From patchwork Mon Mar 9 09:51:59 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Anthony Mallet X-Patchwork-Id: 11426511 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id AA60D921 for ; Mon, 9 Mar 2020 09:52:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 90DAF20828 for ; Mon, 9 Mar 2020 09:52:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726368AbgCIJwP (ORCPT ); Mon, 9 Mar 2020 05:52:15 -0400 Received: from laas.laas.fr ([140.93.0.15]:19220 "EHLO laas.laas.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725942AbgCIJwP (ORCPT ); Mon, 9 Mar 2020 05:52:15 -0400 Received: from beetle.laas.fr (beetle.laas.fr [IPv6:2001:660:6602:4:4a4d:7eff:fee1:650a]) by laas.laas.fr (8.16.0.21/8.16.0.29) with SMTP id 0299q8o3033093; Mon, 9 Mar 2020 10:52:08 +0100 (CET) Received: by beetle.laas.fr (sSMTP sendmail emulation); Mon, 09 Mar 2020 10:52:08 +0100 From: Anthony Mallet To: Oliver Neukum , linux-usb@vger.kernel.org Cc: Anthony Mallet Subject: [PATCH 2/2] USB: cdc-acm: fix rounding error in TIOCSSERIAL Date: Mon, 9 Mar 2020 10:51:59 +0100 Message-Id: <20200309095159.14163-2-anthony.mallet@laas.fr> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20200309095159.14163-1-anthony.mallet@laas.fr> References: <20200309095159.14163-1-anthony.mallet@laas.fr> Sender: linux-usb-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-usb@vger.kernel.org Quoting the bug reporter: By default, tty_port_init() initializes those parameters to a multiple of HZ. For instance in line 69 of tty_port.c: port->close_delay = (50 * HZ) / 100; https://github.com/torvalds/linux/blob/master/drivers/tty/tty_port.c#L69 With e.g. CONFIG_HZ = 250 (as this is the case for Ubuntu 18.04 linux-image-4.15.0-37-generic), the default setting for close_delay is thus 125. When ioctl(fd, TIOCGSERIAL, &s) is executed, the setting returned in user space is '12' (125/10). When ioctl(fd, TIOCSSERIAL, &s) is then executed with the same setting '12', the value is interpreted as '120' which is different from the current setting and a EPERM error may be raised by set_serial_info() if !CAP_SYS_ADMIN. https://github.com/torvalds/linux/blob/master/drivers/usb/class/cdc-acm.c#L919 Fixes: ba2d8ce9db0a6 ("cdc-acm: implement TIOCSSERIAL to avoid blocking close(2)") Signed-off-by: Anthony Mallet --- drivers/usb/class/cdc-acm.c | 27 +++++++++++++++++---------- 1 file changed, 17 insertions(+), 10 deletions(-) 2.17.1 diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c index da619176deca..a41a3d27016c 100644 --- a/drivers/usb/class/cdc-acm.c +++ b/drivers/usb/class/cdc-acm.c @@ -907,6 +907,7 @@ static int set_serial_info(struct tty_struct *tty, struct serial_struct *ss) { struct acm *acm = tty->driver_data; unsigned int closing_wait, close_delay; + unsigned int old_closing_wait, old_close_delay; int retval = 0; close_delay = msecs_to_jiffies(ss->close_delay * 10); @@ -914,19 +915,24 @@ static int set_serial_info(struct tty_struct *tty, struct serial_struct *ss) ASYNC_CLOSING_WAIT_NONE : msecs_to_jiffies(ss->closing_wait * 10); + /* we must redo the rounding here, so that the values match */ + old_close_delay = jiffies_to_msecs(acm->port.close_delay) / 10; + old_closing_wait = acm->port.closing_wait == ASYNC_CLOSING_WAIT_NONE ? + ASYNC_CLOSING_WAIT_NONE : + jiffies_to_msecs(acm->port.closing_wait) / 10; + mutex_lock(&acm->port.mutex); - if (!capable(CAP_SYS_ADMIN)) { - if ((close_delay != acm->port.close_delay) || - (closing_wait != acm->port.closing_wait)) + if ((ss->close_delay != old_close_delay) || + (ss->closing_wait != old_closing_wait)) { + if (!capable(CAP_SYS_ADMIN)) retval = -EPERM; - else - retval = -EOPNOTSUPP; - } else { - acm->port.close_delay = close_delay; - acm->port.closing_wait = closing_wait; - } + else { + acm->port.close_delay = close_delay; + acm->port.closing_wait = closing_wait; + } + } else + retval = -EOPNOTSUPP; mutex_unlock(&acm->port.mutex); return retval; --