From patchwork Wed Apr 1 16:18:24 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Greg Kroah-Hartman X-Patchwork-Id: 228453 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, HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI, 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 F08E0C2D0F0 for ; Wed, 1 Apr 2020 16:34:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8F58C21582 for ; Wed, 1 Apr 2020 16:34:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1585758843; bh=hr+cRpCOqgX4KW48mwt0QGF1Hv9qMVptSISNfFGD2KA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=qATVAQYz2ubaMXSSRs7lKc7Lkj8oDA8lph6D2d1Wj1xt2z2h3FJ4DVsjA8FWdH02r o7FM43aln0HG6Wb+/ZvD95tR5t2fekt7y7vtfxG6P9CJCK+nKRiirjXKFlVFOGE4rw zLq6Wie5pdT+3wI0Y42wjr2fQbAboELAihI1vPMg= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388597AbgDAQdt (ORCPT ); Wed, 1 Apr 2020 12:33:49 -0400 Received: from mail.kernel.org ([198.145.29.99]:60400 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388595AbgDAQds (ORCPT ); Wed, 1 Apr 2020 12:33:48 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (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 ADF21212CC; Wed, 1 Apr 2020 16:33:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1585758828; bh=hr+cRpCOqgX4KW48mwt0QGF1Hv9qMVptSISNfFGD2KA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=rC5bGe1jyC/O3rByTx/6XPuojb3ZdwHr90bDkhewPntveOD9graz03Jo9G72nnTlk soJvSOkWhoQVdY5aqZ7RdPnUFa7JooqwkqaRfjurz9bRD64jaKFb6yoPzCLi6f7OZq 5Xu7KxjEqIVYnCNekLbq2cy/d0CupWy17nwO8H3E= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Jiri Slaby , Eric Biggers Subject: [PATCH 4.4 88/91] vt: vt_ioctl: fix use-after-free in vt_in_use() Date: Wed, 1 Apr 2020 18:18:24 +0200 Message-Id: <20200401161539.968827302@linuxfoundation.org> X-Mailer: git-send-email 2.26.0 In-Reply-To: <20200401161512.917494101@linuxfoundation.org> References: <20200401161512.917494101@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Eric Biggers commit 7cf64b18b0b96e751178b8d0505d8466ff5a448f upstream. vt_in_use() dereferences console_driver->ttys[i] without proper locking. This is broken because the tty can be closed and freed concurrently. We could fix this by using 'READ_ONCE(console_driver->ttys[i]) != NULL' and skipping the check of tty_struct::count. But, looking at console_driver->ttys[i] isn't really appropriate anyway because even if it is NULL the tty can still be in the process of being closed. Instead, fix it by making vt_in_use() require console_lock() and check whether the vt is allocated and has port refcount > 1. This works since following the patch "vt: vt_ioctl: fix VT_DISALLOCATE freeing in-use virtual console" the port refcount is incremented while the vt is open. Reproducer (very unreliable, but it worked for me after a few minutes): #include #include int main() { int fd, nproc; struct vt_stat state; char ttyname[16]; fd = open("/dev/tty10", O_RDONLY); for (nproc = 1; nproc < 8; nproc *= 2) fork(); for (;;) { sprintf(ttyname, "/dev/tty%d", rand() % 8); close(open(ttyname, O_RDONLY)); ioctl(fd, VT_GETSTATE, &state); } } KASAN report: BUG: KASAN: use-after-free in vt_in_use drivers/tty/vt/vt_ioctl.c:48 [inline] BUG: KASAN: use-after-free in vt_ioctl+0x1ad3/0x1d70 drivers/tty/vt/vt_ioctl.c:657 Read of size 4 at addr ffff888065722468 by task syz-vt2/132 CPU: 0 PID: 132 Comm: syz-vt2 Not tainted 5.6.0-rc5-00130-g089b6d3654916 #13 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS ?-20191223_100556-anatol 04/01/2014 Call Trace: [...] vt_in_use drivers/tty/vt/vt_ioctl.c:48 [inline] vt_ioctl+0x1ad3/0x1d70 drivers/tty/vt/vt_ioctl.c:657 tty_ioctl+0x9db/0x11b0 drivers/tty/tty_io.c:2660 [...] Allocated by task 136: [...] kzalloc include/linux/slab.h:669 [inline] alloc_tty_struct+0x96/0x8a0 drivers/tty/tty_io.c:2982 tty_init_dev+0x23/0x350 drivers/tty/tty_io.c:1334 tty_open_by_driver drivers/tty/tty_io.c:1987 [inline] tty_open+0x3ca/0xb30 drivers/tty/tty_io.c:2035 [...] Freed by task 41: [...] kfree+0xbf/0x200 mm/slab.c:3757 free_tty_struct+0x8d/0xb0 drivers/tty/tty_io.c:177 release_one_tty+0x22d/0x2f0 drivers/tty/tty_io.c:1468 process_one_work+0x7f1/0x14b0 kernel/workqueue.c:2264 worker_thread+0x8b/0xc80 kernel/workqueue.c:2410 [...] Fixes: 4001d7b7fc27 ("vt: push down the tty lock so we can see what is left to tackle") Cc: # v3.4+ Acked-by: Jiri Slaby Signed-off-by: Eric Biggers Link: https://lore.kernel.org/r/20200322034305.210082-3-ebiggers@kernel.org Signed-off-by: Greg Kroah-Hartman --- drivers/tty/vt/vt_ioctl.c | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-) --- a/drivers/tty/vt/vt_ioctl.c +++ b/drivers/tty/vt/vt_ioctl.c @@ -42,9 +42,15 @@ bool vt_dont_switch; static inline bool vt_in_use(unsigned int i) { - extern struct tty_driver *console_driver; + const struct vc_data *vc = vc_cons[i].d; - return console_driver->ttys[i] && console_driver->ttys[i]->count; + /* + * console_lock must be held to prevent the vc from being deallocated + * while we're checking whether it's in-use. + */ + WARN_CONSOLE_UNLOCKED(); + + return vc && kref_read(&vc->port.kref) > 1; } static inline bool vt_busy(int i) @@ -646,15 +652,16 @@ int vt_ioctl(struct tty_struct *tty, struct vt_stat __user *vtstat = up; unsigned short state, mask; - /* Review: FIXME: Console lock ? */ if (put_user(fg_console + 1, &vtstat->v_active)) ret = -EFAULT; else { state = 1; /* /dev/tty0 is always open */ + console_lock(); /* required by vt_in_use() */ for (i = 0, mask = 2; i < MAX_NR_CONSOLES && mask; ++i, mask <<= 1) if (vt_in_use(i)) state |= mask; + console_unlock(); ret = put_user(state, &vtstat->v_state); } break; @@ -664,10 +671,11 @@ int vt_ioctl(struct tty_struct *tty, * Returns the first available (non-opened) console. */ case VT_OPENQRY: - /* FIXME: locking ? - but then this is a stupid API */ + console_lock(); /* required by vt_in_use() */ for (i = 0; i < MAX_NR_CONSOLES; ++i) if (!vt_in_use(i)) break; + console_unlock(); uival = i < MAX_NR_CONSOLES ? (i+1) : -1; goto setint;