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From:   Niels Dossche <dossche.niels@gmail.com>
To:     linux-bluetooth@vger.kernel.org
Cc:     Marcel Holtmann <marcel@holtmann.org>,
        Johan Hedberg <johan.hedberg@gmail.com>,
        Luiz Augusto von Dentz <luiz.dentz@gmail.com>,
        Niels Dossche <dossche.niels@gmail.com>
Subject: [PATCH] Bluetooth: use hdev lock for accept_list and reject_list in conn req
Date:   Mon,  4 Apr 2022 02:34:04 +0200
Message-Id: <20220404003403.35690-1-dossche.niels@gmail.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

All accesses (both read and modifications) to
hdev->{accept,reject}_list are protected by hdev lock,
except the ones in hci_conn_request_evt. This can cause a race condition
in the form of a list corruption.
The solution is to protect these lists in hci_conn_request_evt as well.

I was unable to find the exact commit that introduced the issue for the
reject list, I was only able to find it for the accept list.

Note:
I am currently working on a static analyser to detect missing locks
using type-based static analysis as my master's thesis
in order to obtain my master's degree.
If you would like to have more details, please let me know.
This was a reported case. I manually verified the report by looking
at the code, so that I do not send wrong information or patches.
After concluding that this seems to be a true positive, I created
this patch. I have both compile-tested this patch and runtime-tested
this patch on x86_64. The effect on a running system could be a
potential race condition in exceptional cases.
This issue was found on Linux v5.17.1.

Fixes: a55bd29d5227 ("Bluetooth: Add white list lookup for incoming connection requests")
Signed-off-by: Niels Dossche <dossche.niels@gmail.com>
---
 net/bluetooth/hci_event.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/net/bluetooth/hci_event.c b/net/bluetooth/hci_event.c
index abaabfae19cc..b9038f24f46f 100644
--- a/net/bluetooth/hci_event.c
+++ b/net/bluetooth/hci_event.c
@@ -3222,8 +3222,11 @@ static void hci_conn_request_evt(struct hci_dev *hdev, void *data,
 		return;
 	}
 
+	hci_dev_lock(hdev);
+
 	if (hci_bdaddr_list_lookup(&hdev->reject_list, &ev->bdaddr,
 				   BDADDR_BREDR)) {
+		hci_dev_unlock(hdev);
 		hci_reject_conn(hdev, &ev->bdaddr);
 		return;
 	}
@@ -3236,14 +3239,13 @@ static void hci_conn_request_evt(struct hci_dev *hdev, void *data,
 	    !hci_dev_test_flag(hdev, HCI_CONNECTABLE) &&
 	    !hci_bdaddr_list_lookup_with_flags(&hdev->accept_list, &ev->bdaddr,
 					       BDADDR_BREDR)) {
+		hci_dev_unlock(hdev);
 		hci_reject_conn(hdev, &ev->bdaddr);
 		return;
 	}
 
 	/* Connection accepted */
 
-	hci_dev_lock(hdev);
-
 	ie = hci_inquiry_cache_lookup(hdev, &ev->bdaddr);
 	if (ie)
 		memcpy(ie->data.dev_class, ev->dev_class, 3);
-- 
2.35.1