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Message-Id: <20200128105322.1.If741898c727a5d948cbb10fdf9225b84efd443c8@changeid>
Date: Tue, 28 Jan 2020 10:54:14 -0800
From: Manish Mandlik <mmandlik@...gle.com>
To: Marcel Holtmann <marcel@...tmann.org>
Cc: Yoni Shavit <yshavit@...omium.org>,
linux-bluetooth@...r.kernel.org,
Alain Michaud <alainmichaud@...gle.com>,
Abhishek Pandit-Subedi <abhishekpandit@...omium.org>,
ChromeOS Bluetooth Upstreaming
<chromeos-bluetooth-upstreaming@...omium.org>,
Manish Mandlik <mmandlik@...gle.com>,
"David S. Miller" <davem@...emloft.net>,
Johan Hedberg <johan.hedberg@...il.com>,
netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
Jakub Kicinski <kuba@...nel.org>
Subject: [PATCH 1/1] 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 <mmandlik@...gle.com>
---
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 @@ static int l2cap_sock_recvmsg(struct socket *sock, struct msghdr *msg,
}
/* 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);
}
}
--
2.25.0.341.g760bfbb309-goog
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