From: Manish Mandlik mmandlik@google.com
[ Upstream commit 6c08fc896b60893c5d673764b0668015d76df462 ]
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 mmandlik@google.com Signed-off-by: Marcel Holtmann marcel@holtmann.org Signed-off-by: Sasha Levin sashal@kernel.org --- 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 0e31bbe1256cd..f6112f495a36c 100644 --- a/net/bluetooth/l2cap_core.c +++ b/net/bluetooth/l2cap_core.c @@ -403,6 +403,9 @@ 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) @@ -415,12 +418,12 @@ 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) @@ -1714,9 +1717,9 @@ 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); }
@@ -4316,6 +4319,7 @@ 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); @@ -4324,12 +4328,11 @@ 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); @@ -4361,20 +4364,21 @@ 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 d9bbbded49ef8..cb024c25530a3 100644 --- a/net/bluetooth/l2cap_sock.c +++ b/net/bluetooth/l2cap_sock.c @@ -1038,7 +1038,7 @@ 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) { @@ -1199,8 +1199,15 @@ 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; }
@@ -1218,12 +1225,15 @@ 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); } }