From 880de403777376e50bdf60def359fa50a722006f Mon Sep 17 00:00:00 2001
From: Johan Hovold <johan@kernel.org>
Date: Fri, 8 Oct 2021 12:25:45 +0300
Subject: [PATCH] USB: xhci: dbc: fix tty registration race
Git-commit: 880de403777376e50bdf60def359fa50a722006f
References: git-fixes
Patch-mainline: v5.15-rc6

Make sure to allocate resources before registering the tty device to
avoid having a racing open() and write() fail to enable rx or
dereference a NULL pointer when accessing the uninitialised fifo.

Fixes: dfba2174dc42 ("usb: xhci: Add DbC support in xHCI driver")
Cc: stable@vger.kernel.org      # 4.16
Cc: Lu Baolu <baolu.lu@linux.intel.com>
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Link: https://lore.kernel.org/r/20211008092547.3996295-4-mathias.nyman@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Oliver Neukum <oneukum@suse.com>
---
 drivers/usb/host/xhci-dbgtty.c |   28 +++++++++++++---------------
 1 file changed, 13 insertions(+), 15 deletions(-)

--- a/drivers/usb/host/xhci-dbgtty.c
+++ b/drivers/usb/host/xhci-dbgtty.c
@@ -447,40 +447,38 @@ int xhci_dbc_tty_register_device(struct
 	struct dbc_port		*port = &dbc->port;
 
 	xhci_dbc_tty_init_port(xhci, port);
-	tty_dev = tty_port_register_device(&port->port,
-					   dbc_tty_driver, 0, NULL);
-	if (IS_ERR(tty_dev)) {
-		ret = PTR_ERR(tty_dev);
-		goto register_fail;
-	}
 
 	ret = kfifo_alloc(&port->write_fifo, DBC_WRITE_BUF_SIZE, GFP_KERNEL);
 	if (ret)
-		goto buf_alloc_fail;
+		goto err_exit_port;
 
 	ret = xhci_dbc_alloc_requests(port->in, &port->read_pool,
 				      dbc_read_complete);
 	if (ret)
-		goto request_fail;
+		goto err_free_fifo;
 
 	ret = xhci_dbc_alloc_requests(port->out, &port->write_pool,
 				      dbc_write_complete);
 	if (ret)
-		goto request_fail;
+		goto err_free_requests;
+
+	tty_dev = tty_port_register_device(&port->port,
+					   dbc_tty_driver, 0, NULL);
+	if (IS_ERR(tty_dev)) {
+		ret = PTR_ERR(tty_dev);
+		goto err_free_requests;
+	}		
 
 	port->registered = true;
 
 	return 0;
 
-request_fail:
+err_free_requests:
 	xhci_dbc_free_requests(port->in, &port->read_pool);
 	xhci_dbc_free_requests(port->out, &port->write_pool);
+err_free_fifo:
 	kfifo_free(&port->write_fifo);
-
-buf_alloc_fail:
-	tty_unregister_device(dbc_tty_driver, 0);
-
-register_fail:
+err_exit_port:
 	xhci_dbc_tty_exit_port(port);
 
 	xhci_err(xhci, "can't register tty port, err %d\n", ret);