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    Subject[PATCH 3.16 150/370] usb: xhci: fix possible wild pointer
    3.16.42-rc1 review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Lu Baolu <baolu.lu@linux.intel.com>

    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.

    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>
    [bwh: Backported to 3.16: adjust context]
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    ---
    --- a/drivers/usb/host/xhci-ring.c
    +++ b/drivers/usb/host/xhci-ring.c
    @@ -1292,13 +1292,16 @@ void xhci_handle_command_timeout(unsigne
    struct xhci_command *cur_cmd = NULL;
    xhci = (struct xhci_hcd *) data;

    - /* mark this command to be cancelled */
    spin_lock_irqsave(&xhci->lock, flags);
    - if (xhci->current_cmd) {
    - cur_cmd = xhci->current_cmd;
    - cur_cmd->status = COMP_CMD_ABORT;
    +
    + if (!xhci->current_cmd) {
    + spin_unlock_irqrestore(&xhci->lock, flags);
    + return;
    }

    + /* mark this command to be cancelled */
    + cur_cmd = xhci->current_cmd;
    + cur_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);
    @@ -1440,6 +1443,8 @@ static void handle_cmd_completion(struct
    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:
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