linux-kernel - [PATCH 04/26] serial: core: Fix x

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Tue,  2 Sep 2014 17:39:13 -0400
From:	Peter Hurley <peter@...leysoftware.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Jiri Slaby <jslaby@...e.cz>,
	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
	Peter Hurley <peter@...leysoftware.com>
Subject: [PATCH 04/26] serial: core: Fix x_char race

The UART driver is expected to clear port->x_char after
transmission while holding the port->lock. However, the serial
core fails to take the port->lock before assigning port->xchar.
This allows for the following race

CPU 0                         |  CPU 1
                              |
                              | serial8250_handle_irq
                              |   ...
                              |   serial8250_tx_chars
                              |     if (port->x_char)
                              |       serial_out(up, UART_TX, port->x_char)
uart_send_xchar               |
  port->x_char = ch           |
                              |       port->x_char = 0
  port->ops->start_tx()       |
                              |

The x_char on CPU 0 will never be sent.

Take the port->lock in uart_send_xchar() before assigning port->x_char.

Signed-off-by: Peter Hurley <peter@...leysoftware.com>
---
 drivers/tty/serial/serial_core.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index 87cde4c..a68bff0 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -596,12 +596,11 @@ static void uart_send_xchar(struct tty_struct *tty, char ch)
 	if (port->ops->send_xchar)
 		port->ops->send_xchar(port, ch);
 	else {
+		spin_lock_irqsave(&port->lock, flags);
 		port->x_char = ch;
-		if (ch) {
-			spin_lock_irqsave(&port->lock, flags);
+		if (ch)
 			port->ops->start_tx(port);
-			spin_unlock_irqrestore(&port->lock, flags);
-		}
+		spin_unlock_irqrestore(&port->lock, flags);
 	}
 }
 
-- 
2.1.0

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/