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    Subject[PATCH 4.9 035/206] usb: xhci: fix possible wild pointer
    Date
    4.9-stable 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>

    ---
    drivers/usb/host/xhci-ring.c | 16 +++++++++++-----
    1 file changed, 11 insertions(+), 5 deletions(-)

    --- a/drivers/usb/host/xhci-ring.c
    +++ b/drivers/usb/host/xhci-ring.c
    @@ -1271,14 +1271,18 @@ void xhci_handle_command_timeout(unsigne
    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->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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