Re: [syzbot] [usb?] WARNING in dib0700_i2c_xfer/usb_submit_urb

Alan Stern
2025-03-25T17:47:19Z

On Tue, Mar 25, 2025 at 05:59:10PM +0100, Wolfram Sang wrote:
>
> > > > As far as I can tell from the source code, the dib0700 simply isn't able
> > > > to handle 0-length reads. Should the dib0700_ctrl_rd() routine be
> > > > changed simply to return 0 in such cases?
> > >
> > > The adapter (I assume the one in dvb-usb-i2c.c) should populate an
> > > i2c_adapter_quirks struct with I2C_AQ_NO_ZERO_LEN and then the core will
> > > bail out for you.
> >
> > Or the I2C_AQ_NO_ZERO_LEN_READ flag bit.
>
> Yes, that would be more convervative. Does USB allow zero-length writes?

It does.

> > What about all the other fields in the i2c_adapter_quirks structure?
> > How should they be set? (Note: I don't know anything about this driver
> > or these devices; I'm just chasing down the syzbot bug report.)
>
> As I also don't know the hardware, I suggest to leave them empty. 0
> means "no quirk".

Okay, let's see if this works.

Alan Stern

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git 5fc319360819

Index: usb-devel/drivers/media/usb/dvb-usb/dvb-usb-i2c.c
===================================================================
--- usb-devel.orig/drivers/media/usb/dvb-usb/dvb-usb-i2c.c
+++ usb-devel/drivers/media/usb/dvb-usb/dvb-usb-i2c.c
@@ -10,6 +10,9 @@

int dvb_usb_i2c_init(struct dvb_usb_device *d)
{
+ static const struct i2c_adapter_quirks i2c_usb_quirks = {
+ .flags = I2C_AQ_NO_ZERO_LEN_READ,
+ };
int ret = 0;

if (!(d->props.caps & DVB_USB_IS_AN_I2C_ADAPTER))
@@ -24,6 +27,7 @@ int dvb_usb_i2c_init(struct dvb_usb_devi
strscpy(d->i2c_adap.name, d->desc->name, sizeof(d->i2c_adap.name));
d->i2c_adap.algo = d->props.i2c_algo;
d->i2c_adap.algo_data = NULL;
+ d->i2c_adap.quirks = &i2c_usb_quirks;
d->i2c_adap.dev.parent = &d->udev->dev;

i2c_set_adapdata(&d->i2c_adap, d);