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=-4.5 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FSL_HELO_FAKE,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 9F351C3F2CD for ; Mon, 2 Mar 2020 21:23:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6C4F82465D for ; Mon, 2 Mar 2020 21:23:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1583184190; bh=TJupXr/A9HuRmVFgG+U+VpwxHs2hBti9AoPK9ebZUzs=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=AOmaMcy/WxXtGfXROEZ+vXWZSJWRIh1dwwmM6UHZ+8uEGIqCbsBLlH0BaDWAiNtBS 5pGJNFdjLkHU2YJMgi2NE75y9Yqq3r2od8/t1jaVqp+Rf00ydKUrF5efTYSe7ctw7G 7wZnljkIyuvmC8xgALtFWIXTcHyD5f1eg/oXFdAE= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726793AbgCBVXJ (ORCPT ); Mon, 2 Mar 2020 16:23:09 -0500 Received: from mail.kernel.org ([198.145.29.99]:53788 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726695AbgCBVXJ (ORCPT ); Mon, 2 Mar 2020 16:23:09 -0500 Received: from gmail.com (unknown [104.132.1.77]) (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 1F812208C3; Mon, 2 Mar 2020 21:23:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1583184188; bh=TJupXr/A9HuRmVFgG+U+VpwxHs2hBti9AoPK9ebZUzs=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=vpw6iZVEpj+hrQnQps894lQiOuiaovukJTkjoE6UleQvgl+paymvY9HDB+gt0KZqR mpAXsQLV6lMZnV6nwsTo1bz3Zo/bYJP7df9DHYb/a870op8rH+MOdluz8GMpTYt+4C Bwmmu0hDhemion6XKFQmaW9hnfJSauUlvsvB7SXg= Date: Mon, 2 Mar 2020 13:23:06 -0800 From: Eric Biggers To: Jiri Slaby Cc: Greg Kroah-Hartman , linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com, Eric Dumazet , Nicolas Pitre , Alan Cox Subject: Re: [PATCH] vt: vt_ioctl: fix VT_DISALLOCATE freeing in-use virtual console Message-ID: <20200302212306.GA78660@gmail.com> References: <0000000000006663de0598d25ab1@google.com> <20200224071247.283098-1-ebiggers@kernel.org> <8fb00b38-abd0-6895-3ad2-85a6f05ee6cf@suse.com> <20200224081913.GA299238@sol.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200224081913.GA299238@sol.localdomain> User-Agent: Mutt/1.12.2 (2019-09-21) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Feb 24, 2020 at 12:19:13AM -0800, Eric Biggers wrote: > On Mon, Feb 24, 2020 at 09:04:33AM +0100, Jiri Slaby wrote: > > > KASAN report: > > > BUG: KASAN: use-after-free in con_shutdown+0x76/0x80 drivers/tty/vt/vt.c:3278 > > > Write of size 8 at addr ffff88806a4ec108 by task syz_vt/129 > > > > > > CPU: 0 PID: 129 Comm: syz_vt Not tainted 5.6.0-rc2 #11 > > > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS ?-20191223_100556-anatol 04/01/2014 > > > Call Trace: > > > [...] > > > con_shutdown+0x76/0x80 drivers/tty/vt/vt.c:3278 > > > release_tty+0xa8/0x410 drivers/tty/tty_io.c:1514 > > > tty_release_struct+0x34/0x50 drivers/tty/tty_io.c:1629 > > > tty_release+0x984/0xed0 drivers/tty/tty_io.c:1789 > > > [...] > > > > > > Allocated by task 129: > > > [...] > > > kzalloc include/linux/slab.h:669 [inline] > > > vc_allocate drivers/tty/vt/vt.c:1085 [inline] > > > vc_allocate+0x1ac/0x680 drivers/tty/vt/vt.c:1066 > > > con_install+0x4d/0x3f0 drivers/tty/vt/vt.c:3229 > > > tty_driver_install_tty drivers/tty/tty_io.c:1228 [inline] > > > tty_init_dev+0x94/0x350 drivers/tty/tty_io.c:1341 > > > tty_open_by_driver drivers/tty/tty_io.c:1987 [inline] > > > tty_open+0x3ca/0xb30 drivers/tty/tty_io.c:2035 > > > [...] > > > > > > Freed by task 130: > > > [...] > > > kfree+0xbf/0x1e0 mm/slab.c:3757 > > > vt_disallocate drivers/tty/vt/vt_ioctl.c:300 [inline] > > > vt_ioctl+0x16dc/0x1e30 drivers/tty/vt/vt_ioctl.c:818 > > > tty_ioctl+0x9db/0x11b0 drivers/tty/tty_io.c:2660 > > > > That means the associated tty_port is destroyed while the tty layer > > still has a tty on the top of it. That is a BUG anyway. > > > > > Fixes: 4001d7b7fc27 ("vt: push down the tty lock so we can see what is left to tackle") > > > Cc: # v3.4+ > > > Reported-by: syzbot+522643ab5729b0421998@syzkaller.appspotmail.com > > > Signed-off-by: Eric Biggers > > > --- > > > drivers/tty/vt/vt_ioctl.c | 6 +++++- > > > 1 file changed, 5 insertions(+), 1 deletion(-) > > > > > > diff --git a/drivers/tty/vt/vt_ioctl.c b/drivers/tty/vt/vt_ioctl.c > > > index ee6c91ef1f6cf..57d681706fa85 100644 > > > --- a/drivers/tty/vt/vt_ioctl.c > > > +++ b/drivers/tty/vt/vt_ioctl.c > > > @@ -42,7 +42,7 @@ > > > char vt_dont_switch; > > > extern struct tty_driver *console_driver; > > > > > > -#define VT_IS_IN_USE(i) (console_driver->ttys[i] && console_driver->ttys[i]->count) > > > +#define VT_IS_IN_USE(i) (console_driver->ttys[i] != NULL) > > > #define VT_BUSY(i) (VT_IS_IN_USE(i) || i == fg_console || vc_cons[i].d == sel_cons) > > > > > > /* > > > @@ -288,12 +288,14 @@ static int vt_disallocate(unsigned int vc_num) > > > struct vc_data *vc = NULL; > > > int ret = 0; > > > > > > + mutex_lock(&tty_mutex); /* synchronize with release_tty() */ > > > console_lock(); > > > > Is this lock dependency new or pre-existing? > > It's the same locking order used during release_tty(). > > > > > Locking tty_mutex here does not sound quite right. What about switching > > vc_data to proper refcounting based on tty_port? (Instead of doing > > tty_port_destroy and kfree in vt_disallocate*.) > > > > How would that work? We could make struct vc_data refcounted such that > VT_DISALLOCATE doesn't free it right away but rather it's freed in the next > con_shutdown(). But release_tty() still accesses tty->port afterwards, which is > part of the 'struct vc_data' that would have just been freed. > Jiri, can you explain what you meant here? I don't see how your suggestion would solve the problem. Greg, any opinion? - Eric