Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2993954AbbHHWZh (ORCPT ); Sat, 8 Aug 2015 18:25:37 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:36748 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2993056AbbHHWWq (ORCPT ); Sat, 8 Aug 2015 18:22:46 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Robert Elliott , Peter Hurley Subject: [PATCH 4.1 083/123] serial: core: Fix crashes while echoing when closing Date: Sat, 8 Aug 2015 15:09:21 -0700 Message-Id: <20150808220720.652825983@linuxfoundation.org> X-Mailer: git-send-email 2.5.0 In-Reply-To: <20150808220717.771230091@linuxfoundation.org> References: <20150808220717.771230091@linuxfoundation.org> User-Agent: quilt/0.64 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: 3154 Lines: 85 4.1-stable review patch. If anyone has any objections, please let me know. ------------------ From: Peter Hurley commit e144c58cad6667876173dd76977e9e6557e34941 upstream. While closing, new rx data may be received after the input buffers have been flushed but before stop_rx() halts receiving [1]. The new data might not be processed by flush_to_ldisc() until after uart_shutdown() and normal input processing is re-enabled (ie., tty->closing = 0). The race is outlined below: CPU 0 | CPU 1 | uart_close() | tty_port_close_start() | tty->closing = 1 | tty_ldisc_flush() | | => IRQ | while (LSR & data ready) | uart_insert_char() | tty_flip_buffer_push() | <= EOI stop_rx() | . uart_shutdown() | . free xmit.buf | . tty_port_tty_set(NULL) | . tty->closing = 0 | . | flush_to_ldisc() | n_tty_receive_buf_common() | __receive_buf() | ... | commit_echoes() | uart_flush_chars() | __uart_start() | ** OOPS on port.tty deref ** tty_ldisc_flush() | Input processing must be prevented from echoing (tty->closing = 1) until _after_ the input buffers have been flushed again at the end of uart_close(). [1] In fact, some input may actually be buffered _after_ stop_rx() since the rx interrupt may have already triggered but not yet been handled when stop_rx() disables rx interrupts. Fixes: 2e758910832d ("serial: core: Flush ldisc after dropping port mutex in uart_close()") Reported-by: Robert Elliott Signed-off-by: Peter Hurley Signed-off-by: Greg Kroah-Hartman Signed-off-by: Greg Kroah-Hartman --- drivers/tty/serial/serial_core.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) --- a/drivers/tty/serial/serial_core.c +++ b/drivers/tty/serial/serial_core.c @@ -1409,7 +1409,7 @@ static void uart_close(struct tty_struct mutex_lock(&port->mutex); uart_shutdown(tty, state); tty_port_tty_set(port, NULL); - tty->closing = 0; + spin_lock_irqsave(&port->lock, flags); if (port->blocked_open) { @@ -1435,6 +1435,7 @@ static void uart_close(struct tty_struct mutex_unlock(&port->mutex); tty_ldisc_flush(tty); + tty->closing = 0; } static void uart_wait_until_sent(struct tty_struct *tty, int timeout) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/