Re: [PATCH] xhci: fix null pointer deref for xhci_urb_enqueue

[Kuen-Han Tsai]

Hi Mathias

>>       if (usb_endpoint_xfer_isoc(&urb->ep->desc))
>> @@ -1552,8 +1561,10 @@ static int xhci_urb_enqueue(struct usb_hcd *hcd, struct urb *urb, gfp_t mem_flag
>>               num_tds = 1;
>>
>>       urb_priv = kzalloc(struct_size(urb_priv, td, num_tds), mem_flags);
> kzalloc with spinlock held, should preferably be moved outside lock, otherwise should use GFP_ATOMIC

Thanks for pointing this out. I realize this patch is incorrect and it
is non-ideal to include many codes unrelated to xhci->devs[slot_id]
within the lock.

> xhci_check_maxpacket() called here can't be called with spinlock held

It appears that xhci_check_maxpacket() might potentially lead to a
deadlock later if a spinlock is held. Is this the concern you were
referring to? If not, please let me know if there are any other
potential issues that I may have missed, thanks!


On Fri, Nov 17, 2023 at 9:31 PM Mathias Nyman
<mathias.nyman@xxxxxxxxxxxxxxx> wrote:
>
> On 17.11.2023 9.21, Kuen-Han Tsai wrote:
> > The null pointer dereference happens when xhci_free_dev() frees the
> > xhci->devs[slot_id] virtual device while xhci_urb_enqueue() is
> > processing a urb and checking the max packet size.
> >
> > [106913.850735][ T2068] usb 2-1: USB disconnect, device number 2
> > [106913.856999][ T4618] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000010
> > [106913.857488][ T4618] Call trace:
> > [106913.857491][ T4618]  xhci_check_maxpacket+0x30/0x2dc
> > [106913.857494][ T4618]  xhci_urb_enqueue+0x24c/0x47c
> > [106913.857498][ T4618]  usb_hcd_submit_urb+0x1f4/0xf34
> > [106913.857501][ T4618]  usb_submit_urb+0x4b8/0x4fc
> > [106913.857503][ T4618]  usb_control_msg+0x144/0x238
> > [106913.857507][ T4618]  do_proc_control+0x1f0/0x5bc
> > [106913.857509][ T4618]  usbdev_ioctl+0xdd8/0x15a8
> >
> > This patch adds a spinlock to the xhci_urb_enqueue function to make sure
> > xhci_free_dev() and xhci_urb_enqueue() do not race and cause null
> > pointer dereference.
>
> Thanks, nice catch
>
> This patch does however need some additional tuning
>
> >
> > Signed-off-by: Kuen-Han Tsai <khtsai@xxxxxxxxxx>
> > ---
> >   drivers/usb/host/xhci.c | 38 ++++++++++++++++++++++++--------------
> >   1 file changed, 24 insertions(+), 14 deletions(-)
> >
> > diff --git a/drivers/usb/host/xhci.c b/drivers/usb/host/xhci.c
> > index 884b0898d9c9..e0766ebeff0e 100644
> > --- a/drivers/usb/host/xhci.c
> > +++ b/drivers/usb/host/xhci.c
> > @@ -1522,23 +1522,32 @@ static int xhci_urb_enqueue(struct usb_hcd *hcd, struct urb *urb, gfp_t mem_flag
> >       struct urb_priv *urb_priv;
> >       int num_tds;
> >
> > -     if (!urb)
> > -             return -EINVAL;
> > -     ret = xhci_check_args(hcd, urb->dev, urb->ep,
> > -                                     true, true, __func__);
> > -     if (ret <= 0)
> > -             return ret ? ret : -EINVAL;
> > +     spin_lock_irqsave(&xhci->lock, flags);
> > +
> > +     if (!urb) {
> > +             ret = -EINVAL;
> > +             goto done;
> > +     }
> > +
> > +     ret = xhci_check_args(hcd, urb->dev, urb->ep, true, true, __func__);
> > +     if (ret <= 0) {
> > +             ret = ret ? ret : -EINVAL;
> > +             goto done;
> > +     }
> >
> >       slot_id = urb->dev->slot_id;
> >       ep_index = xhci_get_endpoint_index(&urb->ep->desc);
> >       ep_state = &xhci->devs[slot_id]->eps[ep_index].ep_state;
> >
> > -     if (!HCD_HW_ACCESSIBLE(hcd))
> > -             return -ESHUTDOWN;
> > +     if (!HCD_HW_ACCESSIBLE(hcd)) {
> > +             ret = -ESHUTDOWN;
> > +             goto done;
> > +     }
> >
> >       if (xhci->devs[slot_id]->flags & VDEV_PORT_ERROR) {
> >               xhci_dbg(xhci, "Can't queue urb, port error, link inactive\n");
> > -             return -ENODEV;
> > +             ret = -ENODEV;
> > +             goto done;
> >       }
> >
> >       if (usb_endpoint_xfer_isoc(&urb->ep->desc))
> > @@ -1552,8 +1561,10 @@ static int xhci_urb_enqueue(struct usb_hcd *hcd, struct urb *urb, gfp_t mem_flag
> >               num_tds = 1;
> >
> >       urb_priv = kzalloc(struct_size(urb_priv, td, num_tds), mem_flags);
>
> kzalloc with spinlock held, should preferably be moved outside lock, otherwise should use GFP_ATOMIC
>
> > -     if (!urb_priv)
> > -             return -ENOMEM;
> > +     if (!urb_priv) {
> > +             ret = -ENOMEM;
> > +             goto done;
> > +     }
> >
> >       urb_priv->num_tds = num_tds;
> >       urb_priv->num_tds_done = 0;
> > @@ -1571,13 +1582,11 @@ static int xhci_urb_enqueue(struct usb_hcd *hcd, struct urb *urb, gfp_t mem_flag
>
> xhci_check_maxpacket() called here can't be called with spinlock held
>
> >                       if (ret < 0) {
> >                               xhci_urb_free_priv(urb_priv);
> >                               urb->hcpriv = NULL;
> > -                             return ret;
> > +                             goto done;
>
> Thanks
> Mathias