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
