Bluetooth: Fix L2CAP command reject reason

There are several possible reason codes that can be sent in the command
reject L2CAP packet. Before this patch the code has used a hard-coded
single response code ("command not understood"). This patch adds a
helper function to map the return value of an L2CAP handler function to
the correct command reject reason.
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>

net/bluetooth/l2cap_core.c

@@ -5294,6 +5294,20 @@ static inline int l2cap_le_sig_cmd(struct l2cap_conn *conn,
 	}
 }
 
+static __le16 l2cap_err_to_reason(int err)
+{
+	switch (err) {
+	case -EBADSLT:
+		return __constant_cpu_to_le16(L2CAP_REJ_INVALID_CID);
+	case -EMSGSIZE:
+		return __constant_cpu_to_le16(L2CAP_REJ_MTU_EXCEEDED);
+	case -EINVAL:
+	case -EPROTO:
+	default:
+		return __constant_cpu_to_le16(L2CAP_REJ_NOT_UNDERSTOOD);
+	}
+}
+
 static inline void l2cap_le_sig_channel(struct l2cap_conn *conn,
 					struct sk_buff *skb)
 {
@@ -5326,8 +5340,7 @@ static inline void l2cap_le_sig_channel(struct l2cap_conn *conn,
 
 			BT_ERR("Wrong link type (%d)", err);
 
-			/* FIXME: Map err to a valid reason */
-			rej.reason = __constant_cpu_to_le16(L2CAP_REJ_NOT_UNDERSTOOD);
+			rej.reason = l2cap_err_to_reason(err);
 			l2cap_send_cmd(conn, cmd.ident, L2CAP_COMMAND_REJ,
 				       sizeof(rej), &rej);
 		}
@@ -5371,8 +5384,7 @@ static inline void l2cap_sig_channel(struct l2cap_conn *conn,
 
 			BT_ERR("Wrong link type (%d)", err);
 
-			/* FIXME: Map err to a valid reason */
-			rej.reason = __constant_cpu_to_le16(L2CAP_REJ_NOT_UNDERSTOOD);
+			rej.reason = l2cap_err_to_reason(err);
 			l2cap_send_cmd(conn, cmd.ident, L2CAP_COMMAND_REJ,
 				       sizeof(rej), &rej);
 		}