Re: [RFC PATCH] usb: dwc3: ep0: Fix mem corruption on OUT transfers of more than 512 bytes

From: Felipe Balbi
Date: Tue Jun 09 2015 - 13:19:23 EST


On Tue, Jun 09, 2015 at 10:59:50AM -0400, Alan Stern wrote:
> On Tue, 9 Jun 2015, Kishon Vijay Abraham I wrote:
>
> > Hi,
> >
> > On Tuesday 09 June 2015 08:09 PM, Michael Trimarchi wrote:
> > > Hi
> > >
> > > On Jun 9, 2015 4:36 PM, "Kishon Vijay Abraham I" <kishon@xxxxxx
> > > <mailto:kishon@xxxxxx>> wrote:
> > > >
> > > > DWC3 uses bounce buffer to handle non max packet aligned OUT transfers and
> > > > the size of bounce buffer is 512 bytes. However if the host initiates OUT
> > > > transfers of size more than 512 bytes (and non max packet aligned), the
> > > > driver throws a WARN dump but still programs the TRB to receive more than
> > > > 512 bytes. This will cause bounce buffer to overflow and corrupt the
> > > > adjacent memory locations which can be fatal.
> > > >
> > > > Fix it by programming the TRB to receive a maximum of DWC3_EP0_BOUNCE_SIZE
> > > > (512) bytes.
> > > >
> > > > Signed-off-by: Kishon Vijay Abraham I <kishon@xxxxxx <mailto:kishon@xxxxxx>>
> > > > ---
> > > > Steps to see the issue (before this patch)
> > > > 1) Insert g_zero in DUT
> > > > 2) run './testusb -t 14 -c 1 -s 520 -v 1' in host (size should be > 512)
> > > >
> > > > The test should FAIL since bounce buffer can handle only 512 bytes, but the
> > > > test PASS. There is a WARN dump in DUT but still there will be memory
> > > > corruption since the bounce buffer overflows.
> > > >
> > > > Tested this patch using USB3 Gen X CV (ch9 tests: usb2 and usb3, link layer
> > > > testing and MSC tests) and using USB2 X CV (ch9 tests, MSC tests).
> > > >
> > > > After the patch, the tests timeout!
> > > > ./testusb -t 14 -c 1 -s 514 -v 1
> > > > unknown speed /dev/bus/usb/001/018 0
> > > > /dev/bus/usb/001/018 test 14 --> 110 (Connection timed out)
> > > >
> > > > IMO a patch to fix this is required for stable releases too. So If this
> > > > patch is alright, I can post the patch cc'ing stable. While the actual fix
> > > > would be to have chained TRB, I'm not sure if it can go to stable
> > > > releases.
> > > > drivers/usb/dwc3/ep0.c | 12 ++++++++++--
> > > > 1 file changed, 10 insertions(+), 2 deletions(-)
> > > >
> > > > diff --git a/drivers/usb/dwc3/ep0.c b/drivers/usb/dwc3/ep0.c
> > > > index 2ef3c8d..8858c60 100644
> > > > --- a/drivers/usb/dwc3/ep0.c
> > > > +++ b/drivers/usb/dwc3/ep0.c
> > > > @@ -816,6 +816,11 @@ static void dwc3_ep0_complete_data(struct dwc3 *dwc,
> > > > unsigned maxp = ep0->endpoint.maxpacket;
> > > >
> > > > transfer_size += (maxp - (transfer_size % maxp));
> > > > +
> > > > + /* Maximum of DWC3_EP0_BOUNCE_SIZE can only be received */
> > > > + if (transfer_size > DWC3_EP0_BOUNCE_SIZE)
> > > > + transfer_size = DWC3_EP0_BOUNCE_SIZE;
> > > > +
> > >
> > > Can you just use maxp in the correct way?
> >
> > what do you mean by correct way? Using roundup() to calculate transfer_size?
>
> Why not just make the bounce buffer size the same as the maxpacket
> size? In other words, 1024 bytes instead of 512, for ep0 on a USB-3
> device.

EP0 max packet size is 512 on USB3.

--
balbi

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