Received-SPF: pass (google.com: domain of linux-bluetooth-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
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 v2] Bluetooth: protect remote oob data in build_pairing_cmd's callsites
Date:   Tue, 13 Sep 2022 19:39:08 +0200
Message-Id: <20220913173907.13792-1-dossche.niels@gmail.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

Accesses to hci_dev->remote_oob_data are protected by the hdev lock,
except for the access in build_pairing_cmd via hci_find_remote_oob_data.
Adding the lock around the access in build_pairing_cmd would cause a
lock ordering problem: the l2cap_chan_lock is taken in the caller
smp_conn_security, while the hdev lock should be taken before the chan
lock.
The solution is to add the hdev lock to the callsites of
build_pairing_cmd.

Fixes: 02b05bd8b0a6 ("Bluetooth: Set SMP OOB flag if OOB data is available")
Signed-off-by: Niels Dossche <dossche.niels@gmail.com>
---

Note:
I am currently working on a static analyser to detect missing locks
using type-based static analysis, which reported the missing lock on
v6.0-rc5. 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 only managed to compile-test this patch on x86_64.
After applying the patch, my analyser no longer reports the potential
bug.

 net/bluetooth/smp.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/net/bluetooth/smp.c b/net/bluetooth/smp.c
index 11f853d0500f..6611a789b6c1 100644
--- a/net/bluetooth/smp.c
+++ b/net/bluetooth/smp.c
@@ -1803,7 +1803,9 @@ static u8 smp_cmd_pairing_req(struct l2cap_conn *conn, struct sk_buff *skb)
 		return 0;
 	}
 
+	hci_dev_lock(hdev);
 	build_pairing_cmd(conn, req, &rsp, auth);
+	hci_dev_unlock(hdev);
 
 	if (rsp.auth_req & SMP_AUTH_SC) {
 		set_bit(SMP_FLAG_SC, &smp->flags);
@@ -2335,7 +2337,9 @@ static u8 smp_cmd_security_req(struct l2cap_conn *conn, struct sk_buff *skb)
 	skb_pull(skb, sizeof(*rp));
 
 	memset(&cp, 0, sizeof(cp));
+	hci_dev_lock(hdev);
 	build_pairing_cmd(conn, &cp, NULL, auth);
+	hci_dev_unlock(hdev);
 
 	smp->preq[0] = SMP_CMD_PAIRING_REQ;
 	memcpy(&smp->preq[1], &cp, sizeof(cp));
@@ -2380,6 +2384,7 @@ int smp_conn_security(struct hci_conn *hcon, __u8 sec_level)
 		return 1;
 	}
 
+	hci_dev_lock(hcon->hdev);
 	l2cap_chan_lock(chan);
 
 	/* If SMP is already in progress ignore this request */
@@ -2435,6 +2440,7 @@ int smp_conn_security(struct hci_conn *hcon, __u8 sec_level)
 
 unlock:
 	l2cap_chan_unlock(chan);
+	hci_dev_unlock(hcon->hdev);
 	return ret;
 }
 
-- 
2.37.3