Re: [bug report] HID: ft260: add usb hid to i2c host bridge driver

[Dan Carpenter <dan.carpenter@oracle.com>]

On Sun, Apr 11, 2021 at 12:04:25AM +0300, Michael Zaidman wrote:
> On Sat, Apr 10, 2021 at 06:37:13PM +0300, Dan Carpenter wrote:
> > On Sat, Apr 10, 2021 at 03:27:29PM +0300, Michael Zaidman wrote:
> > > On Fri, Apr 09, 2021 at 03:32:06PM +0300, Dan Carpenter wrote:
> > > > Hello Michael Zaidman,
> > > > 
> > > > The patch 6a82582d9fa4: "HID: ft260: add usb hid to i2c host bridge
> > > > driver" from Feb 19, 2021, leads to the following static checker
> > > > warning:
> > > > 
> > > > 	drivers/hid/hid-ft260.c:441 ft260_smbus_write()
> > > > 	error: '__memcpy()' '&rep->data[1]' too small (59 vs 255)
> > > > 
> > > > drivers/hid/hid-ft260.c
> > > >    423  static int ft260_smbus_write(struct ft260_device *dev, u8 addr, u8 cmd,
> > > >    424                               u8 *data, u8 data_len, u8 flag)
> > > >    425  {
> > > >    426          int ret = 0;
> > > >    427          int len = 4;
> > > >    428  
> > > >    429          struct ft260_i2c_write_request_report *rep =
> > > >    430                  (struct ft260_i2c_write_request_report *)dev->write_buf;
> > > >    431  
> > > >    432          rep->address = addr;
> > > >    433          rep->data[0] = cmd;
> > > >    434          rep->length = data_len + 1;
> > > >    435          rep->flag = flag;
> > > >    436          len += rep->length;
> > > >    437  
> > > >    438          rep->report = FT260_I2C_DATA_REPORT_ID(len);
> > > >    439  
> > > >    440          if (data_len > 0)
> > > >    441                  memcpy(&rep->data[1], data, data_len);
> > > >                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> > > > Smatch says that this can be called from the i2cdev_ioctl_smbus()
> > > > function.
> > > 
> > > Hi Dan,
> > > 
> > > This is an example of a false-positive static checker warning.
> > > 
> > > The maximum data size that the i2cdev_ioctl_smbus() can pass to the
> > > i2c_smbus_xfer() is sizeof(data->block) which is (I2C_SMBUS_BLOCK_MAX + 2)
> > > or 34 bytes. Thus, no need to check the data_len against 59 here.
> > > 
> > > > 
> > > > i2cdev_ioctl_smbus()
> > > >   --> i2c_smbus_xfer
> > > >       --> __i2c_smbus_xfer
> > > >           --> ft260_smbus_xfer
> > > >               --> ft260_smbus_write
> > 
> > It's actually me who misunderstood the Smatch warning.  Smatch is not
> > complaining about data_len, it's data->block[0] which is user
> > controlled and only for the I2C_SMBUS_I2C_BLOCK_DATA command.
> > 
> > The call tree is the same.  I've looked at it again.  Here is how
> > i2cdev_ioctl_smbus() looks like:
> > 
> > drivers/i2c/i2c-dev.c
> >    355                  return -EINVAL;
> >    356          }
> >    357  
> >    358          if ((size == I2C_SMBUS_BYTE_DATA) ||
> >    359              (size == I2C_SMBUS_BYTE))
> >    360                  datasize = sizeof(data->byte);
> >    361          else if ((size == I2C_SMBUS_WORD_DATA) ||
> >    362                   (size == I2C_SMBUS_PROC_CALL))
> >    363                  datasize = sizeof(data->word);
> >    364          else /* size == smbus block, i2c block, or block proc. call */
> >    365                  datasize = sizeof(data->block);
> >                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> > 
> >    366  
> >    367          if ((size == I2C_SMBUS_PROC_CALL) ||
> >    368              (size == I2C_SMBUS_BLOCK_PROC_CALL) ||
> >    369              (size == I2C_SMBUS_I2C_BLOCK_DATA) ||
> >                              ^^^^^^^^^^^^^^^^^^^^^^^^
> >    370              (read_write == I2C_SMBUS_WRITE)) {
> >    371                  if (copy_from_user(&temp, data, datasize))
> >                                             ^^^^
> > temp.block[0] is user controlled.
> > 
> >    372                          return -EFAULT;
> >    373          }
> >    374          if (size == I2C_SMBUS_I2C_BLOCK_BROKEN) {
> >                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> > 
> >    375                  /* Convert old I2C block commands to the new
> >    376                     convention. This preserves binary compatibility. */
> >    377                  size = I2C_SMBUS_I2C_BLOCK_DATA;
> >    378                  if (read_write == I2C_SMBUS_READ)
> >    379                          temp.block[0] = I2C_SMBUS_BLOCK_MAX;
> >                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> > Except for size BROKEN
> > 
> >    380          }
> >    381          res = i2c_smbus_xfer(client->adapter, client->addr, client->flags,
> >    382                read_write, command, size, &temp);
> >                                                  ^^^^^
> > 
> >    383          if (!res && ((size == I2C_SMBUS_PROC_CALL) ||
> >    384                       (size == I2C_SMBUS_BLOCK_PROC_CALL) ||
> >    385                       (read_write == I2C_SMBUS_READ))) {
> >    386                  if (copy_to_user(data, &temp, datasize))
> >    387                          return -EFAULT;
> >    388          }
> > 
> > The rest of the call tree seems straight forward but it's possible I
> > have missed somewhere that checks data[0].  Here is how ft260_smbus_xfer()
> > looks like.
> 
> Oh, you are right. Despite that the SMbus block transaction limits the maximum
> number of bytes to 32, nothing prevents a user from specifying via ioctl a larger
> data size than the ft260 can handle in a single transfer.
> 
> I am going to fix it in the ft260_smbus_write (with your Signed-off-by), but
> perhaps we should fix it in the first place, in the i2cdev_ioctl_smbus routine?
> What do you think?

Could you just give me a Reported-by tag?  Thanks!

regards,
dan carpenter