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From:   Soenke Huster <soenke.huster@eknoes.de>
To:     Marcel Holtmann <marcel@holtmann.org>,
        Johan Hedberg <johan.hedberg@gmail.com>,
        Luiz Augusto von Dentz <luiz.dentz@gmail.com>,
        "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>
Cc:     Soenke Huster <soenke.huster@eknoes.de>,
        linux-bluetooth@vger.kernel.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: [PATCH v3] Bluetooth: fix null ptr deref on hci_sync_conn_complete_evt
Date:   Fri, 14 Jan 2022 17:44:02 +0100
Message-Id: <20220114164401.330248-1-soenke.huster@eknoes.de>
MIME-Version: 1.0
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This event is just specified for SCO and eSCO link types.
On the reception of a HCI_Synchronous_Connection_Complete for a BDADDR
of an existing LE connection, LE link type and a status that triggers the
second case of the packet processing a NULL pointer dereference happens,
as conn->link is NULL.

Signed-off-by: Soenke Huster <soenke.huster@eknoes.de>
---
v3: Replace if with switch, reference spec

I found this null pointer dereference while fuzzing bluetooth-next.
On the described behaviour, a null ptr deref in line 4723 happens, as
conn->link is NULL. According to the Core spec, Link_Type must be SCO or eSCO,
all other values are reserved for future use. Checking that mitigates a null
pointer dereference.

 net/bluetooth/hci_event.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/net/bluetooth/hci_event.c b/net/bluetooth/hci_event.c
index fc30f4c03d29..e47cde778b1c 100644
--- a/net/bluetooth/hci_event.c
+++ b/net/bluetooth/hci_event.c
@@ -4661,6 +4661,19 @@ static void hci_sync_conn_complete_evt(struct hci_dev *hdev, void *data,
 	struct hci_ev_sync_conn_complete *ev = data;
 	struct hci_conn *conn;
 
+	switch (ev->link_type) {
+	case SCO_LINK:
+	case ESCO_LINK:
+		break;
+	default:
+		/* As per Core 5.3 Vol 4 Part E 7.7.35 (p.2219), Link_Type
+		 * for HCI_Synchronous_Connection_Complete is limited to
+		 * either SCO or eSCO
+		 */
+		bt_dev_err(hdev, "Ignoring connect complete event for invalid link type");
+		return;
+	}
+
 	bt_dev_dbg(hdev, "status 0x%2.2x", ev->status);
 
 	hci_dev_lock(hdev);
-- 
2.34.1