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=-10.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT 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 E3063C43333 for ; Sun, 22 Mar 2020 03:44:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id AEB7920739 for ; Sun, 22 Mar 2020 03:44:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1584848670; bh=+19Z5Tye1PAVVFfmfRIwC11NhXs130KCz5NNO25vAd4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=lKzYgGoSiKOkbYp2+LiMko+13UcfYWPNd4i15GtuJmxE+5/OStEqOQ+tg/UQ7ItJ5 Y7N2y167NXJoNKCme2QU3XQLX/v0Rbab9bkdipEuuo8rgeOQcKgT2mj5Kp33+VYoZQ /ORBukpWbj/f3MFOo45EaR90sw1Q8TfBuE/Qm530= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728315AbgCVDo3 (ORCPT ); Sat, 21 Mar 2020 23:44:29 -0400 Received: from mail.kernel.org ([198.145.29.99]:49936 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727916AbgCVDo3 (ORCPT ); Sat, 21 Mar 2020 23:44:29 -0400 Received: from sol.hsd1.ca.comcast.net (c-107-3-166-239.hsd1.ca.comcast.net [107.3.166.239]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 82D7B20719; Sun, 22 Mar 2020 03:44:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1584848668; bh=+19Z5Tye1PAVVFfmfRIwC11NhXs130KCz5NNO25vAd4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=n+JCO1WHdA8wlOv1RWpGRU+eIEjaWP9HWjzrFaTow9dijQCgIjlmzSINrDFFSxMCr s9VleGzkWGzSbP+tLdp0+KgaMdQHAxbQcMW80Iy8yX5EeTqUHR9Sxf1QjzJ9tK2Kw+ 3jUV8B2WShWLZS2iozxWnXQRiney8kPK9zUhdsMs= From: Eric Biggers To: Greg Kroah-Hartman , Jiri Slaby Cc: linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org, syzkaller-bugs@googlegroups.com, Eric Dumazet , Nicolas Pitre Subject: [PATCH v3 1/2] vt: vt_ioctl: fix VT_DISALLOCATE freeing in-use virtual console Date: Sat, 21 Mar 2020 20:43:04 -0700 Message-Id: <20200322034305.210082-2-ebiggers@kernel.org> X-Mailer: git-send-email 2.25.2 In-Reply-To: <20200322034305.210082-1-ebiggers@kernel.org> References: <20200320193424.GM851@sol.localdomain> <20200322034305.210082-1-ebiggers@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Eric Biggers The VT_DISALLOCATE ioctl can free a virtual console while tty_release() is still running, causing a use-after-free in con_shutdown(). This occurs because VT_DISALLOCATE considers a virtual console's 'struct vc_data' to be unused as soon as the corresponding tty's refcount hits 0. But actually it may be still being closed. Fix this by making vc_data be reference-counted via the embedded 'struct tty_port'. A newly allocated virtual console has refcount 1. Opening it for the first time increments the refcount to 2. Closing it for the last time decrements the refcount (in tty_operations::cleanup() so that it happens late enough), as does VT_DISALLOCATE. Reproducer: #include #include #include #include int main() { if (fork()) { for (;;) close(open("/dev/tty5", O_RDWR)); } else { int fd = open("/dev/tty10", O_RDWR); for (;;) ioctl(fd, VT_DISALLOCATE, 5); } } 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 [...] 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.c | 23 ++++++++++++++++++++++- drivers/tty/vt/vt_ioctl.c | 12 ++++-------- 2 files changed, 26 insertions(+), 9 deletions(-) diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c index bbc26d73209a4..309a39197be0a 100644 --- a/drivers/tty/vt/vt.c +++ b/drivers/tty/vt/vt.c @@ -1075,6 +1075,17 @@ static void visual_deinit(struct vc_data *vc) module_put(vc->vc_sw->owner); } +static void vc_port_destruct(struct tty_port *port) +{ + struct vc_data *vc = container_of(port, struct vc_data, port); + + kfree(vc); +} + +static const struct tty_port_operations vc_port_ops = { + .destruct = vc_port_destruct, +}; + int vc_allocate(unsigned int currcons) /* return 0 on success */ { struct vt_notifier_param param; @@ -1100,6 +1111,7 @@ int vc_allocate(unsigned int currcons) /* return 0 on success */ vc_cons[currcons].d = vc; tty_port_init(&vc->port); + vc->port.ops = &vc_port_ops; INIT_WORK(&vc_cons[currcons].SAK_work, vc_SAK); visual_init(vc, currcons, 1); @@ -3250,6 +3262,7 @@ static int con_install(struct tty_driver *driver, struct tty_struct *tty) tty->driver_data = vc; vc->port.tty = tty; + tty_port_get(&vc->port); if (!tty->winsize.ws_row && !tty->winsize.ws_col) { tty->winsize.ws_row = vc_cons[currcons].d->vc_rows; @@ -3285,6 +3298,13 @@ static void con_shutdown(struct tty_struct *tty) console_unlock(); } +static void con_cleanup(struct tty_struct *tty) +{ + struct vc_data *vc = tty->driver_data; + + tty_port_put(&vc->port); +} + static int default_color = 7; /* white */ static int default_italic_color = 2; // green (ASCII) static int default_underline_color = 3; // cyan (ASCII) @@ -3410,7 +3430,8 @@ static const struct tty_operations con_ops = { .throttle = con_throttle, .unthrottle = con_unthrottle, .resize = vt_resize, - .shutdown = con_shutdown + .shutdown = con_shutdown, + .cleanup = con_cleanup, }; static struct cdev vc0_cdev; diff --git a/drivers/tty/vt/vt_ioctl.c b/drivers/tty/vt/vt_ioctl.c index 7297997fcf04c..f62f498f63c05 100644 --- a/drivers/tty/vt/vt_ioctl.c +++ b/drivers/tty/vt/vt_ioctl.c @@ -310,10 +310,8 @@ static int vt_disallocate(unsigned int vc_num) vc = vc_deallocate(vc_num); console_unlock(); - if (vc && vc_num >= MIN_NR_CONSOLES) { - tty_port_destroy(&vc->port); - kfree(vc); - } + if (vc && vc_num >= MIN_NR_CONSOLES) + tty_port_put(&vc->port); return ret; } @@ -333,10 +331,8 @@ static void vt_disallocate_all(void) console_unlock(); for (i = 1; i < MAX_NR_CONSOLES; i++) { - if (vc[i] && i >= MIN_NR_CONSOLES) { - tty_port_destroy(&vc[i]->port); - kfree(vc[i]); - } + if (vc[i] && i >= MIN_NR_CONSOLES) + tty_port_put(&vc[i]->port); } } -- 2.25.2