linux-kernel - Re: [BUG] usb: xhci: Possible resource leaks when xhci

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Date:   Tue, 14 May 2019 18:55:11 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Jia-Ju Bai <baijiaju1990@...il.com>
Cc:     mathias.nyman@...el.com, linux-usb@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [BUG] usb: xhci: Possible resource leaks when xhci_run() fails

On Tue, May 14, 2019 at 10:58:05PM +0800, Jia-Ju Bai wrote:
> xhci_pci_setup() is assigned to hc_driver.reset;
> xhci_run() is assigned to hc_driver.start();
> xhci_stop() is assigned to hc_driver.stop().
> 
> xhci_pci_setup() calls xhci_gen_setup, which calls xhci_init(). And
> xhci_init() calls xhci_mem_init() to allocate resources.
> 
> xhci_stop() calls xhci_mem_cleanup(), to release the resources allocated in
> xhci_mem_init() (also namely xhci_pci_setup()).
> 
> xhci_run() can fail, because xhci_try_enable_msi() or xhci_alloc_command()
> in this function can fail.
> 
> In drivers/usb/core/hcd.c:
>     retval = hcd->driver->reset(hcd);
>     if (retval < 0) {
>         ......
>         goto err_hcd_driver_setup;
>     }
>     ......
>     retval = hcd->driver->start(hcd);
>     if (retval < 0) {
>         ......
>         goto err_hcd_driver_start;
>     }
>     .......
>     hcd->driver->stop(hcd);
>     hcd->state = HC_STATE_HALT;
>     clear_bit(HCD_FLAG_POLL_RH, &hcd->flags);
>     del_timer_sync(&hcd->rh_timer);
> err_hcd_driver_start:
>     if (usb_hcd_is_primary_hcd(hcd) && hcd->irq > 0)
>         free_irq(irqnum, hcd);
> err_request_irq:
> err_hcd_driver_setup:
> err_set_rh_speed:
>     usb_put_invalidate_rhdev(hcd);
> err_allocate_root_hub:
>     usb_deregister_bus(&hcd->self);
> err_register_bus:
>     hcd_buffer_destroy(hcd);
> err_create_buf:
>     usb_phy_roothub_power_off(hcd->phy_roothub);
> err_usb_phy_roothub_power_on:
>     usb_phy_roothub_exit(hcd->phy_roothub);
> 
> Thus, when hcd->driver->reset() succeeds and hcd->driver->start() fails,
> hcd->driver->stop() is not called.
> 
> Namely, when xhci_pci_setup() successfully allocates resources, and
> xhci_run() fails, xhci_stop() is not called to release the resources.
> For this reason, resource leaks occur in this case.
> 
> I check the code of the ehci driver, uhci driver and ohci driver, and find
> that they do not have such problem, because:
> In the ehci driver, ehci_run() (namely hcd->driver->start()) never fails.
> In the uhci driver, all the resources are allocated in uhci_start (namely
> hcd->driver->start()), and no resources are allocated in uhci_pci_init()
> (namely hcd->driver->reset()).
> In the ohci driver, ohci_setup() (namely hcd->driver->reset()) also
> allocates resources. But when ohci_start() (namely hcd->driver->start()) is
> going to fail, ohci_stop() is directly called to release the resources
> allocated by ohci_setup().
> 
> Thus, there are two possible ways of fixing bugs:
> 1) Call xhci_stop() when xhci_run() is going to fail (like the ohci driver)
> 2) Move all resource-allocation operations into xhci_run() (like the uhci
> driver).
> 
> I am not sure whether these ways are correct, so I only report bugs.

Can you create a patch to show how you would fix this potential issue?
Given that making this type of thing fail is pretty rare, it's not a
real high priority to get to, so it might be a while for anyone here to
look at it.

thanks,

greg k-h