Re: KASAN: use-after-free Read in p54u_load_firmware_cb

[Alan Stern]

On Sat, 18 May 2019, syzbot wrote:

> Hello,
> 
> syzbot has tested the proposed patch but the reproducer still triggered  
> crash:
> KASAN: use-after-free Read in usb_driver_release_interface
> 
> usb 1-1: Loading firmware file isl3887usb
> usb 1-1: Direct firmware load for isl3887usb failed with error -2
> usb 1-1: Firmware not found.
> p54usb 1-1:0.143: failed to initialize device (-2)
> ==================================================================
> BUG: KASAN: use-after-free in usb_driver_release_interface+0x16b/0x190  
> drivers/usb/core/driver.c:584
> Read of size 8 at addr ffff88808fc31218 by task kworker/0:1/12

Now the bad access is in a different place.  That's a good sign.
In this case it indicates that although udev is still hanging around, 
intf has already been freed.  We really should acquire a reference to 
it instead.

Alan Stern


#syz test: https://github.com/google/kasan.git usb-fuzzer

 drivers/net/wireless/intersil/p54/p54usb.c |   43 ++++++++++++-----------------
 1 file changed, 18 insertions(+), 25 deletions(-)

Index: usb-devel/drivers/net/wireless/intersil/p54/p54usb.c
===================================================================
--- usb-devel.orig/drivers/net/wireless/intersil/p54/p54usb.c
+++ usb-devel/drivers/net/wireless/intersil/p54/p54usb.c
@@ -33,6 +33,8 @@ MODULE_ALIAS("prism54usb");
 MODULE_FIRMWARE("isl3886usb");
 MODULE_FIRMWARE("isl3887usb");
 
+static struct usb_driver p54u_driver;
+
 /*
  * Note:
  *
@@ -921,9 +923,9 @@ static void p54u_load_firmware_cb(const
 {
 	struct p54u_priv *priv = context;
 	struct usb_device *udev = priv->udev;
+	struct usb_interface *intf = priv->intf;
 	int err;
 
-	complete(&priv->fw_wait_load);
 	if (firmware) {
 		priv->fw = firmware;
 		err = p54u_start_ops(priv);
@@ -932,26 +934,22 @@ static void p54u_load_firmware_cb(const
 		dev_err(&udev->dev, "Firmware not found.\n");
 	}
 
-	if (err) {
-		struct device *parent = priv->udev->dev.parent;
-
-		dev_err(&udev->dev, "failed to initialize device (%d)\n", err);
-
-		if (parent)
-			device_lock(parent);
+	complete(&priv->fw_wait_load);
+	/*
+	 * At this point p54u_disconnect may have already freed
+	 * the "priv" context. Do not use it anymore!
+	 */
+	priv = NULL;
 
-		device_release_driver(&udev->dev);
-		/*
-		 * At this point p54u_disconnect has already freed
-		 * the "priv" context. Do not use it anymore!
-		 */
-		priv = NULL;
+	if (err) {
+		dev_err(&intf->dev, "failed to initialize device (%d)\n", err);
 
-		if (parent)
-			device_unlock(parent);
+		usb_lock_device(udev);
+		usb_driver_release_interface(&p54u_driver, intf);
+		usb_unlock_device(udev);
 	}
 
-	usb_put_dev(udev);
+	usb_put_intf(intf);
 }
 
 static int p54u_load_firmware(struct ieee80211_hw *dev,
@@ -972,14 +970,14 @@ static int p54u_load_firmware(struct iee
 	dev_info(&priv->udev->dev, "Loading firmware file %s\n",
 	       p54u_fwlist[i].fw);
 
-	usb_get_dev(udev);
+	usb_get_intf(intf);
 	err = request_firmware_nowait(THIS_MODULE, 1, p54u_fwlist[i].fw,
 				      device, GFP_KERNEL, priv,
 				      p54u_load_firmware_cb);
 	if (err) {
 		dev_err(&priv->udev->dev, "(p54usb) cannot load firmware %s "
 					  "(%d)!\n", p54u_fwlist[i].fw, err);
-		usb_put_dev(udev);
+		usb_put_intf(intf);
 	}
 
 	return err;
@@ -1011,8 +1009,6 @@ static int p54u_probe(struct usb_interfa
 	skb_queue_head_init(&priv->rx_queue);
 	init_usb_anchor(&priv->submitted);
 
-	usb_get_dev(udev);
-
 	/* really lazy and simple way of figuring out if we're a 3887 */
 	/* TODO: should just stick the identification in the device table */
 	i = intf->altsetting->desc.bNumEndpoints;
@@ -1053,10 +1049,8 @@ static int p54u_probe(struct usb_interfa
 		priv->upload_fw = p54u_upload_firmware_net2280;
 	}
 	err = p54u_load_firmware(dev, intf);
-	if (err) {
-		usb_put_dev(udev);
+	if (err)
 		p54_free_common(dev);
-	}
 	return err;
 }
 
@@ -1072,7 +1066,6 @@ static void p54u_disconnect(struct usb_i
 	wait_for_completion(&priv->fw_wait_load);
 	p54_unregister_common(dev);
 
-	usb_put_dev(interface_to_usbdev(intf));
 	release_firmware(priv->fw);
 	p54_free_common(dev);
 }