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=-14.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_GIT autolearn=unavailable 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 B6BEBC2D0A3 for ; Mon, 9 Nov 2020 13:10:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6F5B520663 for ; Mon, 9 Nov 2020 13:10:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1604927434; bh=FrGFnYVtKu4a5On7eAOPWzNYFNNKSIQ2Y5MlWzgAYCs=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=tkppHpAzgF+SY3hx8k8BIVg4m/2YrNrZyC3+QHsMYg7GNwmXaw3Sqh+dgn6EP74bj uDkdS5eZL9zzSad1frdkYRGsGFXfVgC4za5VSHyYP6A1phasHvCOocP7uDgowQk1FD PdQzm1J4CxzTe/+Z3bpkBw4rcsBKaKhcVecmKg7E= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732098AbgKINKd (ORCPT ); Mon, 9 Nov 2020 08:10:33 -0500 Received: from mail.kernel.org ([198.145.29.99]:35714 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731261AbgKINK2 (ORCPT ); Mon, 9 Nov 2020 08:10:28 -0500 Received: from localhost (83-86-74-64.cable.dynamic.v4.ziggo.nl [83.86.74.64]) (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 3634320663; Mon, 9 Nov 2020 13:10:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1604927426; bh=FrGFnYVtKu4a5On7eAOPWzNYFNNKSIQ2Y5MlWzgAYCs=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=qS78Wdme28T4DhXJLvzgWnbSqnOoCT0q97rCv3hARUUv0Z8wAarS5XRufsZWt6Zt3 rzWn3WDmUmGIJPWfv48pzBGSyIQU2Ji+U66xnfhFEHULzhPLS3iiTISlqwwUJk47CH 6okEX1Bq98Yl73a+zNJvh2IDGAWe9Mf1FeVfF2DY= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Peilin Ye , Minh Yuan , Greg KH , Tetsuo Handa , Daniel Vetter Subject: [PATCH 4.19 55/71] vt: Disable KD_FONT_OP_COPY Date: Mon, 9 Nov 2020 13:55:49 +0100 Message-Id: <20201109125022.487432418@linuxfoundation.org> X-Mailer: git-send-email 2.29.2 In-Reply-To: <20201109125019.906191744@linuxfoundation.org> References: <20201109125019.906191744@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Daniel Vetter commit 3c4e0dff2095c579b142d5a0693257f1c58b4804 upstream. It's buggy: On Fri, Nov 06, 2020 at 10:30:08PM +0800, Minh Yuan wrote: > We recently discovered a slab-out-of-bounds read in fbcon in the latest > kernel ( v5.10-rc2 for now ). The root cause of this vulnerability is that > "fbcon_do_set_font" did not handle "vc->vc_font.data" and > "vc->vc_font.height" correctly, and the patch > for VT_RESIZEX can't handle this > issue. > > Specifically, we use KD_FONT_OP_SET to set a small font.data for tty6, and > use KD_FONT_OP_SET again to set a large font.height for tty1. After that, > we use KD_FONT_OP_COPY to assign tty6's vc_font.data to tty1's vc_font.data > in "fbcon_do_set_font", while tty1 retains the original larger > height. Obviously, this will cause an out-of-bounds read, because we can > access a smaller vc_font.data with a larger vc_font.height. Further there was only one user ever. - Android's loadfont, busybox and console-tools only ever use OP_GET and OP_SET - fbset documentation only mentions the kernel cmdline font: option, not anything else. - systemd used OP_COPY before release 232 published in Nov 2016 Now unfortunately the crucial report seems to have gone down with gmane, and the commit message doesn't say much. But the pull request hints at OP_COPY being broken https://github.com/systemd/systemd/pull/3651 So in other words, this never worked, and the only project which foolishly every tried to use it, realized that rather quickly too. Instead of trying to fix security issues here on dead code by adding missing checks, fix the entire thing by removing the functionality. Note that systemd code using the OP_COPY function ignored the return value, so it doesn't matter what we're doing here really - just in case a lone server somewhere happens to be extremely unlucky and running an affected old version of systemd. The relevant code from font_copy_to_all_vcs() in systemd was: /* copy font from active VT, where the font was uploaded to */ cfo.op = KD_FONT_OP_COPY; cfo.height = vcs.v_active-1; /* tty1 == index 0 */ (void) ioctl(vcfd, KDFONTOP, &cfo); Note this just disables the ioctl, garbage collecting the now unused callbacks is left for -next. v2: Tetsuo found the old mail, which allowed me to find it on another archive. Add the link too. Acked-by: Peilin Ye Reported-by: Minh Yuan Cc: Greg KH Cc: Peilin Ye Cc: Tetsuo Handa Signed-off-by: Daniel Vetter Link: https://lore.kernel.org/r/20201108153806.3140315-1-daniel.vetter@ffwll.ch Signed-off-by: Greg Kroah-Hartman --- drivers/tty/vt/vt.c | 24 ++---------------------- 1 file changed, 2 insertions(+), 22 deletions(-) --- a/drivers/tty/vt/vt.c +++ b/drivers/tty/vt/vt.c @@ -4574,27 +4574,6 @@ static int con_font_default(struct vc_da return rc; } -static int con_font_copy(struct vc_data *vc, struct console_font_op *op) -{ - int con = op->height; - int rc; - - - console_lock(); - if (vc->vc_mode != KD_TEXT) - rc = -EINVAL; - else if (!vc->vc_sw->con_font_copy) - rc = -ENOSYS; - else if (con < 0 || !vc_cons_allocated(con)) - rc = -ENOTTY; - else if (con == vc->vc_num) /* nothing to do */ - rc = 0; - else - rc = vc->vc_sw->con_font_copy(vc, con); - console_unlock(); - return rc; -} - int con_font_op(struct vc_data *vc, struct console_font_op *op) { switch (op->op) { @@ -4605,7 +4584,8 @@ int con_font_op(struct vc_data *vc, stru case KD_FONT_OP_SET_DEFAULT: return con_font_default(vc, op); case KD_FONT_OP_COPY: - return con_font_copy(vc, op); + /* was buggy and never really used */ + return -EINVAL; } return -ENOSYS; }