From 6c08fc896b60893c5d673764b0668015d76df462 Mon Sep 17 00:00:00 2001 From: Manish Mandlik Date: Tue, 28 Jan 2020 10:54:14 -0800 Subject: [PATCH] Bluetooth: Fix refcount use-after-free issue There is no lock preventing both l2cap_sock_release() and chan->ops->close() from running at the same time. If we consider Thread A running l2cap_chan_timeout() and Thread B running l2cap_sock_release(), expected behavior is: A::l2cap_chan_timeout()->l2cap_chan_close()->l2cap_sock_teardown_cb() A::l2cap_chan_timeout()->l2cap_sock_close_cb()->l2cap_sock_kill() B::l2cap_sock_release()->sock_orphan() B::l2cap_sock_release()->l2cap_sock_kill() where, sock_orphan() clears "sk->sk_socket" and l2cap_sock_teardown_cb() marks socket as SOCK_ZAPPED. In l2cap_sock_kill(), there is an "if-statement" that checks if both sock_orphan() and sock_teardown() has been run i.e. sk->sk_socket is NULL and socket is marked as SOCK_ZAPPED. Socket is killed if the condition is satisfied. In the race condition, following occurs: A::l2cap_chan_timeout()->l2cap_chan_close()->l2cap_sock_teardown_cb() B::l2cap_sock_release()->sock_orphan() B::l2cap_sock_release()->l2cap_sock_kill() A::l2cap_chan_timeout()->l2cap_sock_close_cb()->l2cap_sock_kill() In this scenario, "if-statement" is true in both B::l2cap_sock_kill() and A::l2cap_sock_kill() and we hit "refcount: underflow; use-after-free" bug. Similar condition occurs at other places where teardown/sock_kill is happening: l2cap_disconnect_rsp()->l2cap_chan_del()->l2cap_sock_teardown_cb() l2cap_disconnect_rsp()->l2cap_sock_close_cb()->l2cap_sock_kill() l2cap_conn_del()->l2cap_chan_del()->l2cap_sock_teardown_cb() l2cap_conn_del()->l2cap_sock_close_cb()->l2cap_sock_kill() l2cap_disconnect_req()->l2cap_chan_del()->l2cap_sock_teardown_cb() l2cap_disconnect_req()->l2cap_sock_close_cb()->l2cap_sock_kill() l2cap_sock_cleanup_listen()->l2cap_chan_close()->l2cap_sock_teardown_cb() l2cap_sock_cleanup_listen()->l2cap_sock_kill() Protect teardown/sock_kill and orphan/sock_kill by adding hold_lock on l2cap channel to ensure that the socket is killed only after marked as zapped and orphan. Signed-off-by: Manish Mandlik Signed-off-by: Marcel Holtmann --- net/bluetooth/l2cap_core.c | 26 +++++++++++++++----------- net/bluetooth/l2cap_sock.c | 16 +++++++++++++--- 2 files changed, 28 insertions(+), 14 deletions(-) diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c index 195459a1e53e..dd2021270b8a 100644 --- a/net/bluetooth/l2cap_core.c +++ b/net/bluetooth/l2cap_core.c @@ -419,6 +419,9 @@ static void l2cap_chan_timeout(struct work_struct *work) BT_DBG("chan %p state %s", chan, state_to_string(chan->state)); mutex_lock(&conn->chan_lock); + /* __set_chan_timer() calls l2cap_chan_hold(chan) while scheduling + * this work. No need to call l2cap_chan_hold(chan) here again. + */ l2cap_chan_lock(chan); if (chan->state == BT_CONNECTED || chan->state == BT_CONFIG) @@ -431,12 +434,12 @@ static void l2cap_chan_timeout(struct work_struct *work) l2cap_chan_close(chan, reason); - l2cap_chan_unlock(chan); - chan->ops->close(chan); - mutex_unlock(&conn->chan_lock); + l2cap_chan_unlock(chan); l2cap_chan_put(chan); + + mutex_unlock(&conn->chan_lock); } struct l2cap_chan *l2cap_chan_create(void) @@ -1737,9 +1740,9 @@ static void l2cap_conn_del(struct hci_conn *hcon, int err) l2cap_chan_del(chan, err); - l2cap_chan_unlock(chan); - chan->ops->close(chan); + + l2cap_chan_unlock(chan); l2cap_chan_put(chan); } @@ -4405,6 +4408,7 @@ static inline int l2cap_disconnect_req(struct l2cap_conn *conn, return 0; } + l2cap_chan_hold(chan); l2cap_chan_lock(chan); rsp.dcid = cpu_to_le16(chan->scid); @@ -4413,12 +4417,11 @@ static inline int l2cap_disconnect_req(struct l2cap_conn *conn, chan->ops->set_shutdown(chan); - l2cap_chan_hold(chan); l2cap_chan_del(chan, ECONNRESET); - l2cap_chan_unlock(chan); - chan->ops->close(chan); + + l2cap_chan_unlock(chan); l2cap_chan_put(chan); mutex_unlock(&conn->chan_lock); @@ -4450,20 +4453,21 @@ static inline int l2cap_disconnect_rsp(struct l2cap_conn *conn, return 0; } + l2cap_chan_hold(chan); l2cap_chan_lock(chan); if (chan->state != BT_DISCONN) { l2cap_chan_unlock(chan); + l2cap_chan_put(chan); mutex_unlock(&conn->chan_lock); return 0; } - l2cap_chan_hold(chan); l2cap_chan_del(chan, 0); - l2cap_chan_unlock(chan); - chan->ops->close(chan); + + l2cap_chan_unlock(chan); l2cap_chan_put(chan); mutex_unlock(&conn->chan_lock); diff --git a/net/bluetooth/l2cap_sock.c b/net/bluetooth/l2cap_sock.c index a7be8b59b3c2..ab65304f3f63 100644 --- a/net/bluetooth/l2cap_sock.c +++ b/net/bluetooth/l2cap_sock.c @@ -1042,7 +1042,7 @@ done: } /* Kill socket (only if zapped and orphan) - * Must be called on unlocked socket. + * Must be called on unlocked socket, with l2cap channel lock. */ static void l2cap_sock_kill(struct sock *sk) { @@ -1203,8 +1203,15 @@ static int l2cap_sock_release(struct socket *sock) err = l2cap_sock_shutdown(sock, 2); + l2cap_chan_hold(l2cap_pi(sk)->chan); + l2cap_chan_lock(l2cap_pi(sk)->chan); + sock_orphan(sk); l2cap_sock_kill(sk); + + l2cap_chan_unlock(l2cap_pi(sk)->chan); + l2cap_chan_put(l2cap_pi(sk)->chan); + return err; } @@ -1222,12 +1229,15 @@ static void l2cap_sock_cleanup_listen(struct sock *parent) BT_DBG("child chan %p state %s", chan, state_to_string(chan->state)); + l2cap_chan_hold(chan); l2cap_chan_lock(chan); + __clear_chan_timer(chan); l2cap_chan_close(chan, ECONNRESET); - l2cap_chan_unlock(chan); - l2cap_sock_kill(sk); + + l2cap_chan_unlock(chan); + l2cap_chan_put(chan); } }