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

Edward Adam Davis
2024-06-11T15:02:51Z

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 mutex in the rx callback of the sock to achieve synchronization between
the sock release and recv cb.

Reported-and-tested-by: syzbot+b7f6f8c9303466e16c8a@syzkaller.appspotmail.com
Signed-off-by: Edward Adam Davis <eadavis@qq.com>
---
net/bluetooth/l2cap_sock.c | 20 +++++++++++++++++---
1 file changed, 17 insertions(+), 3 deletions(-)

diff --git a/net/bluetooth/l2cap_sock.c b/net/bluetooth/l2cap_sock.c
index 6db60946c627..f3e9236293e1 100644
--- a/net/bluetooth/l2cap_sock.c
+++ b/net/bluetooth/l2cap_sock.c
@@ -1413,6 +1413,8 @@ static int l2cap_sock_release(struct socket *sock)
l2cap_chan_hold(chan);
l2cap_chan_lock(chan);

+ if (refcount_read(&sk->sk_refcnt) == 1)
+ chan->data = NULL;
sock_orphan(sk);
l2cap_sock_kill(sk);

@@ -1481,12 +1483,22 @@ 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;

- lock_sock(sk);
+ l2cap_chan_hold(chan);
+ l2cap_chan_lock(chan);
+ sk = chan->data;
+
+ if (!sk) {
+ l2cap_chan_unlock(chan);
+ l2cap_chan_put(chan);
+ return -ENXIO;
+ }

+ pi = l2cap_pi(sk);
+ lock_sock(sk);
if (chan->mode == L2CAP_MODE_ERTM && !list_empty(&pi->rx_busy)) {
err = -ENOMEM;
goto done;
@@ -1535,6 +1547,8 @@ static int l2cap_sock_recv_cb(struct l2cap_chan *chan, struct sk_buff *skb)

done:
release_sock(sk);
+ l2cap_chan_unlock(chan);
+ l2cap_chan_put(chan);

return err;
}
--
2.43.0