i2c: ismt: Fix an out-of-bounds bug in ismt_access()

When the driver does not check the data from the user, the variable
'data->block[0]' may be very large to cause an out-of-bounds bug.

The following log can reveal it:

[   33.995542] i2c i2c-1: ioctl, cmd=0x720, arg=0x7ffcb3dc3a20
[   33.995978] ismt_smbus 0000:00:05.0: I2C_SMBUS_BLOCK_DATA:  WRITE
[   33.996475] ==================================================================
[   33.996995] BUG: KASAN: out-of-bounds in ismt_access.cold+0x374/0x214b
[   33.997473] Read of size 18446744073709551615 at addr ffff88810efcfdb1 by task ismt_poc/485
[   33.999450] Call Trace:
[   34.001849]  memcpy+0x20/0x60
[   34.002077]  ismt_access.cold+0x374/0x214b
[   34.003382]  __i2c_smbus_xfer+0x44f/0xfb0
[   34.004007]  i2c_smbus_xfer+0x10a/0x390
[   34.004291]  i2cdev_ioctl_smbus+0x2c8/0x710
[   34.005196]  i2cdev_ioctl+0x5ec/0x74c

Fix this bug by checking the size of 'data->block[0]' first.

Fixes: 13f35ac1 ("i2c: Adding support for Intel iSMT SMBus 2.0 host controller")
Signed-off-by: NZheyu Ma <zheyuma97@gmail.com>
Signed-off-by: NWolfram Sang <wsa@kernel.org>

drivers/i2c/busses/i2c-ismt.c

@@ -509,6 +509,9 @@ static int ismt_access(struct i2c_adapter *adap, u16 addr,
 		if (read_write == I2C_SMBUS_WRITE) {
 			/* Block Write */
 			dev_dbg(dev, "I2C_SMBUS_BLOCK_DATA:  WRITE\n");
+			if (data->block[0] < 1 || data->block[0] > I2C_SMBUS_BLOCK_MAX)
+				return -EINVAL;
+
 			dma_size = data->block[0] + 1;
 			dma_direction = DMA_TO_DEVICE;
 			desc->wr_len_cmd = dma_size;