linux-kernel - [PATCH 4.9 35/65] usbip: fix possibility of dereference by NULLL pointer in vhci

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Date:   Mon, 11 Nov 2019 19:28:35 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Nobuo Iwata <nobuo.iwata@...ixerox.co.jp>
Subject: [PATCH 4.9 35/65] usbip: fix possibility of dereference by NULLL pointer in vhci_hcd.c

From: Nobuo Iwata <nobuo.iwata@...ixerox.co.jp>

commit d79cda045e3bacb7e754a5324cd3d4ce80708eb1 upstream.

This patch fixes possibility of dereference by NULLL pointer in "[PATCH
v5 1/3] usbip: vhci extension: modifications to vhci driver" which has
been merged to 4.9-rc1. It occurs when a URB with pointer to invalid
USB/IP device is enqueued in race condition against detach operation.

A pointer was passed to vdev_to_vhci() before NULL check.
In vdev_to_vhci(), there's a dereference by the pointer.

This patch moves vdev_to_vhci() after NULL check of the pointer.

Signed-off-by: Nobuo Iwata <nobuo.iwata@...ixerox.co.jp>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/usb/usbip/vhci_hcd.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/drivers/usb/usbip/vhci_hcd.c
+++ b/drivers/usb/usbip/vhci_hcd.c
@@ -465,13 +465,14 @@ static void vhci_tx_urb(struct urb *urb)
 {
 	struct vhci_device *vdev = get_vdev(urb->dev);
 	struct vhci_priv *priv;
-	struct vhci_hcd *vhci = vdev_to_vhci(vdev);
+	struct vhci_hcd *vhci;
 	unsigned long flags;
 
 	if (!vdev) {
 		pr_err("could not get virtual device");
 		return;
 	}
+	vhci = vdev_to_vhci(vdev);
 
 	priv = kzalloc(sizeof(struct vhci_priv), GFP_ATOMIC);
 	if (!priv) {