25 Mar 2020 22:54:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 16B232073E for ; Wed, 25 Mar 2020 22:54:20 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=chromium.org header.i=@chromium.org header.b="GrcaqC4A" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727486AbgCYWyT (ORCPT ); Wed, 25 Mar 2020 18:54:19 -0400 Received: from mail-pf1-f196.google.com ([209.85.210.196]:42115 "EHLO mail-pf1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727358AbgCYWyT (ORCPT ); Wed, 25 Mar 2020 18:54:19 -0400 Received: by mail-pf1-f196.google.com with SMTP id 22so1790976pfa.9 for ; Wed, 25 Mar 2020 15:54:11 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=zWrlA6w6KYYZ/OQNIhCJ+kzEqHzJfgJzyL3tKc0pOFY=; b=GrcaqC4AWSa41GjxW25/ttATFM2cptZf/vbSCIUyFim8YoRmejCkibyIkocjqgOtk7 gQi2rf3Jr4vTpigiIKR03omj8m8g4PSS1/hWBn+1P66ftzknSJmfc7QPDRWJWr5fxOPH 1tgLDDziQjRk/dNQg7ElbWcilrplyXjDewFbM= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=zWrlA6w6KYYZ/OQNIhCJ+kzEqHzJfgJzyL3tKc0pOFY=; b=KLYZNpxmNs/5KjYr9pH0LUECGa1veMCN3VJVy0JlrJVaptE0LOba4kNOR/e9J5W8Uc ixjM3bTJxPXjN/kfsKmW6xw+b+G87y/nDc0a3O3BNTUeVsyks8/9/07TU8y2wrp1IBI7 Y++WZsHC01QT1giOlJjHbX5QWmlD1kjxr5CpXaSzwKxNhrSf4Nm5ymNdlJ5MfjUr9m2V qrgdwHvtsDz6+hfflaVKR60qYkchH8A774+zJ1Tu5hOKZNqpgom3VH9/q8JJDJLqp8vH TH29D9IUfjmucc1LD5ipz7++HJpua8G5jJEcZRqY9+SfbdJlE5gamVL4SIEmYvWZmLnv DR9A== X-Gm-Message-State: ANhLgQ1IhoZvBI2Oo0q8O4c3ivrfgGzPvLM/lR0fxsmHT3hGuhkVuVMj Y8b9TUvWnG2GpqYd/WtWoo9maQ== X-Google-Smtp-Source: ADFU+vsY3wfDo2Gy2J9cIPa/hwVB5bzrF7RpYHjEgTaZRdPrm7yugsdq0Qkl+UrqzZzltSS9IKTavw== X-Received: by 2002:a63:6d02:: with SMTP id i2mr5218276pgc.267.1585176850880; Wed, 25 Mar 2020 15:54:10 -0700 (PDT) Received: from www.outflux.net (smtp.outflux.net. [198.145.64.163]) by smtp.gmail.com with ESMTPSA id p70sm226890pjp.47.2020.03.25.15.54.09 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 25 Mar 2020 15:54:10 -0700 (PDT) Date: Wed, 25 Mar 2020 15:54:09 -0700 From: Kees Cook To: "Eric W. Biederman" Cc: Vlastimil Babka , Luis Chamberlain , Iurii Zaikin , linux-kernel@vger.kernel.org, linux-api@vger.kernel.org, linux-mm@kvack.org, Ivan Teterevkov , Michal Hocko , David Rientjes , Matthew Wilcox , "Guilherme G . Piccoli" Subject: Re: [RFC v2 1/2] kernel/sysctl: support setting sysctl parameters from kernel command line Message-ID: <202003251544.7ECB392A7@keescook> References: <20200325120345.12946-1-vbabka@suse.cz> <874kuc5b5z.fsf@x220.int.ebiederm.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <874kuc5b5z.fsf@x220.int.ebiederm.org> Sender: linux-api-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-api@vger.kernel.org On Wed, Mar 25, 2020 at 05:20:40PM -0500, Eric W. Biederman wrote: > Hmm. There is a big gotcha in here and I think it should be mentioned. > This code only works because no one has done set_fs(KERNEL_DS). Which > means this only works with strings that are kernel addresses essentially > by mistake. A big fat comment documenting why it is safe to pass in > kernel addresses to a function that takes a "char __user*" pointer > would be very good. Yeah, I was going to mention this too just now as I went looking through one of the handlers and was reminded that the args are marked __user. :P I suspect we might need to add some __force __user markings or something (with a comment as you say above), to keep sparse from going crazy. :) -- Kees Cook