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From:   Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
To:     marcel@holtmann.org, johan.hedberg@gmail.com, luiz.dentz@gmail.com,
        davem@davemloft.net, kuba@kernel.org
Cc:     Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>,
        linux-bluetooth@vger.kernel.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, skhan@linuxfoundation.org,
        gregkh@linuxfoundation.org,
        linux-kernel-mentees@lists.linuxfoundation.org,
        syzbot+66264bf2fd0476be7e6c@syzkaller.appspotmail.com
Subject: [PATCH] Bluetooth: skip invalid hci_sync_conn_complete_evt
Date:   Wed, 21 Jul 2021 18:17:10 +0800
Message-Id: <20210721101710.82974-1-desmondcheongzx@gmail.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
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Syzbot reported a corrupted list in kobject_add_internal [1]. This
happens when multiple HCI_EV_SYNC_CONN_COMPLETE event packets with
status 0 are sent for the same HCI connection. This causes us to
register the device more than once which corrupts the kset list.

To fix this, in hci_sync_conn_complete_evt, we check whether we're
trying to process the same HCI_EV_SYNC_CONN_COMPLETE event multiple
times for one connection. If that's the case, the event is invalid, so
we skip further processing and exit.

Link: https://syzkaller.appspot.com/bug?extid=66264bf2fd0476be7e6c [1]
Reported-by: syzbot+66264bf2fd0476be7e6c@syzkaller.appspotmail.com
Tested-by: syzbot+66264bf2fd0476be7e6c@syzkaller.appspotmail.com
Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
---
 net/bluetooth/hci_event.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/bluetooth/hci_event.c b/net/bluetooth/hci_event.c
index 016b2999f219..091a92338492 100644
--- a/net/bluetooth/hci_event.c
+++ b/net/bluetooth/hci_event.c
@@ -4373,6 +4373,8 @@ static void hci_sync_conn_complete_evt(struct hci_dev *hdev,
 
 	switch (ev->status) {
 	case 0x00:
+		if (conn->state == BT_CONNECTED)
+			goto unlock;  /* Already connected, event not valid */
 		conn->handle = __le16_to_cpu(ev->handle);
 		conn->state  = BT_CONNECTED;
 		conn->type   = ev->link_type;
-- 
2.25.1