Commit db7f19c0 authored by Arnaud Pouliquen's avatar Arnaud Pouliquen Committed by Greg Kroah-Hartman
Browse files

tty: rpmsg: Fix race condition releasing tty port 



The tty_port struct is part of the rpmsg_tty_port structure.
The issue is that the rpmsg_tty_port structure is freed on
rpmsg_tty_remove while it is still referenced in the tty_struct.
Its release is not predictable due to workqueues.

For instance following ftrace shows that rpmsg_tty_close is called after
rpmsg_tty_release_cport:

     nr_test.sh-389     [000] .....   212.093752: rpmsg_tty_remove <-rpmsg_dev_
remove
             cat-1191    [001] .....   212.095697: tty_release <-__fput
      nr_test.sh-389     [000] .....   212.099166: rpmsg_tty_release_cport <-rpm
sg_tty_remove
             cat-1191    [001] .....   212.115352: rpmsg_tty_close <-tty_release
             cat-1191    [001] .....   212.115371: release_tty <-tty_release_str

As consequence, the port must be free only when user has released the TTY
interface.

This path :
- Introduce the .destruct port tty ops function to release the allocated
  rpmsg_tty_port structure.
- Introduce the .hangup tty ops function to call tty_port_hangup.
- Manages the tty port refcounting to trig the .destruct port ops,
- Introduces the rpmsg_tty_cleanup function to ensure that the TTY is
  removed before decreasing the port refcount.

Fixes: 7c0408d8 ("tty: add rpmsg driver")
Cc: stable <stable@vger.kernel.org>
Signed-off-by: default avatarArnaud Pouliquen <arnaud.pouliquen@foss.st.com>
Link: https://lore.kernel.org/r/20220104163545.34710-1-arnaud.pouliquen@foss.st.com


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent f23653fe

drivers/tty/rpmsg_tty.c

+26 −14
Original line number Diff line number Diff line
@@ -50,10 +50,17 @@ static int rpmsg_tty_cb(struct rpmsg_device *rpdev, void *data, int len, void *p 
static int rpmsg_tty_install(struct tty_driver *driver, struct tty_struct *tty)

{

	struct rpmsg_tty_port *cport = idr_find(&tty_idr, tty->index);

	struct tty_port *port;



	tty->driver_data = cport;



	return tty_port_install(&cport->port, driver, tty);

	port = tty_port_get(&cport->port);

	return tty_port_install(port, driver, tty);

}



static void rpmsg_tty_cleanup(struct tty_struct *tty)

{

	tty_port_put(tty->port);

}



static int rpmsg_tty_open(struct tty_struct *tty, struct file *filp)
@@ -106,12 +113,19 @@ static unsigned int rpmsg_tty_write_room(struct tty_struct *tty) 
	return size;

}



static void rpmsg_tty_hangup(struct tty_struct *tty)

{

	tty_port_hangup(tty->port);

}



static const struct tty_operations rpmsg_tty_ops = {

	.install	= rpmsg_tty_install,

	.open		= rpmsg_tty_open,

	.close		= rpmsg_tty_close,

	.write		= rpmsg_tty_write,

	.write_room	= rpmsg_tty_write_room,

	.hangup		= rpmsg_tty_hangup,

	.cleanup	= rpmsg_tty_cleanup,

};



static struct rpmsg_tty_port *rpmsg_tty_alloc_cport(void)
@@ -137,8 +151,10 @@ static struct rpmsg_tty_port *rpmsg_tty_alloc_cport(void) 
	return cport;

}



static void rpmsg_tty_release_cport(struct rpmsg_tty_port *cport)

static void rpmsg_tty_destruct_port(struct tty_port *port)

{

	struct rpmsg_tty_port *cport = container_of(port, struct rpmsg_tty_port, port);



	mutex_lock(&idr_lock);

	idr_remove(&tty_idr, cport->id);

	mutex_unlock(&idr_lock);
@@ -146,7 +162,10 @@ static void rpmsg_tty_release_cport(struct rpmsg_tty_port *cport) 
	kfree(cport);

}



static const struct tty_port_operations rpmsg_tty_port_ops = { };

static const struct tty_port_operations rpmsg_tty_port_ops = {

	.destruct = rpmsg_tty_destruct_port,

};





static int rpmsg_tty_probe(struct rpmsg_device *rpdev)

{
@@ -166,7 +185,8 @@ static int rpmsg_tty_probe(struct rpmsg_device *rpdev) 
					   cport->id, dev);

	if (IS_ERR(tty_dev)) {

		ret = dev_err_probe(dev, PTR_ERR(tty_dev), "Failed to register tty port\n");

		goto err_destroy;

		tty_port_put(&cport->port);

		return ret;

	}



	cport->rpdev = rpdev;
@@ -177,12 +197,6 @@ static int rpmsg_tty_probe(struct rpmsg_device *rpdev) 
		rpdev->src, rpdev->dst, cport->id);



	return 0;



err_destroy:

	tty_port_destroy(&cport->port);

	rpmsg_tty_release_cport(cport);



	return ret;

}



static void rpmsg_tty_remove(struct rpmsg_device *rpdev)
@@ -192,13 +206,11 @@ static void rpmsg_tty_remove(struct rpmsg_device *rpdev) 
	dev_dbg(&rpdev->dev, "Removing rpmsg tty device %d\n", cport->id);



	/* User hang up to release the tty */

	if (tty_port_initialized(&cport->port))

	tty_port_tty_hangup(&cport->port, false);



	tty_unregister_device(rpmsg_tty_driver, cport->id);



	tty_port_destroy(&cport->port);

	rpmsg_tty_release_cport(cport);

	tty_port_put(&cport->port);

}



static struct rpmsg_device_id rpmsg_driver_tty_id_table[] = {