[PATCH] HID: cp2112: prevent a buffer overflow in cp2112_xfer()

[Harshit Mogalapalli <harshit.m.mogalapalli@oracle.com>]

Smatch warnings:
drivers/hid/hid-cp2112.c:793 cp2112_xfer() error: __memcpy()
'data->block[1]' too small (33 vs 255)
drivers/hid/hid-cp2112.c:793 cp2112_xfer() error: __memcpy() 'buf' too
small (64 vs 255)

The 'read_length' variable is provided by 'data->block[0]' which comes
from user and it(read_length) can take a value between 0-255. Add an
upper bound to 'read_length' variable to prevent a buffer overflow in
memcpy().

Fixes: 542134c0375b ("HID: cp2112: Fix I2C_BLOCK_DATA transactions")
Signed-off-by: Harshit Mogalapalli <harshit.m.mogalapalli@oracle.com>
---
 drivers/hid/hid-cp2112.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/hid/hid-cp2112.c b/drivers/hid/hid-cp2112.c
index ece147d1a278..1e16b0fa310d 100644
--- a/drivers/hid/hid-cp2112.c
+++ b/drivers/hid/hid-cp2112.c
@@ -790,6 +790,11 @@ static int cp2112_xfer(struct i2c_adapter *adap, u16 addr,
 		data->word = le16_to_cpup((__le16 *)buf);
 		break;
 	case I2C_SMBUS_I2C_BLOCK_DATA:
+		if (read_length > I2C_SMBUS_BLOCK_MAX) {
+			ret = -EINVAL;
+			goto power_normal;
+		}
+
 		memcpy(data->block + 1, buf, read_length);
 		break;
 	case I2C_SMBUS_BLOCK_DATA:
-- 
2.31.1