release/4.8.18/usb-xhci-fix-possible-wild-pointer.patch

From 409ecdf5cc5bad88a79b341435511c760501ba65 Mon Sep 17 00:00:00 2001
From: Lu Baolu <baolu.lu@linux.intel.com>
Date: Tue, 3 Jan 2017 18:28:46 +0200
Subject: [PATCH] usb: xhci: fix possible wild pointer

commit 2b985467371a58ae44d76c7ba12b0951fee6ed98 upstream.

handle_cmd_completion() frees a command structure which might be still
referenced by xhci->current_cmd.
This might cause problem when xhci->current_cmd is accessed after that.

A real-life case could be like this. The host takes a very long time to
respond to a command, and the command timer is fired at the same time
when the command completion event arrives. The command completion
handler frees xhci->current_cmd before the timer function can grab
xhci->lock. Afterward, timer function grabs the lock and go ahead with
checking and setting members of xhci->current_cmd.

Cc: <stable@vger.kernel.org> # v3.16+
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>

diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c
index 797137e26549..f7431f4df5a3 100644
--- a/drivers/usb/host/xhci-ring.c
+++ b/drivers/usb/host/xhci-ring.c
@@ -1271,14 +1271,18 @@ void xhci_handle_command_timeout(unsigned long data)
 	bool second_timeout = false;
 	xhci = (struct xhci_hcd *) data;
 
-	/* mark this command to be cancelled */
 	spin_lock_irqsave(&xhci->lock, flags);
-	if (xhci->current_cmd) {
-		if (xhci->current_cmd->status == COMP_CMD_ABORT)
-			second_timeout = true;
-		xhci->current_cmd->status = COMP_CMD_ABORT;
+
+	if (!xhci->current_cmd) {
+		spin_unlock_irqrestore(&xhci->lock, flags);
+		return;
 	}
 
+	/* mark this command to be cancelled */
+	if (xhci->current_cmd->status == COMP_CMD_ABORT)
+		second_timeout = true;
+	xhci->current_cmd->status = COMP_CMD_ABORT;
+
 	/* Make sure command ring is running before aborting it */
 	hw_ring_state = xhci_read_64(xhci, &xhci->op_regs->cmd_ring);
 	if ((xhci->cmd_ring_state & CMD_RING_STATE_RUNNING) &&
@@ -1427,6 +1431,8 @@ static void handle_cmd_completion(struct xhci_hcd *xhci,
 		xhci->current_cmd = list_entry(cmd->cmd_list.next,
 					       struct xhci_command, cmd_list);
 		mod_timer(&xhci->cmd_timer, jiffies + XHCI_CMD_DEFAULT_TIMEOUT);
+	} else if (xhci->current_cmd == cmd) {
+		xhci->current_cmd = NULL;
 	}
 
 event_handled:
-- 
2.10.1