[PATCH] i2c: cp2615: Validate read length before copying

[Triet Hoang <triet.hoang.dev@gmail.com>]

The read_len field comes from the untrusted USB payload, which could
potentially exceed the client's originally requested buffer length or
MAX_I2C_SIZE, allowing an out-of-bounds read and write.

Limit read_len to the maximum size of the response buffer and return
-EPROTO for an invalid response.

Signed-off-by: Triet Hoang <triet.hoang.dev@gmail.com>
---
 drivers/i2c/busses/i2c-cp2615.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/i2c/busses/i2c-cp2615.c b/drivers/i2c/busses/i2c-cp2615.c
index 951de6249834..2c79530da306 100644
--- a/drivers/i2c/busses/i2c-cp2615.c
+++ b/drivers/i2c/busses/i2c-cp2615.c
@@ -136,7 +136,7 @@ cp2615_i2c_send(struct usb_interface *usbif, struct cp2615_i2c_transfer *i2c_w)
 }
 
 static int
-cp2615_i2c_recv(struct usb_interface *usbif, unsigned char tag, void *buf)
+cp2615_i2c_recv(struct usb_interface *usbif, unsigned char tag, void *buf, int len)
 {
 	struct usb_device *usbdev = interface_to_usbdev(usbif);
 	struct cp2615_iop_msg *msg;
@@ -160,6 +160,11 @@ cp2615_i2c_recv(struct usb_interface *usbif, unsigned char tag, void *buf)
 		return -EIO;
 	}
 
+	if (i2c_r->read_len > len || i2c_r->read_len > MAX_I2C_SIZE) {
+		kfree(msg);
+		return -EPROTO;
+	}
+
 	res = cp2615_check_status(i2c_r->status);
 	if (!res)
 		memcpy(buf, &i2c_r->data, i2c_r->read_len);
@@ -236,7 +241,7 @@ cp2615_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)
 		ret = cp2615_i2c_send(usbif, &i2c_w);
 		if (ret)
 			break;
-		ret = cp2615_i2c_recv(usbif, i2c_w.tag, msg->buf);
+		ret = cp2615_i2c_recv(usbif, i2c_w.tag, msg->buf, msg->len);
 	}
 	if (ret < 0)
 		return ret;
-- 
2.53.0