Re: [PATCH] drivers: usb: host: fix NULL pointer dereferences triggered by unhandled errors in xhci_create_rhub_port_array()

[Mathias Nyman <mathias.nyman@linux.intel.com>]

On 21.4.2022 15.21, Fu Zixuan wrote:
> On Thu, 21 Apr 2022 at 20:06, Greg KH <gregkh@linuxfoundation.org> wrote:
>>
>> On Thu, Apr 21, 2022 at 07:55:28PM +0800, Fu Zixuan wrote:
>>> On Thu, 21 Apr 2022 at 18:07, Greg KH <gregkh@linuxfoundation.org> wrote:
>>>>
>>>> On Thu, Apr 21, 2022 at 05:42:36PM +0800, Zixuan Fu wrote:
>>>>> In xhci_create_rhub_port_array(), when rhub->num_ports is zero,
>>>>> rhub->ports would not be set; when kcalloc_node() fails, rhub->ports
>>>>> would be set to NULL. In these two cases, xhci_create_rhub_port_array()
>>>>> just returns void, and thus its callers are unaware of the error.
>>>>>
>>>>> Then rhub->ports is dereferenced in xhci_usb3_hub_descriptor() or
>>>>> xhci_usb2_hub_descriptor().
>>>>>
>>>>> To fix the bug, xhci_setup_port_arrays() should return an integer to
>>>>> indicate a possible error, and its callers should handle the error.
>>>>>
>>>>> Here is the log when this bug occurred in our fault-injection testing:
>>>>>
>>>>> [   24.001309] BUG: kernel NULL pointer dereference, address: 0000000000000000
>>>>> ...
>>>>> [   24.003992] RIP: 0010:xhci_hub_control+0x3f5/0x60d0 [xhci_hcd]
>>>>> ...
>>>>> [   24.009803] Call Trace:
>>>>> [   24.010014]  <TASK>
>>>>> [   24.011310]  usb_hcd_submit_urb+0x1233/0x1fd0
>>>>> [   24.017071]  usb_start_wait_urb+0x115/0x310
>>>>> [   24.017641]  usb_control_msg+0x28a/0x450
>>>>> [   24.019046]  hub_probe+0xb16/0x2320
>>>>> [   24.019757]  usb_probe_interface+0x4f1/0x930
>>>>> [   24.019765]  really_probe+0x33d/0x970
>>>>> [   24.019768]  __driver_probe_device+0x157/0x210
>>>>> [   24.019772]  driver_probe_device+0x4f/0x340
>>>>> [   24.019775]  __device_attach_driver+0x2ee/0x3a0
>>>>> ...
>>>>>
>>>>> Reported-by: TOTE Robot <oslab@tsinghua.edu.cn>
>>>>> Signed-off-by: Zixuan Fu <r33s3n6@gmail.com>
>>>>> ---
>>>>>  drivers/usb/host/xhci-mem.c | 17 ++++++++++++-----
>>>>>  1 file changed, 12 insertions(+), 5 deletions(-)
>>>>>
>>>>> diff --git a/drivers/usb/host/xhci-mem.c b/drivers/usb/host/xhci-mem.c
>>>>> index bbb27ee2c6a3..024515346c39 100644
>>>>> --- a/drivers/usb/host/xhci-mem.c
>>>>> +++ b/drivers/usb/host/xhci-mem.c
>>>>> @@ -2235,7 +2235,7 @@ static void xhci_add_in_port(struct xhci_hcd *xhci, unsigned int num_ports,
>>>>>       /* FIXME: Should we disable ports not in the Extended Capabilities? */
>>>>>  }
>>>>>
>>>>> -static void xhci_create_rhub_port_array(struct xhci_hcd *xhci,
>>>>> +static int xhci_create_rhub_port_array(struct xhci_hcd *xhci,
>>>>>                                       struct xhci_hub *rhub, gfp_t flags)
>>>>>  {
>>>>>       int port_index = 0;
>>>>> @@ -2243,11 +2243,11 @@ static void xhci_create_rhub_port_array(struct xhci_hcd *xhci,
>>>>>       struct device *dev = xhci_to_hcd(xhci)->self.sysdev;
>>>>>
>>>>>       if (!rhub->num_ports)
>>>>> -             return;
>>>>> +             return -EINVAL;
>>>>>       rhub->ports = kcalloc_node(rhub->num_ports, sizeof(*rhub->ports),
>>>>>                       flags, dev_to_node(dev));
>>>>>       if (!rhub->ports)
>>>>> -             return;
>>>>> +             return -ENOMEM;
>>>>>
>>>>>       for (i = 0; i < HCS_MAX_PORTS(xhci->hcs_params1); i++) {
>>>>>               if (xhci->hw_ports[i].rhub != rhub ||
>>>>> @@ -2259,6 +2259,7 @@ static void xhci_create_rhub_port_array(struct xhci_hcd *xhci,
>>>>>               if (port_index == rhub->num_ports)
>>>>>                       break;
>>>>>       }
>>>>> +     return 0;
>>>>>  }
>>>>>
>>>>>  /*
>>>>> @@ -2277,6 +2278,7 @@ static int xhci_setup_port_arrays(struct xhci_hcd *xhci, gfp_t flags)
>>>>>       int cap_count = 0;
>>>>>       u32 cap_start;
>>>>>       struct device *dev = xhci_to_hcd(xhci)->self.sysdev;
>>>>> +     int ret;
>>>>>
>>>>>       num_ports = HCS_MAX_PORTS(xhci->hcs_params1);
>>>>>       xhci->hw_ports = kcalloc_node(num_ports, sizeof(*xhci->hw_ports),
>>>>> @@ -2367,8 +2369,13 @@ static int xhci_setup_port_arrays(struct xhci_hcd *xhci, gfp_t flags)
>>>>>        * Not sure how the USB core will handle a hub with no ports...
>>>>>        */
>>>>>
>>>>> -     xhci_create_rhub_port_array(xhci, &xhci->usb2_rhub, flags);
>>>>> -     xhci_create_rhub_port_array(xhci, &xhci->usb3_rhub, flags);
>>>>> +     ret = xhci_create_rhub_port_array(xhci, &xhci->usb2_rhub, flags);
>>>>> +     if (ret)
>>>>> +             return ret;
>>>>> +
>>>>> +     ret = xhci_create_rhub_port_array(xhci, &xhci->usb3_rhub, flags);
>>>>> +     if (ret)
>>>>> +             return ret;
>>>>
>>>> What about the memory allocated by the first call to
>>>> xhci_create_rhub_port_array()?  Is that now lost?  Same for everything
>>>> else allocated before these calls, how is that cleaned up properly?
>>>>
>>>> thanks,
>>>>
>>>> greg k-h
>>>
>>> Thanks for your swift reply. We understand your concern. In fact, we have
>>> checked the related code carefully and found that xhci_create_rhub_port_array()
>>> is only used in xhci_setup_port_arrays(). Moreover, only xhci_mem_init() calls
>>> xhci_setup_port_arrays() and does all cleanup work when it fails. Specifically,
>>> xhci_mem_init() calls xhci_mem_cleanup(), which eventually called
>>> kfree(xhci->usb2_rhub.ports) and kfree(xhci->usb3_rhub.ports).
>>
>> Great, can you mention this in the changelog text to show that you have
>> thought this through and it can be documented as such?
>>
>> thanks,
>>
>> greg k-h
> 
> Thanks for your reply! We will do that and submit the patch v2 soon.
> 

Good to get this fixed, but there's a series by Heiner Kallweit that adds support
for xHC controllers with just one roothub [1].
It will conflict with this.  

We might need to change this a bit so that this can go to stable alone, but still
being being able to somewhat neatly apply that new series on top of this.

1. https://git.kernel.org/pub/scm/linux/kernel/git/mnyman/xhci.git/log/?h=for-usb-next

Thanks
-Mathias