Re: [Qemu-devel] [PATCH] ehci: Ensure that device is not NULL before calling usb_ep_get

[Guenter Roeck <linux@roeck-us.net>]

On Wed, Jul 31, 2019 at 01:08:50PM +0200, Philippe Mathieu-Daudé wrote:
> On 7/30/19 7:45 PM, Guenter Roeck wrote:
> > The following assert is seen once in a while while resetting the
> > Linux kernel.
> > 
> > qemu-system-x86_64: hw/usb/core.c:734: usb_ep_get:
> > 	Assertion `dev != NULL' failed.
> > 
> > The call to usb_ep_get() originates from ehci_execute().
> > Analysis and debugging shows that p->queue->dev can indeed be NULL
> > in this function. Add check for this condition and return an error
> > if it is seen.
> 
> Your patch is not wrong as it corrects your case, but I wonder why we
> get there. This assert seems to have catched a bug.
> 
> Gerd, shouldn't we call usb_packet_cleanup() in ehci_reset() rather than
> ehci_finalize()? Then we shouldn't need this patch.
> 


If you send me an alternate patch, I'll be happy to insert it
into my build to give it some test coverage.

Thanks,
Guenter

> > Signed-off-by: Guenter Roeck <linux@roeck-us.net>
> > ---
> >  hw/usb/hcd-ehci.c | 5 +++++
> >  1 file changed, 5 insertions(+)
> > 
> > diff --git a/hw/usb/hcd-ehci.c b/hw/usb/hcd-ehci.c
> > index 62dab05..c759f3e 100644
> > --- a/hw/usb/hcd-ehci.c
> > +++ b/hw/usb/hcd-ehci.c
> > @@ -1348,6 +1348,11 @@ static int ehci_execute(EHCIPacket *p, const char *action)
> >          return -1;
> >      }
> >  
> > +    if (p->queue->dev == NULL) {
> > +        ehci_trace_guest_bug(p->queue->ehci, "No device attached to queue\n");
> > +        return -1;
> > +    }
> > +
> >      if (get_field(p->qtd.token, QTD_TOKEN_TBYTES) > BUFF_SIZE) {
> >          ehci_trace_guest_bug(p->queue->ehci,
> >                               "guest requested more bytes than allowed");
> >