netdev - [PATCH net] net: hso: fix NULL-deref on tty registration failure

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Message-Id: <20210426094542.22578-1-johan@kernel.org>
Date:   Mon, 26 Apr 2021 11:45:42 +0200
From:   Johan Hovold <johan@...nel.org>
To:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-usb@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, Johan Hovold <johan@...nel.org>,
        stable@...r.kernel.org
Subject: [PATCH net] net: hso: fix NULL-deref on tty registration failure

If resource allocation and registration fail for a muxed tty device
(e.g. if there are no more minor numbers) the driver should not try to
deregister the never-registered tty.

Fix up the error handling to avoid dereferencing a NULL pointer when
attempting to remove the character device:

	BUG: kernel NULL pointer dereference, address: 0000000000000064
	[...]
	RIP: 0010:cdev_del+0x4/0x20
	[...]
	Call Trace:
	 tty_unregister_device+0x34/0x50
	 hso_probe+0x1d1/0x57e [hso]

Fixes: 72dc1c096c70 ("HSO: add option hso driver")
Cc: stable@...r.kernel.org	# 2.6.27
Signed-off-by: Johan Hovold <johan@...nel.org>
---
 drivers/net/usb/hso.c | 12 +++++-------
 1 file changed, 5 insertions(+), 7 deletions(-)

diff --git a/drivers/net/usb/hso.c b/drivers/net/usb/hso.c
index cfad5b36bd8e..81ff54e9587f 100644
--- a/drivers/net/usb/hso.c
+++ b/drivers/net/usb/hso.c
@@ -2710,14 +2710,14 @@ struct hso_device *hso_create_mux_serial_device(struct usb_interface *interface,
 
 	serial = kzalloc(sizeof(*serial), GFP_KERNEL);
 	if (!serial)
-		goto exit;
+		goto err_free_dev;
 
 	hso_dev->port_data.dev_serial = serial;
 	serial->parent = hso_dev;
 
 	if (hso_serial_common_create
 	    (serial, 1, CTRL_URB_RX_SIZE, CTRL_URB_TX_SIZE))
-		goto exit;
+		goto err_free_serial;
 
 	serial->tx_data_length--;
 	serial->write_data = hso_mux_serial_write_data;
@@ -2733,11 +2733,9 @@ struct hso_device *hso_create_mux_serial_device(struct usb_interface *interface,
 	/* done, return it */
 	return hso_dev;
 
-exit:
-	if (serial) {
-		tty_unregister_device(tty_drv, serial->minor);
-		kfree(serial);
-	}
+err_free_serial:
+	kfree(serial);
+err_free_dev:
 	kfree(hso_dev);
 	return NULL;
 
-- 
2.26.3