[PATCH] 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 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 32
or return EINVAL

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 | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/drivers/hid/hid-cp2112.c b/drivers/hid/hid-cp2112.c
index 482f62a78c41..90292ce3d363 100644
--- a/drivers/hid/hid-cp2112.c
+++ b/drivers/hid/hid-cp2112.c
@@ -689,7 +689,10 @@ 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,
+			if (data->block[0] > 32)
+				count = -EINVAL;
+			else
+				count = cp2112_write_req(buf, addr, command,
 						 data->block + 1,
 						 data->block[0]);
 		}
@@ -700,7 +703,10 @@ 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,
+			if (data->block[0] > 32)
+				count = -EINVAL;
+			else
+				count = cp2112_write_req(buf, addr, command,
 						 data->block,
 						 data->block[0] + 1);
 		}
@@ -709,7 +715,10 @@ 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,
+		if (data->block[0] > 32)
+			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