Re: [PATCH v2 2/5] usb: xhci: Fix potential memory leak in xhci_disable_slot()

[Mathias Nyman]

On 27.07.2017 05:21, Lu Baolu wrote:
> xhci_disable_slot() allows the invoker to pass a command pointer
> as paramenter. Otherwise, it will allocate one. This will cause
> memory leak when a command structure was allocated inside of this
> function while queuing command trb fails. Another problem comes up
> when the invoker passed a command pointer, but xhci_disable_slot()
> frees it when it detects a dead host.
>
> This patch fixes these two problems by removing the command parameter
> from xhci_disable_slot().
>
> Fixes: f9e609b82479 ("usb: xhci: Add helper function xhci_disable_slot().")
> Cc: Guoqing Zhang <guoqing.zhang@xxxxxxxxx>
> Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> ---
>   drivers/usb/host/xhci-hub.c |  2 +-
>   drivers/usb/host/xhci.c     | 30 +++++++++---------------------
>   drivers/usb/host/xhci.h     |  3 +--
>   3 files changed, 11 insertions(+), 24 deletions(-)
>
> diff --git a/drivers/usb/host/xhci-hub.c b/drivers/usb/host/xhci-hub.c
> index 00721e8..c862d53 100644
> --- a/drivers/usb/host/xhci-hub.c
> +++ b/drivers/usb/host/xhci-hub.c
> @@ -612,7 +612,7 @@ static int xhci_enter_test_mode(struct xhci_hcd *xhci,
>   	xhci_dbg(xhci, "Disable all slots\n");
>   	spin_unlock_irqrestore(&xhci->lock, *flags);
>   	for (i = 1; i <= HCS_MAX_SLOTS(xhci->hcs_params1); i++) {
> -		retval = xhci_disable_slot(xhci, NULL, i);
> +		retval = xhci_disable_slot(xhci, i);
>   		if (retval)
>   			xhci_err(xhci, "Failed to disable slot %d, %d. Enter test mode anyway\n",
>   				 i, retval);
> diff --git a/drivers/usb/host/xhci.c b/drivers/usb/host/xhci.c
> index e69073f..cb2461a 100644
> --- a/drivers/usb/host/xhci.c
> +++ b/drivers/usb/host/xhci.c
> @@ -3519,11 +3519,6 @@ static void xhci_free_dev(struct usb_hcd *hcd, struct usb_device *udev)
>   	struct xhci_virt_device *virt_dev;
>   	struct xhci_slot_ctx *slot_ctx;
>   	int i, ret;
> -	struct xhci_command *command;
> -
> -	command = xhci_alloc_command(xhci, false, false, GFP_KERNEL);
> -	if (!command)
> -		return;
>
>   #ifndef CONFIG_USB_DEFAULT_PERSIST
>   	/*
> @@ -3539,10 +3534,8 @@ static void xhci_free_dev(struct usb_hcd *hcd, struct usb_device *udev)
>   	/* If the host is halted due to driver unload, we still need to free the
>   	 * device.
>   	 */
> -	if (ret <= 0 && ret != -ENODEV) {
> -		kfree(command);
> +	if (ret <= 0 && ret != -ENODEV)
>   		return;
> -	}
>
>   	virt_dev = xhci->devs[udev->slot_id];
>   	slot_ctx = xhci_get_slot_ctx(xhci, virt_dev->out_ctx);
> @@ -3554,22 +3547,21 @@ static void xhci_free_dev(struct usb_hcd *hcd, struct usb_device *udev)
>   		del_timer_sync(&virt_dev->eps[i].stop_cmd_timer);
>   	}
>
> -	xhci_disable_slot(xhci, command, udev->slot_id);
> +	xhci_disable_slot(xhci, udev->slot_id);
>   	/*
>   	 * Event command completion handler will free any data structures
>   	 * associated with the slot.  XXX Can free sleep?
>   	 */
>   }
>
> -int xhci_disable_slot(struct xhci_hcd *xhci, struct xhci_command *command,
> -			u32 slot_id)
> +int xhci_disable_slot(struct xhci_hcd *xhci, u32 slot_id)
>   {
> +	struct xhci_command *command;
>   	unsigned long flags;
>   	u32 state;
>   	int ret = 0;
>
> -	if (!command)
> -		command = xhci_alloc_command(xhci, false, false, GFP_KERNEL);
> +	command = xhci_alloc_command(xhci, false, false, GFP_KERNEL);
>   	if (!command)
>   		return -ENOMEM;
>
> @@ -3588,7 +3580,7 @@ int xhci_disable_slot(struct xhci_hcd *xhci, struct xhci_command *command,
>   				slot_id);
>   	if (ret) {
>   		spin_unlock_irqrestore(&xhci->lock, flags);
> -		xhci_dbg(xhci, "FIXME: allocate a command ring segment\n");
> +		kfree(command);
>   		return ret;
>   	}
>   	xhci_ring_cmd_db(xhci);
> @@ -3663,6 +3655,8 @@ int xhci_alloc_dev(struct usb_hcd *hcd, struct usb_device *udev)
>   		return 0;
>   	}
>
> +	xhci_free_command(xhci, command);
> +
>   	if ((xhci->quirks & XHCI_EP_LIMIT_QUIRK)) {
>   		spin_lock_irqsave(&xhci->lock, flags);
>   		ret = xhci_reserve_host_control_ep_resources(xhci);
> @@ -3698,18 +3692,12 @@ int xhci_alloc_dev(struct usb_hcd *hcd, struct usb_device *udev)
>   		pm_runtime_get_noresume(hcd->self.controller);
>   #endif
>
> -
> -	xhci_free_command(xhci, command);
>   	/* Is this a LS or FS device under a HS hub? */
>   	/* Hub or peripherial? */
>   	return 1;
>
>   disable_slot:
> -	/* Disable slot, if we can do it without mem alloc */
> -	kfree(command->completion);
> -	command->completion = NULL;
> -	command->status = 0;
> -	return xhci_disable_slot(xhci, command, udev->slot_id);
> +	return xhci_disable_slot(xhci, udev->slot_id);

avoiding allocating a new command after failing to allocate a virt dev was
probably the reason why xhci_disable_slot() supported a command
as a parameter in the first place.

But this is such a small corner case, and your patch fixes two more likely issues,
and simplifies the code a lot so I think It's well worth it

-Mathias