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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B8942C433F5 for ; Mon, 15 Nov 2021 22:09:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 97EC661029 for ; Mon, 15 Nov 2021 22:09:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1348389AbhKOWMF (ORCPT ); Mon, 15 Nov 2021 17:12:05 -0500 Received: from mail.kernel.org ([198.145.29.99]:42474 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241963AbhKOSbp (ORCPT ); Mon, 15 Nov 2021 13:31:45 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 1869161B49; Mon, 15 Nov 2021 17:59:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1636999163; bh=uCHTnbPd+Ecrib8YuCqOhqtDJNk4FdsnPzegOXc6QTQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=ylGSFps6N1YeU2ZaqJ72MzX38FEj3RYD0ZMCou8ZRZwK+T/fqGpyJqG2H+D6/iVKX bdvLSNXSLAMIQK3GH/rXwtjWcqjsH1kjy+1i6sZ5K/5laJUy0mUo6l28grTTN2U0JH it84d3hsaP3qI14CWzzdgmITS6En3Ei/+OQ4frlQ= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Serge Semin , Serge Semin , Andy Shevchenko , Johan Hovold Subject: [PATCH 5.14 199/849] serial: 8250: fix racy uartclk update Date: Mon, 15 Nov 2021 17:54:42 +0100 Message-Id: <20211115165426.927645500@linuxfoundation.org> X-Mailer: git-send-email 2.33.1 In-Reply-To: <20211115165419.961798833@linuxfoundation.org> References: <20211115165419.961798833@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Johan Hovold commit 211cde4f5817dc88ef7f8f2fa286e57fbf14c8ee upstream. Commit 868f3ee6e452 ("serial: 8250: Add 8250 port clock update method") added a hack to support SoCs where the UART reference clock can change behind the back of the driver but failed to add the proper locking. First, make sure to take a reference to the tty struct to avoid dereferencing a NULL pointer if the clock change races with a hangup. Second, the termios semaphore must be held during the update to prevent a racing termios change. Fixes: 868f3ee6e452 ("serial: 8250: Add 8250 port clock update method") Fixes: c8dff3aa8241 ("serial: 8250: Skip uninitialized TTY port baud rate update") Cc: stable@vger.kernel.org # 5.9 Cc: Serge Semin Tested-by: Serge Semin Reviewed-by: Serge Semin Acked-by: Andy Shevchenko Signed-off-by: Johan Hovold Link: https://lore.kernel.org/r/20211015111422.1027-2-johan@kernel.org Signed-off-by: Greg Kroah-Hartman --- drivers/tty/serial/8250/8250_port.c | 21 +++++++++++++++++---- 1 file changed, 17 insertions(+), 4 deletions(-) --- a/drivers/tty/serial/8250/8250_port.c +++ b/drivers/tty/serial/8250/8250_port.c @@ -2696,21 +2696,32 @@ static unsigned int serial8250_get_baud_ void serial8250_update_uartclk(struct uart_port *port, unsigned int uartclk) { struct uart_8250_port *up = up_to_u8250p(port); + struct tty_port *tport = &port->state->port; unsigned int baud, quot, frac = 0; struct ktermios *termios; + struct tty_struct *tty; unsigned long flags; - mutex_lock(&port->state->port.mutex); + tty = tty_port_tty_get(tport); + if (!tty) { + mutex_lock(&tport->mutex); + port->uartclk = uartclk; + mutex_unlock(&tport->mutex); + return; + } + + down_write(&tty->termios_rwsem); + mutex_lock(&tport->mutex); if (port->uartclk == uartclk) goto out_lock; port->uartclk = uartclk; - if (!tty_port_initialized(&port->state->port)) + if (!tty_port_initialized(tport)) goto out_lock; - termios = &port->state->port.tty->termios; + termios = &tty->termios; baud = serial8250_get_baud_rate(port, termios, NULL); quot = serial8250_get_divisor(port, baud, &frac); @@ -2727,7 +2738,9 @@ void serial8250_update_uartclk(struct ua serial8250_rpm_put(up); out_lock: - mutex_unlock(&port->state->port.mutex); + mutex_unlock(&tport->mutex); + up_write(&tty->termios_rwsem); + tty_kref_put(tty); } EXPORT_SYMBOL_GPL(serial8250_update_uartclk);