Re: [PATCH v2 4/4] HID: i2c-hid: fix i2c_hid_get_raw_report count mismatches

Jiri Kosina
2012-12-06T10:01:48Z

On Wed, 5 Dec 2012, Jean Delvare wrote:

> > The previous memcpy implementation relied on the size advertized by the
> > device. There were no guarantees that buf was big enough.
> >
> > Some gymnastic is also required with the +2/-2 to take into account
> > the first 2 bytes of the returned buffer where the total returned
> > length is supplied by the device.
> >
> > Signed-off-by: Benjamin Tissoires <benjamin.tissoires@gmail.com>
> > ---
> > drivers/hid/i2c-hid/i2c-hid.c | 16 ++++++++++++----
> > 1 file changed, 12 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/hid/i2c-hid/i2c-hid.c b/drivers/hid/i2c-hid/i2c-hid.c
> > index c6630d4..ce01d59 100644
> > --- a/drivers/hid/i2c-hid/i2c-hid.c
> > +++ b/drivers/hid/i2c-hid/i2c-hid.c
> > @@ -502,23 +502,31 @@ static int i2c_hid_get_raw_report(struct hid_device *hid,
> > {
> > struct i2c_client *client = hid->driver_data;
> > struct i2c_hid *ihid = i2c_get_clientdata(client);
> > + size_t ret_count, ask_count;
> > int ret;
> >
> > if (report_type == HID_OUTPUT_REPORT)
> > return -EINVAL;
> >
> > - if (count > ihid->bufsize)
> > - count = ihid->bufsize;
> > + /* +2 bytes to include the size of the reply in the query buffer */
> > + ask_count = min(count + 2, (size_t)ihid->bufsize);
> >
> > ret = i2c_hid_get_report(client,
> > report_type == HID_FEATURE_REPORT ? 0x03 : 0x01,
> > - report_number, ihid->inbuf, count);
> > + report_number, ihid->inbuf, ask_count);
> >
> > if (ret < 0)
> > return ret;
> >
> > - count = ihid->inbuf[0] | (ihid->inbuf[1] << 8);
> > + ret_count = ihid->inbuf[0] | (ihid->inbuf[1] << 8);
> >
> > + if (!ret_count)
>
> I'd make this (ret_count <= 2), as this would let you call memcpy with a
> null or even negative length.

Good catch, it doesn't account for the 2 bytes needed for storing the
reply size.

I have fixed that and applied the patch, thanks everybody!

--
Jiri Kosina
SUSE Labs