Bluetooth: Prevent uninitialized data access in L2CAP configuration

When configuring an ERTM or streaming mode connection, remote devices
are expected to send an RFC option in a successful config response.  A
misbehaving remote device might not send an RFC option, and the L2CAP
code should not access uninitialized data in this case.
Signed-off-by: Mat Martineau <mathewm@codeaurora.org>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Gustavo F. Padovan <padovan@profusion.mobi>

net/bluetooth/l2cap_core.c

@@ -2152,7 +2152,7 @@ static int l2cap_parse_conf_rsp(struct l2cap_chan *chan, void *rsp, int len, voi
 	void *ptr = req->data;
 	int type, olen;
 	unsigned long val;
-	struct l2cap_conf_rfc rfc;
+	struct l2cap_conf_rfc rfc = { .mode = L2CAP_MODE_BASIC };
 
 	BT_DBG("chan %p, rsp %p, len %d, req %p", chan, rsp, len, data);
 
@@ -2271,6 +2271,16 @@ static void l2cap_conf_rfc_get(struct l2cap_chan *chan, void *rsp, int len)
 		}
 	}
 
+	/* Use sane default values in case a misbehaving remote device
+	 * did not send an RFC option.
+	 */
+	rfc.mode = chan->mode;
+	rfc.retrans_timeout = cpu_to_le16(L2CAP_DEFAULT_RETRANS_TO);
+	rfc.monitor_timeout = cpu_to_le16(L2CAP_DEFAULT_MONITOR_TO);
+	rfc.max_pdu_size = cpu_to_le16(chan->imtu);
+
+	BT_ERR("Expected RFC option was not found, using defaults");
+
 done:
 	switch (rfc.mode) {
 	case L2CAP_MODE_ERTM: