sco_recv_scodata() upgrades the weak hcon->sco_data back-pointer to a strong reference under hdev->lock: hci_dev_lock(hdev); hcon = hci_conn_hash_lookup_handle(hdev, handle); ... conn = sco_conn_hold_unless_zero(hcon->sco_data); hci_dev_unlock(hdev); but the pointer is cleared from the other side without that lock. When the last sco_conn reference is dropped, sco_conn_free() ran conn->hcon->sco_data = NULL; with no hdev->lock held, so the RX path could read hcon->sco_data and call kref_get_unless_zero() on an sco_conn that was concurrently freed: BUG: KASAN: slab-use-after-free in sco_conn_hold_unless_zero+0xbe/0x160 Write of size 4 by task kworker/u17:0 Workqueue: hci0 hci_rx_work Call Trace: sco_conn_hold_unless_zero+0xbe/0x160 sco_recv_scodata+0x13f/0x490 hci_rx_work+0x3af/0x730 kref_get_unless_zero() only guards against a zero refcount, not against the backing memory already being freed. Give hcon->sco_data an actual reference on the sco_conn it points to, so the object cannot be freed while the pointer is still installed, and only clear and drop it from sco_conn_del(), which runs under hdev->lock (its callers, sco_connect_cfm() and sco_disconn_cfm(), hold it). The reader in sco_recv_scodata() also takes hdev->lock, so the store and the read are now serialised: the RX path either observes NULL or a reference that is guaranteed to stay valid until it drops its own. sco_conn_add() no longer hands its kref_init() reference to the caller as the connection's only reference; that initial reference is the one owned by hcon->sco_data, and callers get their own via sco_conn_hold(). Because the sco_conn can now outlive the socket (the association keeps it alive until the link goes down), the hci_conn can no longer be dropped from sco_conn_free() without regressing socket close: closing a connected SCO socket must still tear the link down. Move hci_conn ownership to the socket instead: __sco_chan_add() takes an hci_conn reference and it is released from sco_chan_del() and sco_sock_destruct(), exactly once. The sco_conn no longer owns an hci_conn reference, so sco_conn_add() stops consuming one and sco_connect() drops the hci_connect_sco() reference on every path; sco_connect_cfm() no longer needs its hci_conn_hold() dance. Fixes: e6720779ae61 ("Bluetooth: SCO: Use kref to track lifetime of sco_conn") Cc: stable@vger.kernel.org Suggested-by: Pauli Virtanen Signed-off-by: Aldo Ariel Panzardo --- v3: fix two UAFs found by Pauli Virtanen in the v2 review: - sco_chan_del(): drop hci_conn ref before clearing conn->sk so that sco_conn_del() on another CPU cannot free hci_conn under our feet - sco_sock_destruct(): same ordering fix - remove dead branch in sco_conn_add() (conn->hcon == NULL impossible) - move hci_conn_drop in sco_connect() tighter after __sco_chan_add() v2: quote inlined code and KASAN splat with spaces (bluez CI gitlint); no functional change. diff --git a/net/bluetooth/sco.c b/net/bluetooth/sco.c index 3d4362a..a2f17ab 100644 --- a/net/bluetooth/sco.c +++ b/net/bluetooth/sco.c @@ -84,12 +84,14 @@ static void sco_conn_free(struct kref *ref) if (conn->sk) sco_pi(conn->sk)->conn = NULL; - if (conn->hcon) { - conn->hcon->sco_data = NULL; - hci_conn_drop(conn->hcon); - } + /* hcon->sco_data is cleared and the association's reference on the + * sco_conn is dropped in sco_conn_del() under hdev->lock, and the + * hci_conn is now owned by the socket (held in __sco_chan_add() and + * dropped in sco_chan_del()/sco_sock_destruct()), so there is nothing + * left to release towards hcon here. + */ - /* Ensure no more work items will run since hci_conn has been dropped */ + /* Ensure no more work items will run before the connection is freed */ disable_delayed_work_sync(&conn->timeout_work); kfree(conn); @@ -188,25 +190,19 @@ static void sco_sock_clear_timer(struct sock *sk) } /* ---- SCO connections ---- */ -/* Consumes a reference on @hcon, which the returned sco_conn owns until it is - * freed. On failure (NULL return) the reference is left for the caller to drop. +/* Returns a new reference the caller must drop with sco_conn_put(). The + * hcon->sco_data association holds its own reference on the sco_conn for the + * connection's lifetime; it is dropped in sco_conn_del() under hdev->lock. + * @hcon is not consumed: the hci_conn reference is taken and owned by the + * socket in __sco_chan_add(). */ static struct sco_conn *sco_conn_add(struct hci_conn *hcon) { struct sco_conn *conn = hcon->sco_data; conn = sco_conn_hold_unless_zero(conn); - if (conn) { - if (!conn->hcon) { - sco_conn_lock(conn); - conn->hcon = hcon; - sco_conn_unlock(conn); - } else { - /* conn already owns a reference on hcon */ - hci_conn_drop(hcon); - } + if (conn) return conn; - } conn = kzalloc_obj(struct sco_conn); if (!conn) @@ -227,7 +223,10 @@ static struct sco_conn *sco_conn_add(struct hci_conn *hcon) BT_DBG("hcon %p conn %p", hcon, conn); - return conn; + /* kref_init() above set the association reference owned by + * hcon->sco_data; hand the caller its own reference. + */ + return sco_conn_hold(conn); } /* Delete channel. @@ -242,6 +241,19 @@ static void sco_chan_del(struct sock *sk, int err) BT_DBG("sk %p, conn %p, err %d", sk, conn, err); if (conn) { + struct hci_conn *hcon; + + sco_conn_lock(conn); + hcon = conn->hcon; + sco_conn_unlock(conn); + + /* Drop the socket's hci_conn reference BEFORE clearing + * conn->sk, so sco_conn_del() on another CPU cannot free + * the hci_conn while we still hold a pointer to it. + */ + if (hcon) + hci_conn_drop(hcon); + sco_conn_lock(conn); conn->sk = NULL; sco_conn_unlock(conn); @@ -266,6 +278,13 @@ static void sco_conn_del(struct hci_conn *hcon, int err) BT_DBG("hcon %p conn %p, err %d", hcon, conn, err); + /* Detach from the hci_conn and drop the association's reference. + * The caller holds hdev->lock, which serialises this against the + * read of hcon->sco_data in sco_recv_scodata(). + */ + hcon->sco_data = NULL; + sco_conn_put(conn); + sco_conn_lock(conn); sk = sco_sock_hold(conn); sco_conn_unlock(conn); @@ -290,6 +309,11 @@ static void __sco_chan_add(struct sco_conn *conn, struct sock *sk, sco_pi(sk)->conn = sco_conn_hold(conn); conn->sk = sk; + /* The socket owns an hci_conn reference for as long as it stays + * attached; it is dropped in sco_chan_del()/sco_sock_destruct(). + */ + hci_conn_hold(conn->hcon); + if (parent) bt_accept_enqueue(parent, sk, true); } @@ -371,6 +395,7 @@ static int sco_connect(struct sock *sk) if (sk->sk_state != BT_OPEN && sk->sk_state != BT_BOUND) { release_sock(sk); sco_conn_put(conn); + hci_conn_drop(hcon); err = -EBADFD; goto unlock; } @@ -379,9 +404,13 @@ static int sco_connect(struct sock *sk) sco_conn_put(conn); if (err) { release_sock(sk); + hci_conn_drop(hcon); goto unlock; } + /* __sco_chan_add() took its own hci_conn reference; drop ours. */ + hci_conn_drop(hcon); + /* Update source addr of the socket */ bacpy(&sco_pi(sk)->src, &hcon->src); @@ -495,9 +524,26 @@ static struct sock *sco_get_sock_listen(bdaddr_t *src) static void sco_sock_destruct(struct sock *sk) { + struct sco_conn *conn = sco_pi(sk)->conn; + BT_DBG("sk %p", sk); - sco_conn_put(sco_pi(sk)->conn); + /* If the channel was not already torn down via sco_chan_del(), drop + * the socket's own references here. + */ + if (conn) { + struct hci_conn *hcon; + + sco_conn_lock(conn); + hcon = conn->hcon; + sco_conn_unlock(conn); + + if (hcon) + hci_conn_drop(hcon); + sco_pi(sk)->conn = NULL; + sco_conn_put(conn); + return; + } skb_queue_purge(&sk->sk_receive_queue); skb_queue_purge(&sk->sk_write_queue); @@ -1511,12 +1557,10 @@ static void sco_connect_cfm(struct hci_conn *hcon, __u8 status) if (!status) { struct sco_conn *conn; - conn = sco_conn_add(hci_conn_hold(hcon)); + conn = sco_conn_add(hcon); if (conn) { sco_conn_ready(conn); sco_conn_put(conn); - } else { - hci_conn_drop(hcon); } } else sco_conn_del(hcon, bt_to_errno(status)); -- 2.43.0