virtio: console: Ensure only one process can have a port open at a time

Add a guest_connected field that ensures only one process
can have a port open at a time.

This also ensures we don't have a race when we later add support for
dropping buffers when closing the char dev and buffer caching is turned
off for the particular port.

Signed-off-by: Amit Shah <amit.shah@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

1 files changed, 17 insertions, 1 deletions

diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
index ece1546fbb20..5e3503a31312 100644
--- a/drivers/char/virtio_console.c
+++ b/drivers/char/virtio_console.c
@@ -175,6 +175,9 @@ struct port {
 
         /* Is the host device open */
         bool host_connected;
+
+        /* We should allow only one process to open a port */
+        bool guest_connected;
 };
 
 /* This is the very early arch-specified put chars function. */
@@ -528,6 +531,8 @@ static int port_fops_release(struct inode *inode, struct file *filp)
         /* Notify host of port being closed */
         send_control_msg(port, VIRTIO_CONSOLE_PORT_OPEN, 0);
 
+        port->guest_connected = false;
+
         return 0;
 }
 
@@ -546,6 +551,16 @@ static int port_fops_open(struct inode *inode, struct file *filp)
         if (is_console_port(port))
                 return -ENXIO;
 
+        /* Allow only one process to open a particular port at a time */
+        spin_lock_irq(&port->inbuf_lock);
+        if (port->guest_connected) {
+                spin_unlock_irq(&port->inbuf_lock);
+                return -EMFILE;
+        }
+
+        port->guest_connected = true;
+        spin_unlock_irq(&port->inbuf_lock);
+
         /* Notify host of port being opened */
         send_control_msg(filp->private_data, VIRTIO_CONSOLE_PORT_OPEN, 1);
 
@@ -709,6 +724,7 @@ int init_port_console(struct port *port)
         pdrvdata.next_vtermno++;
         list_add_tail(&port->cons.list, &pdrvdata.consoles);
         spin_unlock_irq(&pdrvdata_lock);
+        port->guest_connected = true;
 
         /* Notify host of port being opened */
         send_control_msg(port, VIRTIO_CONSOLE_PORT_OPEN, 1);
@@ -856,7 +872,7 @@ static int add_port(struct ports_device *portdev, u32 id)
         port->inbuf = NULL;
         port->cons.hvc = NULL;
 
-        port->host_connected = false;
+        port->host_connected = port->guest_connected = false;
 
         port->in_vq = portdev->in_vqs[port->id];
         port->out_vq = portdev->out_vqs[port->id];