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SubjectRe: [PATCH v2] usb:host: fix divide-by-zero in function fhci_queue_urb
On Wed, 17 Apr 2019, zhuyan (M) wrote:

> On Wed, 17 Apr 2019, Alan Stern wrote:
>
> > On Wed, 17 Apr 2019, zhuyan (M) wrote:
> >
> > > On Tue, 16 Apr 2019 11:07:56 -0400, Alan Stern wrote:
> > >
> > > > On Tue, 16 Apr 2019, zhuyan (M) wrote:
> > > > > On Tue, 16 Apr 2019 at 11:45:45 +0200, Greg KH wrote:
> > > > > > On Tue, Apr 09, 2019 at 10:37:12PM +0800, zhuyan wrote:
> > > > > > > In function fhci_queue_urb, the divisor of expression
> > > > > > > (urb->transfer_buffer_length % usb_maxpacket(urb->dev,
> > > > > > > urb->pipe,
> > > > > > > usb_pipeout(urb->pipe))) may be zero.
> > > > > >
> > > > > > How can you hit that?
> > > > > >
> > > > > > > When it is zero, unexpected results may occur, so it is
> > > > > > > necessary to ensure that the divisor is not zero.
> > > > > > >
> > > > > > > Signed-off-by: zhuyan <zhuyan34@huawei.com>
> > > > > >
> > > > > > I need a "Full" name here, not just a single name. Whatever you use to sign documents is good.
> > > > > >
> > > > > > thanks,
> > > > > >
> > > > > > greg k-h
> > > > >
> > > > > In function usb_maxpacket, when ep is NULL, its return value is 0.
> > > >
> > > > fhci_queue_urb() shouldn't use urb->pipe to compute the maxpacket
> > > > size anyway. It should use usb_endpoint_maxp(&urb->ep->desc).
> > >
> > > Currently, fhci_queue_urb(), call usb_maxpacket() multiple times to
> > > calculate the maxpacket size. The usb_maxpacket() will call
> > > usb_endpoint_maxp() to compute the maxpacket size.
> >
> > I know that. What fhci_queue_urb() is doing is wrong. You should change it:
> > Make it call usb_endpoint_maxp directly instead of calling usb_maxpacket.
> >
>
> From 1996456d0cc17b5ff7746a598ff355b25d13db3e Mon Sep 17 00:00:00 2001
> From: zhuyan <zhuyan34@huawei.com>
> Date: Thu, 18 Apr 2019 00:53:03 +0800
> Subject: [PATCH] usb: host: fix divide-by-zero in function fhci_queue_urb
>
> fhci_queue_urb() shouldn't use urb->pipe to compute the maxpacket
> size anyway.It should use usb_endpoint_maxp(&urb->ep->desc).
>
> In function fhci_queue_urb, the divisor of expression
> (urb->transfer_buffer_length % usb_maxpacket(urb->dev, urb->pipe,
> usb_pipeout(urb->pipe))) may be zero. When it is zero, unexpected results
> may occur, so it is necessary to ensure that the divisor is not zero.
>
> Signed-off-by: zhuyan <zhuyan34@huawei.com>
> ---
> drivers/usb/host/fhci-sched.c | 13 +++++++------
> 1 file changed, 7 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/usb/host/fhci-sched.c b/drivers/usb/host/fhci-sched.c
> index 3d12cdd..7dcfe22 100644
> --- a/drivers/usb/host/fhci-sched.c
> +++ b/drivers/usb/host/fhci-sched.c
> @@ -704,6 +704,7 @@ void fhci_queue_urb(struct fhci_hcd *fhci, struct urb *urb)
> struct td *td;
> u8 *data;
> u16 cnt = 0;
> + u16 max_pkt_size = 0;
>
> if (ed == NULL) {
> ed = fhci_get_empty_ed(fhci);
> @@ -727,8 +728,7 @@ void fhci_queue_urb(struct fhci_hcd *fhci, struct urb *urb)
> }
> ed->speed = (urb->dev->speed == USB_SPEED_LOW) ?
> FHCI_LOW_SPEED : FHCI_FULL_SPEED;
> - ed->max_pkt_size = usb_maxpacket(urb->dev,
> - urb->pipe, usb_pipeout(urb->pipe));
> + ed->max_pkt_size = usb_endpoint_maxp(&urb->ep->desc);
> urb->ep->hcpriv = ed;
> fhci_dbg(fhci, "new ep speed=%d max_pkt_size=%d\n",
> ed->speed, ed->max_pkt_size);
> @@ -765,11 +765,12 @@ void fhci_queue_urb(struct fhci_hcd *fhci, struct urb *urb)
>
> switch (ed->mode) {
> case FHCI_TF_BULK:
> + max_pkt_size = usb_endpoint_maxp(&urb->ep->desc);
> if (urb->transfer_flags & URB_ZERO_PACKET &&
> urb->transfer_buffer_length > 0 &&
> + (max_pkt_size != 0) &&

Now you shouldn't need to add this extra test.

Alan Stern

> ((urb->transfer_buffer_length %
> - usb_maxpacket(urb->dev, urb->pipe,
> - usb_pipeout(urb->pipe))) == 0))
> + max_pkt_size) == 0))
> urb_state = US_BULK0;
> while (data_len > 4096) {
> td = fhci_td_fill(fhci, urb, urb_priv, ed, cnt,
> @@ -807,8 +808,8 @@ void fhci_queue_urb(struct fhci_hcd *fhci, struct urb *urb)
> break;
> case FHCI_TF_CTRL:
> ed->dev_addr = usb_pipedevice(urb->pipe);
> - ed->max_pkt_size = usb_maxpacket(urb->dev, urb->pipe,
> - usb_pipeout(urb->pipe));
> + ed->max_pkt_size = usb_endpoint_maxp(&urb->ep->desc);
> +
> /* setup stage */
> td = fhci_td_fill(fhci, urb, urb_priv, ed, cnt++, FHCI_TA_SETUP,
> USB_TD_TOGGLE_DATA0, urb->setup_packet, 8, 0, 0, true);

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