[PATCH] HID: i2c-hid: fix potential buffer overflow in i2c_hid_get_report()

[Kwok Kin Ming]

`i2c_hid_xfer` is used to read `recv_len + sizeof(__le16)` bytes of data
into `ihid->rawbuf`.

The former can come from the userspace in the hidraw driver and is only
bounded by HID_MAX_BUFFER_SIZE(16384) by default (unless we also set
`max_buffer_size` field of `struct hid_ll_driver` which we do not).

The latter has size determined at runtime by the maximum size of
different report types you could receive on any particular device and
can be a much smaller value.

Fix this by truncating `recv_len` to `ihid->bufsize - sizeof(__le16)`.

The impact is low since access to hidraw devices requires root.

Signed-off-by: Kwok Kin Ming <kenkinming2002@xxxxxxxxx>
---
 drivers/hid/i2c-hid/i2c-hid-core.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/hid/i2c-hid/i2c-hid-core.c b/drivers/hid/i2c-hid/i2c-hid-core.c
index 63f46a2e5..5a183af3d 100644
--- a/drivers/hid/i2c-hid/i2c-hid-core.c
+++ b/drivers/hid/i2c-hid/i2c-hid-core.c
@@ -286,6 +286,7 @@ static int i2c_hid_get_report(struct i2c_hid *ihid,
 	 * In addition to report data device will supply data length
 	 * in the first 2 bytes of the response, so adjust .
 	 */
+	recv_len = min(recv_len, ihid->bufsize - sizeof(__le16));
 	error = i2c_hid_xfer(ihid, ihid->cmdbuf, length,
 			     ihid->rawbuf, recv_len + sizeof(__le16));
 	if (error) {
-- 
2.52.0