[PATCH V3] Bluetooth/l2cap: sync sock recv cb and release

Edward Adam Davis
2024-06-25T10:20:27Z

The problem occurs between the system call to close the sock and hci_rx_work,
where the former releases the sock and the latter accesses it without lock protection.

CPU0 CPU1
---- ----
sock_close hci_rx_work
l2cap_sock_release hci_acldata_packet
l2cap_sock_kill l2cap_recv_frame
sk_free l2cap_conless_channel
l2cap_sock_recv_cb

If hci_rx_work processes the data that needs to be received before the sock is
closed, then everything is normal; Otherwise, the work thread may access the
released sock when receiving data.

Add a chan lock in the l2cap_conless_channel of the sock to achieve sync
between the sock release and recv cb.

Sock is dead, so set chan data to NULL, avoid others use invalid sock pointer.

Reported-by: syzbot+b7f6f8c9303466e16c8a@syzkaller.appspotmail.com
Signed-off-by: Edward Adam Davis <eadavis@qq.com>
---
net/bluetooth/l2cap_core.c | 3 +++
net/bluetooth/l2cap_sock.c | 13 +++++++++++--
2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
index aed025734d04..35a9534eb62d 100644
--- a/net/bluetooth/l2cap_core.c
+++ b/net/bluetooth/l2cap_core.c
@@ -6771,10 +6771,13 @@ static void l2cap_conless_channel(struct l2cap_conn *conn, __le16 psm,
bacpy(&bt_cb(skb)->l2cap.bdaddr, &hcon->dst);
bt_cb(skb)->l2cap.psm = psm;

+ l2cap_chan_lock(chan);
if (!chan->ops->recv(chan, skb)) {
+ l2cap_chan_unlock(chan);
l2cap_chan_put(chan);
return;
}
+ l2cap_chan_unlock(chan);

drop:
l2cap_chan_put(chan);
diff --git a/net/bluetooth/l2cap_sock.c b/net/bluetooth/l2cap_sock.c
index 6db60946c627..25091fb992a7 100644
--- a/net/bluetooth/l2cap_sock.c
+++ b/net/bluetooth/l2cap_sock.c
@@ -1239,6 +1239,10 @@ static void l2cap_sock_kill(struct sock *sk)

BT_DBG("sk %p state %s", sk, state_to_string(sk->sk_state));

+ /* Sock is dead, so set chan data to NULL, avoid other task use invalid
+ * sock pointer.
+ */
+ l2cap_pi(sk)->chan->data = NULL;
/* Kill poor orphan */

l2cap_chan_put(l2cap_pi(sk)->chan);
@@ -1481,11 +1485,16 @@ static struct l2cap_chan *l2cap_sock_new_connection_cb(struct l2cap_chan *chan)

static int l2cap_sock_recv_cb(struct l2cap_chan *chan, struct sk_buff *skb)
{
- struct sock *sk = chan->data;
- struct l2cap_pinfo *pi = l2cap_pi(sk);
+ struct sock *sk;
+ struct l2cap_pinfo *pi;
int err;

+ if (!chan->data)
+ return -ENXIO;
+
+ sk = chan->data;
lock_sock(sk);
+ pi = l2cap_pi(sk);

if (chan->mode == L2CAP_MODE_ERTM && !list_empty(&pi->rx_busy)) {
err = -ENOMEM;
--
2.43.0