[PATCH 06/11] Bluetooth: ISO: hold sk properly in iso_conn_ready

[Pauli Virtanen]

sk deref in iso_conn_ready must be done either under conn->lock, or
holding a refcount, to avoid concurrent close. conn->sk is currently
accessed without either:

    [Task 1]            [Task 2]
                        iso_sock_release
    iso_conn_ready
      sk = conn->sk
                          lock_sock(sk)
                            conn->sk = NULL
      lock_sock(sk)
                          release_sock(sk)
                          iso_sock_kill(sk)
       UAF on sk deref

Fix possible UAF by holding sk refcount in iso_conn_ready().  Also
recheck after lock_sock that the socket is still valid.  Adjust locking
so conn->sk is cleared only under lock_sock.

Fixes: 27c24fda62b60 ("Bluetooth: switch to lock_sock in SCO")
Signed-off-by: Pauli Virtanen <pav@xxxxxx>
---
 net/bluetooth/iso.c | 34 +++++++++++++++++++++++-----------
 1 file changed, 23 insertions(+), 11 deletions(-)

diff --git a/net/bluetooth/iso.c b/net/bluetooth/iso.c
index 5de4a2f886eb..80a58275891d 100644
--- a/net/bluetooth/iso.c
+++ b/net/bluetooth/iso.c
@@ -805,11 +805,13 @@ static void iso_sock_kill(struct sock *sk)
 	BT_DBG("sk %p state %d", sk, sk->sk_state);
 
 	/* Sock is dead, so set conn->sk to NULL to avoid possible UAF */
+	lock_sock(sk);
 	if (iso_pi(sk)->conn) {
 		iso_conn_lock(iso_pi(sk)->conn);
 		iso_pi(sk)->conn->sk = NULL;
 		iso_conn_unlock(iso_pi(sk)->conn);
 	}
+	release_sock(sk);
 
 	/* Kill poor orphan */
 	bt_sock_unlink(&iso_sk_list, sk);
@@ -2047,23 +2049,17 @@ static void iso_sock_ready(struct sock *sk)
 {
 	BT_DBG("sk %p", sk);
 
-	if (!sk)
-		return;
-
-	lock_sock(sk);
+	lockdep_assert(lockdep_sock_is_held(sk));
 
 	switch (sk->sk_state) {
 	case BT_DISCONN:
 	case BT_CLOSED:
-		release_sock(sk);
 		return;
 	}
 
 	iso_sock_clear_timer(sk);
 	sk->sk_state = BT_CONNECTED;
 	sk->sk_state_change(sk);
-
-	release_sock(sk);
 }
 
 static bool iso_match_big(struct sock *sk, void *data)
@@ -2093,7 +2089,7 @@ static bool iso_match_dst(struct sock *sk, void *data)
 static void iso_conn_ready(struct iso_conn *conn)
 {
 	struct sock *parent = NULL;
-	struct sock *sk = conn->sk;
+	struct sock *sk;
 	struct hci_ev_le_big_sync_established *ev = NULL;
 	struct hci_ev_le_pa_sync_established *ev2 = NULL;
 	struct hci_ev_le_per_adv_report *ev3 = NULL;
@@ -2102,7 +2098,22 @@ static void iso_conn_ready(struct iso_conn *conn)
 
 	BT_DBG("conn %p", conn);
 
+	iso_conn_lock(conn);
+	sk = iso_sock_hold(conn);
+	iso_conn_unlock(conn);
+
 	if (sk) {
+		lock_sock(sk);
+
+		/* conn->sk may have become NULL if racing with sk close, but
+		 * due to held hdev->lock, it can't become different sk.
+		 */
+		if (!conn->sk) {
+			release_sock(sk);
+			sock_put(sk);
+			return;
+		}
+
 		/* Attempt to update source address in case of BIS Sender if
 		 * the advertisement is using a random address.
 		 */
@@ -2115,14 +2126,15 @@ static void iso_conn_ready(struct iso_conn *conn)
 			adv = hci_find_adv_instance(bis->hdev,
 						    bis->iso_qos.bcast.bis);
 			if (adv && bacmp(&adv->random_addr, BDADDR_ANY)) {
-				lock_sock(sk);
 				iso_pi(sk)->src_type = BDADDR_LE_RANDOM;
 				bacpy(&iso_pi(sk)->src, &adv->random_addr);
-				release_sock(sk);
 			}
 		}
 
-		iso_sock_ready(conn->sk);
+		iso_sock_ready(sk);
+
+		release_sock(sk);
+		sock_put(sk);
 	} else {
 		hcon = conn->hcon;
 		if (!hcon)
-- 
2.55.0