net: usb: lan78xx: Fix double free issue with interrupt buffer allocation

In lan78xx_probe(), the buffer `buf` was being freed twice: once
implicitly through `usb_free_urb(dev->urb_intr)` with the
`URB_FREE_BUFFER` flag and again explicitly by `kfree(buf)`. This caused
a double free issue.

To resolve this, reordered `kmalloc()` and `usb_alloc_urb()` calls to
simplify the initialization sequence and removed the redundant
`kfree(buf)`.  Now, `buf` is allocated after `usb_alloc_urb()`, ensuring
it is correctly managed by  `usb_fill_int_urb()` and freed by
`usb_free_urb()` as intended.

Fixes: a6df95c ("lan78xx: Fix memory allocation bug")
Cc: John Efstathiades <john.efstathiades@pebblebay.com>
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Link: https://patch.msgid.link/20241116130558.1352230-1-o.rempel@pengutronix.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: olerem

drivers/net/usb/lan78xx.c

@@ -4414,37 +4414,38 @@ static int lan78xx_probe(struct usb_interface *intf,
 
 	period = ep_intr->desc.bInterval;
 	maxp = usb_maxpacket(dev->udev, dev->pipe_intr);
-	buf = kmalloc(maxp, GFP_KERNEL);
-	if (!buf) {
+
+	dev->urb_intr = usb_alloc_urb(0, GFP_KERNEL);
+	if (!dev->urb_intr) {
 		ret = -ENOMEM;
 		goto out5;
 	}
 
-	dev->urb_intr = usb_alloc_urb(0, GFP_KERNEL);
-	if (!dev->urb_intr) {
+	buf = kmalloc(maxp, GFP_KERNEL);
+	if (!buf) {
 		ret = -ENOMEM;
-		goto out6;
-	} else {
-		usb_fill_int_urb(dev->urb_intr, dev->udev,
-				 dev->pipe_intr, buf, maxp,
-				 intr_complete, dev, period);
-		dev->urb_intr->transfer_flags |= URB_FREE_BUFFER;
+		goto free_urbs;
 	}
 
+	usb_fill_int_urb(dev->urb_intr, dev->udev,
+			 dev->pipe_intr, buf, maxp,
+			 intr_complete, dev, period);
+	dev->urb_intr->transfer_flags |= URB_FREE_BUFFER;
+
 	dev->maxpacket = usb_maxpacket(dev->udev, dev->pipe_out);
 
 	/* Reject broken descriptors. */
 	if (dev->maxpacket == 0) {
 		ret = -ENODEV;
-		goto out6;
+		goto free_urbs;
 	}
 
 	/* driver requires remote-wakeup capability during autosuspend. */
 	intf->needs_remote_wakeup = 1;
 
 	ret = lan78xx_phy_init(dev);
 	if (ret < 0)
-		goto out7;
+		goto free_urbs;
 
 	ret = register_netdev(netdev);
 	if (ret != 0) {
@@ -4466,10 +4467,8 @@ static int lan78xx_probe(struct usb_interface *intf,
 
 out8:
 	phy_disconnect(netdev->phydev);
-out7:
+free_urbs:
 	usb_free_urb(dev->urb_intr);
-out6:
-	kfree(buf);
 out5:
 	lan78xx_unbind(dev, intf);
 out4: