Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753548AbcKSJWB (ORCPT ); Sat, 19 Nov 2016 04:22:01 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:58010 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753478AbcKSJVy (ORCPT ); Sat, 19 Nov 2016 04:21:54 -0500 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Tilman Schmidt , Sasha Levin , Peter Hurley , Jiri Slaby Subject: [PATCH 4.4 17/37] tty: Prevent ldisc drivers from re-using stale tty fields Date: Sat, 19 Nov 2016 10:20:33 +0100 Message-Id: <20161119092010.903294328@linuxfoundation.org> X-Mailer: git-send-email 2.10.2 In-Reply-To: <20161119092010.016555184@linuxfoundation.org> References: <20161119092010.016555184@linuxfoundation.org> User-Agent: quilt/0.65 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3126 Lines: 79 4.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Peter Hurley commit dd42bf1197144ede075a9d4793123f7689e164bc upstream. Line discipline drivers may mistakenly misuse ldisc-related fields when initializing. For example, a failure to initialize tty->receive_room in the N_GIGASET_M101 line discipline was recently found and fixed [1]. Now, the N_X25 line discipline has been discovered accessing the previous line discipline's already-freed private data [2]. Harden the ldisc interface against misuse by initializing revelant tty fields before instancing the new line discipline. [1] commit fd98e9419d8d622a4de91f76b306af6aa627aa9c Author: Tilman Schmidt Date: Tue Jul 14 00:37:13 2015 +0200 isdn/gigaset: reset tty->receive_room when attaching ser_gigaset [2] Report from Sasha Levin [ 634.336761] ================================================================== [ 634.338226] BUG: KASAN: use-after-free in x25_asy_open_tty+0x13d/0x490 at addr ffff8800a743efd0 [ 634.339558] Read of size 4 by task syzkaller_execu/8981 [ 634.340359] ============================================================================= [ 634.341598] BUG kmalloc-512 (Not tainted): kasan: bad access detected ... [ 634.405018] Call Trace: [ 634.405277] dump_stack (lib/dump_stack.c:52) [ 634.405775] print_trailer (mm/slub.c:655) [ 634.406361] object_err (mm/slub.c:662) [ 634.406824] kasan_report_error (mm/kasan/report.c:138 mm/kasan/report.c:236) [ 634.409581] __asan_report_load4_noabort (mm/kasan/report.c:279) [ 634.411355] x25_asy_open_tty (drivers/net/wan/x25_asy.c:559 (discriminator 1)) [ 634.413997] tty_ldisc_open.isra.2 (drivers/tty/tty_ldisc.c:447) [ 634.414549] tty_set_ldisc (drivers/tty/tty_ldisc.c:567) [ 634.415057] tty_ioctl (drivers/tty/tty_io.c:2646 drivers/tty/tty_io.c:2879) [ 634.423524] do_vfs_ioctl (fs/ioctl.c:43 fs/ioctl.c:607) [ 634.427491] SyS_ioctl (fs/ioctl.c:622 fs/ioctl.c:613) [ 634.427945] entry_SYSCALL_64_fastpath (arch/x86/entry/entry_64.S:188) Cc: Tilman Schmidt Cc: Sasha Levin Signed-off-by: Peter Hurley Cc: Jiri Slaby Signed-off-by: Greg Kroah-Hartman --- drivers/tty/tty_ldisc.c | 7 +++++++ 1 file changed, 7 insertions(+) --- a/drivers/tty/tty_ldisc.c +++ b/drivers/tty/tty_ldisc.c @@ -417,6 +417,10 @@ EXPORT_SYMBOL_GPL(tty_ldisc_flush); * they are not on hot paths so a little discipline won't do * any harm. * + * The line discipline-related tty_struct fields are reset to + * prevent the ldisc driver from re-using stale information for + * the new ldisc instance. + * * Locking: takes termios_rwsem */ @@ -425,6 +429,9 @@ static void tty_set_termios_ldisc(struct down_write(&tty->termios_rwsem); tty->termios.c_line = num; up_write(&tty->termios_rwsem); + + tty->disc_data = NULL; + tty->receive_room = 0; } /**