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=-4.0 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, 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 29F71C54E8E for ; Tue, 12 May 2020 14:49:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 03E1120736 for ; Tue, 12 May 2020 14:49:19 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="TEP/hivc" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727982AbgELOtS (ORCPT ); Tue, 12 May 2020 10:49:18 -0400 Received: from us-smtp-2.mimecast.com ([205.139.110.61]:30192 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727100AbgELOtR (ORCPT ); Tue, 12 May 2020 10:49:17 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1589294956; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=jx+puuCmllp6pyXQNaubWo+qtrpR0nODcwxMTtKrcSI=; b=TEP/hivcoxT+LrYt8ru6wCChWSNSqJu8gNtaf3R1foIQH/lDp156xulyk3FYI/Qj3Gz8mK gkDyAKQr7G6WCBrpmFC1yzK6tIfEdZLHFX+aF1wPLW9jiVAR2KZqsMM+Lo7Y0byx4Ds8O7 OZjsTEHe2OQtzqe2/T+IXoa5FWoWN8s= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-4-Mfu0zy3TOOmWSoFOm3Tffw-1; Tue, 12 May 2020 10:49:12 -0400 X-MC-Unique: Mfu0zy3TOOmWSoFOm3Tffw-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 4FEAC100A614; Tue, 12 May 2020 14:49:11 +0000 (UTC) Received: from optiplex-lnx (unknown [10.3.128.26]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 99BB462A28; Tue, 12 May 2020 14:49:09 +0000 (UTC) Date: Tue, 12 May 2020 10:49:06 -0400 From: Rafael Aquini To: Luis Chamberlain Cc: Tso Ted , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, keescook@chromium.org, yzaikin@google.com Subject: Re: [PATCH] kernel: sysctl: ignore invalid taint bits introduced via kernel.tainted and taint the kernel with TAINT_USER on writes Message-ID: <20200512144906.GG367616@optiplex-lnx> References: <20200511215904.719257-1-aquini@redhat.com> <20200511231045.GV11244@42.do-not-panic.com> <20200511235914.GF367616@optiplex-lnx> <20200512001702.GW11244@42.do-not-panic.com> <20200512010313.GA725253@optiplex-lnx> <20200512050405.GY11244@42.do-not-panic.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20200512050405.GY11244@42.do-not-panic.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, May 12, 2020 at 05:04:05AM +0000, Luis Chamberlain wrote: > On Mon, May 11, 2020 at 09:03:13PM -0400, Rafael Aquini wrote: > > On Tue, May 12, 2020 at 12:17:03AM +0000, Luis Chamberlain wrote: > > > On Mon, May 11, 2020 at 07:59:14PM -0400, Rafael Aquini wrote: > > > > On Mon, May 11, 2020 at 11:10:45PM +0000, Luis Chamberlain wrote: > > > > > On Mon, May 11, 2020 at 05:59:04PM -0400, Rafael Aquini wrote: > > > > > > diff --git a/kernel/sysctl.c b/kernel/sysctl.c > > > > > > index 8a176d8727a3..f0a4fb38ac62 100644 > > > > > > --- a/kernel/sysctl.c > > > > > > +++ b/kernel/sysctl.c > > > > > > @@ -2623,17 +2623,32 @@ static int proc_taint(struct ctl_table *table, int write, > > > > > > return err; > > > > > > > > > > > > if (write) { > > > > > > + int i; > > > > > > + > > > > > > + /* > > > > > > + * Ignore user input that would make us committing > > > > > > + * arbitrary invalid TAINT flags in the loop below. > > > > > > + */ > > > > > > + tmptaint &= (1UL << TAINT_FLAGS_COUNT) - 1; > > > > > > > > > > This looks good but we don't pr_warn() of information lost on intention. > > > > > > > > > > > > > Are you thinking in sth like: > > > > > > > > + if (tmptaint > TAINT_FLAGS_MAX) { > > > > + tmptaint &= TAINT_FLAGS_MAX; > > > > + pr_warn("proc_taint: out-of-range invalid input ignored" > > > > + " tainted_mask adjusted to 0x%x\n", tmptaint); > > > > + } > > > > ? > > > > > > Sure that would clarify this. > > > > > > > > > + > > > > > > /* > > > > > > * Poor man's atomic or. Not worth adding a primitive > > > > > > * to everyone's atomic.h for this > > > > > > */ > > > > > > - int i; > > > > > > for (i = 0; i < BITS_PER_LONG && tmptaint >> i; i++) { > > > > > > if ((tmptaint >> i) & 1) > > > > > > add_taint(i, LOCKDEP_STILL_OK); > > > > > > } > > > > > > + > > > > > > + /* > > > > > > + * Users with SYS_ADMIN capability can include any arbitrary > > > > > > + * taint flag by writing to this interface. If that's the case, > > > > > > + * we also need to mark the kernel "tainted by user". > > > > > > + */ > > > > > > + add_taint(TAINT_USER, LOCKDEP_STILL_OK); > > > > > > > > > > I'm in favor of this however I'd like to hear from Ted on if it meets > > > > > the original intention. I would think he had a good reason not to add > > > > > it here. > > > > > > > > > > > > > Fair enough. The impression I got by reading Ted's original commit > > > > message is that the intent was to have TAINT_USER as the flag set > > > > via this interface, even though the code was allowing for any > > > > arbitrary value. > > > > > > That wasn't my reading, it was that the user did something very odd > > > with user input which we don't like as kernel developers, and it gives > > > us a way to prove: hey you did something stupid, sorry but I cannot > > > support your kernel panic. > > > > > > > I think it's OK to let the user fiddle with > > > > the flags, as it's been allowed since the introduction of > > > > this interface, but we need to reflect that fact in the > > > > tainting itself. Since TAINT_USER is not used anywhere, > > > > > > I see users of TAINT_USER sprinkled around > > > > > > > I meant in the original commit that introduced it > > (commit 34f5a39899f3f3e815da64f48ddb72942d86c366). Sorry I > > miscomunicated that. > > > > In its current usage, it seems that the other places adding TAINT_USER > > match with what is being proposed here: To signal when we have user > > fiddling with kernel / module parameters. > > drivers/base/regmap/regmap-debugfs.c requires *manual* code changes > to compile / enable some knob. i915 complains about unsafe module > params such as module_param_cb_unsafe() core_param_unsafe(). Then > drivers/soundwire/cadence_master.c is for when a debugfs dangerous > param was used. > > This still doesn't rule out the use of proc_taint() for testing taint, > and that adding it may break some tests. So even though this would > only affect some tests scripts, I can't say that adding this taint won't > cause some headaches to someone. I wouldn't encourage its use on > proc_taint() from what I can see so far. > OK, IŽll repost without the hunk forcing the taint. If we eventually come to the conclusion that tainting in proc_taint() is the right thing to do, we can do that part of the change later. Do you think we should use printk_ratelimited() in the ignore message, instead? Cheers, -- Rafael