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

[Alan Stern]

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);