On Sat, Oct 10, 2020 at 01:59:32PM +0530, Anant Thazhemadam wrote: > While finding usb endpoints in vmk80xx_find_usb_endpoints(), check if > wMaxPacketSize = 0 for the endpoints found. > > Some devices have isochronous endpoints that have wMaxPacketSize = 0 > (as required by the USB-2 spec). > However, since this doesn't apply here, wMaxPacketSize = 0 can be > considered to be invalid. > > Reported-by: syzbot+009f546aa1370056b1c2@xxxxxxxxxxxxxxxxxxxxxxxxx > Tested-by: syzbot+009f546aa1370056b1c2@xxxxxxxxxxxxxxxxxxxxxxxxx > Signed-off-by: Anant Thazhemadam <anant.thazhemadam@xxxxxxxxx> > --- > Changes in v3: > * Correctly list version information > > Changes in v2: > * Fix coding style issue > > The error (as detected by syzbot) is generated in > vmk80xx_write_packet() (which is called in vmk80xx_reset_device()) when > it tries to assign devpriv->usb_tx_buf[0] = cmd. > > This NULL pointer dereference issue arises because > size = usb_endpoint_maxp(devpriv->ep_tx) = 0. > > This can be traced back to vmk80xx_find_usb_endpoints(), where the usb > endpoints are found, and assigned accordingly. > (For some more insight, in vmk80xx_find_usb_endpoints(), > if one of intf->cur_altsetting->iface_desc->endpoints' desc value = 0, > and consequently this endpoint is assigned to devpriv->ep_tx, > this issue gets triggered.) > > Checking if the wMaxPacketSize of an endpoint is invalid and returning > an error value accordingly, seems to fix the error. > > We could also alternatively perform this checking (if the size is 0 or not) > in vmk80xx_reset_device() itself, but it only seemed like covering up the issue > at that place, rather than fixing it, so I wasn't sure that was any better. > > However, if I'm not wrong, this might end up causing the probe to fail, and I'm > not sure if that's the right thing to do in cases like this, and if it isn't I'd > like some input on what exactly is the required course of action in cases like this. > > drivers/staging/comedi/drivers/vmk80xx.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/drivers/staging/comedi/drivers/vmk80xx.c b/drivers/staging/comedi/drivers/vmk80xx.c > index 65dc6c51037e..cb0a965d3c37 100644 > --- a/drivers/staging/comedi/drivers/vmk80xx.c > +++ b/drivers/staging/comedi/drivers/vmk80xx.c > @@ -667,6 +667,9 @@ static int vmk80xx_find_usb_endpoints(struct comedi_device *dev) > if (!devpriv->ep_rx || !devpriv->ep_tx) > return -ENODEV; > > + if (!usb_endpoint_maxp(devpriv->ep_rx) || !usb_endpoint_maxp(devpriv->ep_tx)) > + return -EINVAL; > + > return 0; > } Why not just rewrite vmk80xx_find_usb_endpoints() to use the usb_find_common_endpoints() or other helper functions like usb_find_bulk_in_endpoint() or others, so that this type of thing is checked there? Ah, wait, no, the packet size is not checked there, sorry, maybe that will not help out here. Is a bulk urb allowed to have a 0 size? If not, maybe we should just forbid that in the core? Time to go read the USB spec... thanks, greg k-h _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
