[PATCH v2] HID: cp2112: Add parameter validation to data length

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

This is v2 for the earlier patch, where a few bounds check were
unnecessarily strict. This patch also removes the use of magic numbers

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

I2C device drivers are "responsible for checking all the parameters that
come from user-space for validity" as specified at Documentation/i2c/dev-interface

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
Signed-off-by: Deepak Sharma <deepak.sharma.472935@gmail.com>
---
 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