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=-6.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 403DFC47258 for ; Tue, 5 May 2020 20:41:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1C57020757 for ; Tue, 5 May 2020 20:41:48 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=chromium.org header.i=@chromium.org header.b="XU6X9GMe" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728853AbgEEUlr (ORCPT ); Tue, 5 May 2020 16:41:47 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53156 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1726350AbgEEUlq (ORCPT ); Tue, 5 May 2020 16:41:46 -0400 Received: from mail-pf1-x442.google.com (mail-pf1-x442.google.com [IPv6:2607:f8b0:4864:20::442]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C1A41C061A10 for ; Tue, 5 May 2020 13:41:46 -0700 (PDT) Received: by mail-pf1-x442.google.com with SMTP id f7so1479085pfa.9 for ; Tue, 05 May 2020 13:41:46 -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=TBeTodJwY1sbypPr0O4/M7Oc5AId4qrDzBRpp3D+bWw=; b=XU6X9GMe8j4wKq96hvrcdX1ByQHmmyBW7U6O/ETyAHaaOeuNGkQLdp5aHsi+ZYAg/n ToTVv9P6DfvsQWmACbq/7EkvxkgQBisVFC+Cuteh8eSBPa0l95XCST9S/53ATidKpelR BE5pJ6fNUlqYODQ8vfoK3eOaI1hndoAxJQXJc= 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=TBeTodJwY1sbypPr0O4/M7Oc5AId4qrDzBRpp3D+bWw=; b=Uw9a4yQwmtez6/qxANGla1rC+xQl8WEHmfkK3pND+C2XLQPnKjxyj1ZrFi6QxwhkMe k/6s3WQ/x+l0Z8GEKF5vKlCXtwYKg+r1SIvoRrTbtB0WMdZcMldLhcsxK3NelxhjvZdT rIKk+l5Se/DBNrKZD8CyJGOoFmRb5BfxbtYT1ZxMUW6/b55BWjlACtuXg2qRBV+Orgzu 4YFxw3ynfhAV17PmLQOSG+XXTzQUKiynSPNZZvqFEXEgg0B/w7Rr9s0tVu5DqAD9n5Gv XjePsq2bXxZFdlO87hvLiULVkyaJSDSwcCSYOmFQgRTcOlULixoio0UmuqB8tADmXuhQ FF0w== X-Gm-Message-State: AGi0PuaGlEzM3yzuLbF59bWvJK/cyOiOIqPBigxW+1phgt0JMQm7QIYX YNmNSRoQ1iWSEdnKlAGdF5R9xA== X-Google-Smtp-Source: APiQypKneSUsTTVo+yZKgZiaXfs8Cdo88B6bTaJHGjy6DGrc5Y7iwWPQe9ZysHr3aN4qrrZAuhv8sQ== X-Received: by 2002:a62:d005:: with SMTP id p5mr5183995pfg.156.1588711306249; Tue, 05 May 2020 13:41:46 -0700 (PDT) Received: from www.outflux.net (smtp.outflux.net. [198.145.64.163]) by smtp.gmail.com with ESMTPSA id g16sm2726879pfq.203.2020.05.05.13.41.45 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 05 May 2020 13:41:45 -0700 (PDT) Date: Tue, 5 May 2020 13:41:44 -0700 From: Kees Cook To: Greg KH Cc: Luis Chamberlain , Christoph Hellwig , Iurii Zaikin , Alexey Dobriyan , linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] sysctl: Make sure proc handlers can't expose heap memory Message-ID: <202005051339.5F1979C4DF@keescook> References: <202005041205.C7AF4AF@keescook> <20200504195937.GS11244@42.do-not-panic.com> <202005041329.169799C65D@keescook> <20200504215903.GT11244@42.do-not-panic.com> <20200505063441.GA3877399@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200505063441.GA3877399@kroah.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, May 05, 2020 at 08:34:41AM +0200, Greg KH wrote: > On Mon, May 04, 2020 at 09:59:03PM +0000, Luis Chamberlain wrote: > > On Mon, May 04, 2020 at 01:32:07PM -0700, Kees Cook wrote: > > > On Mon, May 04, 2020 at 07:59:37PM +0000, Luis Chamberlain wrote: > > > > On Mon, May 04, 2020 at 12:08:55PM -0700, Kees Cook wrote: > > > > > Just as a precaution, make sure that proc handlers don't accidentally > > > > > grow "count" beyond the allocated kbuf size. > > > > > > > > > > Signed-off-by: Kees Cook > > > > > --- > > > > > This applies to hch's sysctl cleanup tree... > > > > > --- > > > > > fs/proc/proc_sysctl.c | 3 +++ > > > > > 1 file changed, 3 insertions(+) > > > > > > > > > > diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c > > > > > index 15030784566c..535ab26473af 100644 > > > > > --- a/fs/proc/proc_sysctl.c > > > > > +++ b/fs/proc/proc_sysctl.c > > > > > @@ -546,6 +546,7 @@ static ssize_t proc_sys_call_handler(struct file *filp, void __user *ubuf, > > > > > struct inode *inode = file_inode(filp); > > > > > struct ctl_table_header *head = grab_header(inode); > > > > > struct ctl_table *table = PROC_I(inode)->sysctl_entry; > > > > > + size_t count_max = count; > > > > > void *kbuf; > > > > > ssize_t error; > > > > > > > > > > @@ -590,6 +591,8 @@ static ssize_t proc_sys_call_handler(struct file *filp, void __user *ubuf, > > > > > > > > > > if (!write) { > > > > > error = -EFAULT; > > > > > + if (WARN_ON(count > count_max)) > > > > > + count = count_max; > > > > > > > > That would crash a system with panic-on-warn. I don't think we want that? > > > > > > Eh? None of the handlers should be making this mistake currently and > > > it's not a mistake that can be controlled from userspace. WARN() is > > > absolutely what's wanted here: report an impossible situation (and > > > handle it gracefully for the bulk of users that don't have > > > panic_on_warn set). > > > > Alrighty, Greg are you OK with this type of WARN_ON()? You recently > > expressed concerns over its use due to panic-on-warn on another patch. > > We should never call WARN() on any path that a user can trigger. > > If it is just a "the developer called this api in a foolish way" then we > could use a WARN_ON() to have them realize their mistake, but in my > personal experience, foolish developers don't even notice that kind of > mistake :( Right -- while it'd be nice if the developer noticed it, it is _usually_ an unsuspecting end user (or fuzzer), in which case we absolutely want a WARN (and not a BUG![1]) and have the situations handled gracefully, so it can be reported and fixed. -Kees [1] https://www.kernel.org/doc/html/latest/process/deprecated.html#bug-and-bug-on -- Kees Cook