Subject: Re: [PATCH] wifi: ath6kl: Check that the read operation returns a data length of 0

From: Greg KH <[email-masked]>
Date: Sun, 25 Aug 2024 13:25:56 +0200

On Sun, Aug 25, 2024 at 06:09:45PM +0800, Edward Adam Davis wrote:
> On Sun, 25 Aug 2024 10:34:00 +0200, Greg KH wrote:
> > On Sun, Aug 25, 2024 at 04:14:17PM +0800, Edward Adam Davis wrote:
> > > On Sun, 25 Aug 2024 09:25:37 +0200, Greg KH wrote:
> > > > > If the data length returned by the device is 0, the read operation
> > > > > should be considered a failure.
> > > > >
> > > > > Reported-and-tested-by: [email-masked]
> > > > > Signed-off-by: Edward Adam Davis <[email-masked]>
> > > > > ---
> > > > >  drivers/net/wireless/ath/ath6kl/usb.c | 3 +++
> > > > >  1 file changed, 3 insertions(+)
> > > > >
> > > > > diff --git a/drivers/net/wireless/ath/ath6kl/usb.c b/drivers/net/wireless/ath/ath6kl/usb.c
> > > > > index 5220809841a6..2a89bab81b24 100644
> > > > > --- a/drivers/net/wireless/ath/ath6kl/usb.c
> > > > > +++ b/drivers/net/wireless/ath/ath6kl/usb.c
> > > > > @@ -1034,6 +1034,9 @@ static int ath6kl_usb_bmi_read(struct ath6kl *ar, u8 *buf, u32 len)
> > > > >  		ath6kl_err("Unable to read the bmi data from the device: %d\n",
> > > > >  			   ret);
> > > > >  		return ret;
> > > > > +	} else {
> > > > > +		ath6kl_err("Actual read the bmi data length is 0 from the device\n");
> > > > > +		return -EIO;
> > > >
> > > > Close, but not quite there.  ath6kl_usb_submit_ctrl_in() needs to verify
> > > > that the actual amount of data was read that was asked for.  If a short
> > > > read happens (or a long one), then an error needs to propagate out, not
> > > > just 0.  See the "note:" line in that function for what needs to be
> > > > properly checked.
> > > >
> > > > hope this helps,
> > > Thanks for your analysis.
> > > I have carefully read your analysis and I am not sure if the following
> > > understanding is appropriate:
> > > diff --git a/drivers/net/wireless/ath/ath6kl/usb.c b/drivers/net/wireless/ath/ath6kl/usb.c
> > > index 2a89bab81b24..35884316a8c8 100644
> > > --- a/drivers/net/wireless/ath/ath6kl/usb.c
> > > +++ b/drivers/net/wireless/ath/ath6kl/usb.c
> > > @@ -932,6 +932,15 @@ static int ath6kl_usb_submit_ctrl_in(struct ath6kl_usb *ar_usb,
> > >
> > >         kfree(buf);
> > 
> > First off, this should be using usb_control_msg_send() instead of having
> > to roll their own buffer handling, right?
> I couldn't figure it out with what you said. 

Meaning this kfree() should not be needed if you use
usb_control_msg_send() (nor the allocation above it.)

> ath6kl_usb_submit_ctrl_in() is similar to usb_control_msg_send(),
> both calling usb_control_msg() to communicate with USB devices.

Yes, it's close, but not quite the same.

> In the current issue, when executing an ATH6KL_USB_CONTROL_REQ_RECV_BMI_RESP
> read request, the length of the data returned from the device is 0, which
> is different from the expected length of the data to be read, resulting in
> a warning.
> 
> ath6kl_usb_submit_ctrl_in()--->
> 	usb_control_msg()--->
> 		usb_internal_control_msg()
> 
> usb_internal_control_msg() will return the length of the data returned from
> the device, usb_control_msg() return the length too, so in ath6kl_usb_submit_ctrl_in(),
> we can filter out incorrect data lengths by judging the value of ret, such
> as ret != Size situation.

Then just do that type of check for that type of read request in the
code that does that call, not 2-3 layers deeper, no need for making this
more complex than needed.

Try removing both of these functions and just call usb functions
directly.

thanks,

greg k-h