Bluetooth: Fix incorrect strncpy() in hidp_setup_hid()

commit 0a9ab9bd upstream.

The length parameter should be sizeof(req->name) - 1 because there is no
guarantee that string provided by userspace will contain the trailing
'\0'.

Can be easily reproduced by manually setting req->name to 128 non-zero
bytes prior to ioctl(HIDPCONNADD) and checking the device name setup on
input subsystem:

$ cat /sys/devices/pnp0/00\:04/tty/ttyS0/hci0/hci0\:1/input8/name
AAAAAA[...]AAAAAAAAf0:af:f0:af:f0:af

("f0:af:f0:af:f0:af" is the device bluetooth address, taken from "phys"
field in struct hid_device due to overflow.)
Signed-off-by: Anderson Lizardo <anderson.lizardo@openbossa.org>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

net/bluetooth/hidp/core.c

@@ -945,7 +945,7 @@ static int hidp_setup_hid(struct hidp_session *session,
 	hid->version = req->version;
 	hid->country = req->country;
 
-	strncpy(hid->name, req->name, 128);
+	strncpy(hid->name, req->name, sizeof(req->name) - 1);
 	strncpy(hid->phys, batostr(&bt_sk(session->ctrl_sock->sk)->src), 64);
 	strncpy(hid->uniq, batostr(&bt_sk(session->ctrl_sock->sk)->dst), 64);