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.
drivers/hid/hid-ft260.c
655 case I2C_SMBUS_BLOCK_DATA:
656 if (read_write == I2C_SMBUS_READ) {
657 ret = ft260_smbus_write(dev, addr, cmd, NULL, 0,
658 FT260_FLAG_START);
659 if (ret)
660 goto smbus_exit;
661
662 ret = ft260_i2c_read(dev, addr, data->block,
663 data->block[0] + 1,
664 FT260_FLAG_START_STOP_REPEATED);
665 } else {
666 ret = ft260_smbus_write(dev, addr, cmd, data->block,
667 data->block[0] + 1,
668 FT260_FLAG_START_STOP);
669 }
670 break;
671 case I2C_SMBUS_I2C_BLOCK_DATA:
672 if (read_write == I2C_SMBUS_READ) {
673 ret = ft260_smbus_write(dev, addr, cmd, NULL, 0,
674 FT260_FLAG_START);
675 if (ret)
676 goto smbus_exit;
677
678 ret = ft260_i2c_read(dev, addr, data->block + 1,
679 data->block[0],
680 FT260_FLAG_START_STOP_REPEATED);
681 } else {
682 ret = ft260_smbus_write(dev, addr, cmd, data->block + 1,
683 data->block[0],
^^^^^^^^^^^^^^
Boom. Dead.
684 FT260_FLAG_START_STOP);
685 }
686 break;
687 default:
688 hid_err(hdev, "unsupported smbus transaction size %d\n", size);
689 ret = -EOPNOTSUPP;
690 }
regards,
dan carpenter
