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    SubjectRe: [PATCH] drivers: usb: host: fix NULL pointer dereferences triggered by unhandled errors in xhci_create_rhub_port_array()
    On Thu, Apr 21, 2022 at 03:52:40PM +0300, Mathias Nyman wrote:
    > 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.

    As this is not anything a normal user will ever hit, it should be redone
    on top of your xhci changes as it's not needed in any stable tree.

    thanks,

    greg k-h

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