diff options
| author | Peter Hurley <peter@hurleysoftware.com> | 2014-09-02 17:39:13 -0400 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2014-09-08 16:22:42 -0700 |
| commit | c235ccc1c4d6fd8b7d48b976b87416230ffd5149 (patch) | |
| tree | 57121108b002bd0f74c4f8efce18dbf823564d2a /drivers/tty/serial/serial_core.c | |
| parent | 5e42e9a30cdaae51411a9fd4d7de1dc6a7507038 (diff) | |
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@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'drivers/tty/serial/serial_core.c')
| -rw-r--r-- | drivers/tty/serial/serial_core.c | 7 |
1 files changed, 3 insertions, 4 deletions
diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c index 0742f77ac410..bd20cf51e912 100644 --- a/drivers/tty/serial/serial_core.c +++ b/drivers/tty/serial/serial_core.c @@ -600,12 +600,11 @@ 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); } } |