[PATCH v3] HID: cp2112: Add parameter validation to data length

[Deepak Sharma <deepak.sharma.472935@gmail.com>]

Syzkaller reported a stack OOB access in cp2112_write_req caused by lack
of parameter validation for the user input in I2C SMBUS ioctl in cp2112
driver

Add the parameter validation for the data->block[0] to be bounded by
I2C_SMBUS_BLOCK_MAX + the additional compatibility padding

Reported-by: syzbot+7617e19c8a59edfbd879@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=7617e19c8a59edfbd879
Tested-by: syzbot+7617e19c8a59edfbd879@syzkaller.appspotmail.com
Signed-off-by: Deepak Sharma <deepak.sharma.472935@gmail.com>
---
v3:
 - Fix the commit message to not include the changelog

v2:
 - Get rid of magic numbers
 - Improve the bounds check

v1:
 - Add bound checks on the input parameters at the driver

 drivers/hid/hid-cp2112.c | 27 ++++++++++++++++++++++++---
 1 file changed, 24 insertions(+), 3 deletions(-)

diff --git a/drivers/hid/hid-cp2112.c b/drivers/hid/hid-cp2112.c
index 482f62a78c41..13dcd2470d92 100644
--- a/drivers/hid/hid-cp2112.c
+++ b/drivers/hid/hid-cp2112.c
@@ -689,7 +689,14 @@ static int cp2112_xfer(struct i2c_adapter *adap, u16 addr,
 			count = cp2112_write_read_req(buf, addr, read_length,
 						      command, NULL, 0);
 		} else {
-			count = cp2112_write_req(buf, addr, command,
+			/* Copy starts from data->block[1] so the length can
+			 * be at max I2C_SMBUS_CLOCK_MAX + 1
+			 */
+			
+			if (data->block[0] > I2C_SMBUS_BLOCK_MAX + 1)
+				count = -EINVAL;
+			else
+				count = cp2112_write_req(buf, addr, command,
 						 data->block + 1,
 						 data->block[0]);
 		}
@@ -700,7 +707,14 @@ static int cp2112_xfer(struct i2c_adapter *adap, u16 addr,
 						      I2C_SMBUS_BLOCK_MAX,
 						      command, NULL, 0);
 		} else {
-			count = cp2112_write_req(buf, addr, command,
+			/* data_length here is data->block[0] + 1
+			 * so make sure that the data->block[0] is
+			 * less than or equals I2C_SMBUS_BLOCK_MAX + 1
+			*/
+			if (data->block[0] > I2C_SMBUS_BLOCK_MAX + 1)
+				count = -EINVAL;
+			else
+				count = cp2112_write_req(buf, addr, command,
 						 data->block,
 						 data->block[0] + 1);
 		}
@@ -709,7 +723,14 @@ static int cp2112_xfer(struct i2c_adapter *adap, u16 addr,
 		size = I2C_SMBUS_BLOCK_DATA;
 		read_write = I2C_SMBUS_READ;
 
-		count = cp2112_write_read_req(buf, addr, I2C_SMBUS_BLOCK_MAX,
+		/* data_length is data->block[0] + 1, so 
+		 * so data->block[0] should be less than or
+		 * equal to the I2C_SMBUS_BLOCK_MAX + 1
+		*/
+		if (data->block[0] > I2C_SMBUS_BLOCK_MAX + 1)
+			count = -EINVAL;
+		else
+			count = cp2112_write_read_req(buf, addr, I2C_SMBUS_BLOCK_MAX,
 					      command, data->block,
 					      data->block[0] + 1);
 		break;
-- 
2.51.0