patch "xhci: Fix use after free for URB cancellation on a reallocated" added to usb-linus

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    xhci: Fix use after free for URB cancellation on a reallocated

to my usb git tree which can be found at
    git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git
in the usb-linus branch.

The patch will show up in the next release of the linux-next tree
(usually sometime within the next 24 hours during the week.)

The patch will hopefully also be merged in Linus's tree for the
next -rc kernel release.

If you have any questions about this process, please let me know.


>From 4937213ba7fafa13f30496b3965ffe93970d8b53 Mon Sep 17 00:00:00 2001
From: Mathias Nyman <mathias.nyman@linux.intel.com>
Date: Fri, 31 Aug 2018 17:24:43 +0300
Subject: xhci: Fix use after free for URB cancellation on a reallocated
 endpoint

Make sure the cancelled URB is on the current endpoint ring.

If the endpoint ring has been reallocated since the URB was enqueued
then the URB may contain TD and TRB pointers to a already freed ring.
In this the case return the URB without touching any of the freed ring
structure data.

Don't try to stop the ring. It would be useless.

This can occur if endpoint is not flushed before it is dropped and
re-added, which is the case in usb_set_interface() as xhci does
things in an odd order.

Cc: <stable@vger.kernel.org>
Tested-by: Sudip Mukherjee <sudipm.mukherjee@gmail.com>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/usb/host/xhci.c | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/drivers/usb/host/xhci.c b/drivers/usb/host/xhci.c
index 61f48b17e57b..0420eefa647a 100644
--- a/drivers/usb/host/xhci.c
+++ b/drivers/usb/host/xhci.c
@@ -37,6 +37,21 @@ static unsigned long long quirks;
 module_param(quirks, ullong, S_IRUGO);
 MODULE_PARM_DESC(quirks, "Bit flags for quirks to be enabled as default");
 
+static bool td_on_ring(struct xhci_td *td, struct xhci_ring *ring)
+{
+	struct xhci_segment *seg = ring->first_seg;
+
+	if (!td || !td->start_seg)
+		return false;
+	do {
+		if (seg == td->start_seg)
+			return true;
+		seg = seg->next;
+	} while (seg && seg != ring->first_seg);
+
+	return false;
+}
+
 /* TODO: copied from ehci-hcd.c - can this be refactored? */
 /*
  * xhci_handshake - spin reading hc until handshake completes or fails
@@ -1571,6 +1586,21 @@ static int xhci_urb_dequeue(struct usb_hcd *hcd, struct urb *urb, int status)
 		goto done;
 	}
 
+	/*
+	 * check ring is not re-allocated since URB was enqueued. If it is, then
+	 * make sure none of the ring related pointers in this URB private data
+	 * are touched, such as td_list, otherwise we overwrite freed data
+	 */
+	if (!td_on_ring(&urb_priv->td[0], ep_ring)) {
+		xhci_err(xhci, "Canceled URB td not found on endpoint ring");
+		for (i = urb_priv->num_tds_done; i < urb_priv->num_tds; i++) {
+			td = &urb_priv->td[i];
+			if (!list_empty(&td->cancelled_td_list))
+				list_del_init(&td->cancelled_td_list);
+		}
+		goto err_giveback;
+	}
+
 	if (xhci->xhc_state & XHCI_STATE_HALTED) {
 		xhci_dbg_trace(xhci, trace_xhci_dbg_cancel_urb,
 				"HC halted, freeing TD manually.");
-- 
2.18.0