linux-kernel - [PATCH] Bluetooth: add missing checks in state transitions

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Date: Fri,  9 Feb 2024 02:04:44 -0500
From: Sungwoo Kim <iam@...g-woo.kim>
To: 
Cc: daveti@...due.edu,
	Sungwoo Kim <iam@...g-woo.kim>,
	Marcel Holtmann <marcel@...tmann.org>,
	Johan Hedberg <johan.hedberg@...il.com>,
	Luiz Augusto von Dentz <luiz.dentz@...il.com>,
	linux-bluetooth@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] Bluetooth: add missing checks in state transitions

When an l2cap channel receives L2CAP_CONN_RSP, it revives from BT_DISCONN
to BT_CONFIG or BT_CONNECTED.
It is very weird, violates the specification, and I cannot see any real
usecase for this.
Similar to this, the L2cap channel has six illegal state transitions:

1. BT_CONNECT2 -> BT_CONFIG by L2CAP_CONN_RSP
2. BT_CONNECT2 -> BT_CONNECTED by L2CAP_CONF_RSP
3. BT_CONNECT2 -> BT_DISCONN by L2CAP_CONF_RSP
4. BT_CONNECTED -> BT_CONFIG by L2CAP_CONN_RSP
5. BT_DISCONN -> BT_CONFIG by L2CAP_CONN_RSP
6. BT_DISCONN -> BT_CONNECTED by L2CAP_CONN_RSP

This patch fixes 2, 3, 5, and 6 by adding checks.
For 1 and 4, I will make an RFC for as it requires some refactoring.

The detaild logs are described in here:
https://lore.kernel.org/lkml/CAJNyHpKpDdps4=QHZ77zu4jfY-NNBcGUrw6UwjuBKfpuSuE__g@mail.gmail.com/

Signed-off-by: Sungwoo Kim <iam@...g-woo.kim>
---
 net/bluetooth/l2cap_core.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
index 60298975d..c5fa2b683 100644
--- a/net/bluetooth/l2cap_core.c
+++ b/net/bluetooth/l2cap_core.c
@@ -4339,6 +4339,14 @@ static int l2cap_connect_create_rsp(struct l2cap_conn *conn,
 
 	l2cap_chan_lock(chan);
 
+	switch (chan->state) {
+	case BT_CLOSED:
+	case BT_DISCONN:
+		l2cap_chan_unlock(chan);
+		l2cap_chan_put(chan);
+		goto unlock;
+	}
+
 	switch (result) {
 	case L2CAP_CR_SUCCESS:
 		if (__l2cap_get_chan_by_dcid(conn, dcid)) {
@@ -4552,6 +4560,14 @@ static inline int l2cap_config_rsp(struct l2cap_conn *conn,
 	if (!chan)
 		return 0;
 
+	switch (chan->state) {
+	case BT_CLOSED:
+	case BT_CONNECT:
+	case BT_CONNECT2:
+	case BT_DISCONN:
+		goto done;
+	}
+
 	switch (result) {
 	case L2CAP_CONF_SUCCESS:
 		l2cap_conf_rfc_get(chan, rsp->data, len);
-- 
2.25.1