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

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Message-ID: <tencent_89BAE8BB0933D89E1D1BD94B891BBD257208@qq.com>
Date: Sun, 25 Aug 2024 18:09:45 +0800
From: Edward Adam Davis <eadavis@...com>
To: gregkh@...uxfoundation.org
Cc: eadavis@...com,
	kvalo@...nel.org,
	linux-kernel@...r.kernel.org,
	linux-usb@...r.kernel.org,
	linux-wireless@...r.kernel.org,
	netdev@...r.kernel.org,
	syzbot+92c6dd14aaa230be6855@...kaller.appspotmail.com,
	syzkaller-bugs@...glegroups.com
Subject: Re: [PATCH] wifi: ath6kl: Check that the read operation returns a data length of 0

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: syzbot+92c6dd14aaa230be6855@...kaller.appspotmail.com
> > > > Signed-off-by: Edward Adam Davis <eadavis@...com>
> > > > ---
> > > >  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. 

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

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.
> 
> > +       /* There are two types of read failure situations that need to be captured:
> > +        * 1. short read: ret < size && ret >= 0
> > +        * 2. long read: ret > size
> > +        * */
> > +       if (req == ATH6KL_USB_CONTROL_REQ_RECV_BMI_RESP && ret != size) {
> > +               ath6kl_warn("Actual read the data length is: %d, but input size is %d\n", ret, size);
> > +               return -EIO;
> > +       }
> 
> If you switch to usb_control_msg_send() this logic gets a lot simpler.
> Perhaps do that instead?
> 
> If not, then you need to check for "short writes" or zero writes, see
> the documentation for usb_control_msg() for what it returns.  Your
> comment is not correct here, there are 3 different return "states" that
> you need to handle.
> 
> And why are you caring about what the req type is?

BR,
Edward