Re: [PATCH v2] Bluetooth: fix inconsistent lock state in sco

[Luiz Augusto von Dentz]

Hi Desmond,

On Tue, Jul 13, 2021 at 9:29 AM Desmond Cheong Zhi Xi
<desmondcheongzx@xxxxxxxxx> wrote:
>
> Syzbot reported an inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} lock
> usage in sco_conn_del and sco_sock_timeout that could lead to
> deadlocks.
>
> This inconsistent lock state can also happen in sco_conn_ready,
> rfcomm_connect_ind, and bt_accept_enqueue.
>
> The issue is that these functions take a spin lock on the socket with
> interrupts enabled, but sco_sock_timeout takes the lock in an IRQ
> context. This could lead to deadlocks:
>
>        CPU0
>        ----
>   lock(slock-AF_BLUETOOTH-BTPROTO_SCO);
>   <Interrupt>
>     lock(slock-AF_BLUETOOTH-BTPROTO_SCO);
>
>  *** DEADLOCK ***
>
> We fix this by ensuring that local bh is disabled before calling
> bh_lock_sock.
>
> After doing this, we additionally need to protect sco_conn_lock by
> disabling local bh.
>
> This is necessary because sco_conn_del makes a call to sco_chan_del
> while holding on to the sock lock, and sco_chan_del itself makes a
> call to sco_conn_lock. If sco_conn_lock is held elsewhere with
> interrupts enabled, there could still be a
> slock-AF_BLUETOOTH-BTPROTO_SCO --> &conn->lock#2 lock inversion as
> follows:
>
>         CPU0                    CPU1
>         ----                    ----
>    lock(&conn->lock#2);
>                                 local_irq_disable();
>                                 lock(slock-AF_BLUETOOTH-BTPROTO_SCO);
>                                 lock(&conn->lock#2);
>    <Interrupt>
>      lock(slock-AF_BLUETOOTH-BTPROTO_SCO);
>
>   *** DEADLOCK ***
>
> As sco_conn_del now disables local bh before calling sco_chan_del,
> instead of disabling local bh for the calls to sco_conn_lock in
> sco_chan_del, we instead wrap other calls to sco_chan_del with
> local_bh_disable/enable.
>
> Reported-by: syzbot+2f6d7c28bb4bf7e82060@xxxxxxxxxxxxxxxxxxxxxxxxx
> Tested-by: syzbot+2f6d7c28bb4bf7e82060@xxxxxxxxxxxxxxxxxxxxxxxxx
> Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@xxxxxxxxx>
> ---
>
> Hi,
>
> The previous version of this patch was a bit of a mess, so I made the
> following changes.
>
> v1 -> v2:
> - Instead of pulling out the clean-up code out from sco_chan_del and
> using it directly in sco_conn_del, disable local irqs for relevant
> sections.
> - Disable local irqs more thoroughly for instances of
> bh_lock_sock/bh_lock_sock_nested in the bluetooth subsystem.
> Specifically, the calls in af_bluetooth.c and rfcomm/sock.c are now made
> with local irqs disabled as well.
>
> Best wishes,
> Desmond
>
>  net/bluetooth/rfcomm/sock.c |  2 ++
>  net/bluetooth/sco.c         | 26 +++++++++++++++++++++++++-
>  2 files changed, 27 insertions(+), 1 deletion(-)
>
> diff --git a/net/bluetooth/rfcomm/sock.c b/net/bluetooth/rfcomm/sock.c
> index ae6f80730561..d8734abb2df4 100644
> --- a/net/bluetooth/rfcomm/sock.c
> +++ b/net/bluetooth/rfcomm/sock.c
> @@ -974,6 +974,7 @@ int rfcomm_connect_ind(struct rfcomm_session *s, u8 channel, struct rfcomm_dlc *
>         if (!parent)
>                 return 0;
>
> +       local_bh_disable();
>         bh_lock_sock(parent);
>
>         /* Check for backlog size */
> @@ -1002,6 +1003,7 @@ int rfcomm_connect_ind(struct rfcomm_session *s, u8 channel, struct rfcomm_dlc *
>
>  done:
>         bh_unlock_sock(parent);
> +       local_bh_enable();

Looks like you are touching RFCOMM as well, perhaps you should have it
split, also how about other sockets like L2CAP and HCI are they
affected? There seems to be a lot of problem with the likes of
bh_lock_sock I wonder if going with local_bh_disable is overall a
better way to handle.

>         if (test_bit(BT_SK_DEFER_SETUP, &bt_sk(parent)->flags))
>                 parent->sk_state_change(parent);
> diff --git a/net/bluetooth/sco.c b/net/bluetooth/sco.c
> index 3bd41563f118..2548b8f81473 100644
> --- a/net/bluetooth/sco.c
> +++ b/net/bluetooth/sco.c
> @@ -167,16 +167,22 @@ static void sco_conn_del(struct hci_conn *hcon, int err)
>         BT_DBG("hcon %p conn %p, err %d", hcon, conn, err);
>
>         /* Kill socket */
> +       local_bh_disable();
>         sco_conn_lock(conn);
>         sk = conn->sk;
>         sco_conn_unlock(conn);
> +       local_bh_enable();
>
>         if (sk) {
>                 sock_hold(sk);
> +
> +               local_bh_disable();
>                 bh_lock_sock(sk);
>                 sco_sock_clear_timer(sk);
>                 sco_chan_del(sk, err);
>                 bh_unlock_sock(sk);
> +               local_bh_enable();
> +
>                 sco_sock_kill(sk);
>                 sock_put(sk);
>         }
> @@ -202,6 +208,7 @@ static int sco_chan_add(struct sco_conn *conn, struct sock *sk,
>  {
>         int err = 0;
>
> +       local_bh_disable();
>         sco_conn_lock(conn);
>         if (conn->sk)
>                 err = -EBUSY;
> @@ -209,6 +216,7 @@ static int sco_chan_add(struct sco_conn *conn, struct sock *sk,
>                 __sco_chan_add(conn, sk, parent);
>
>         sco_conn_unlock(conn);
> +       local_bh_enable();
>         return err;
>  }
>
> @@ -303,9 +311,11 @@ static void sco_recv_frame(struct sco_conn *conn, struct sk_buff *skb)
>  {
>         struct sock *sk;
>
> +       local_bh_disable();
>         sco_conn_lock(conn);
>         sk = conn->sk;
>         sco_conn_unlock(conn);
> +       local_bh_enable();
>
>         if (!sk)
>                 goto drop;
> @@ -420,18 +430,25 @@ static void __sco_sock_close(struct sock *sk)
>                 if (sco_pi(sk)->conn->hcon) {
>                         sk->sk_state = BT_DISCONN;
>                         sco_sock_set_timer(sk, SCO_DISCONN_TIMEOUT);
> +                       local_bh_disable();
>                         sco_conn_lock(sco_pi(sk)->conn);
>                         hci_conn_drop(sco_pi(sk)->conn->hcon);
>                         sco_pi(sk)->conn->hcon = NULL;
>                         sco_conn_unlock(sco_pi(sk)->conn);
> -               } else
> +                       local_bh_enable();
> +               } else {
> +                       local_bh_disable();
>                         sco_chan_del(sk, ECONNRESET);
> +                       local_bh_enable();
> +               }
>                 break;
>
>         case BT_CONNECT2:
>         case BT_CONNECT:
>         case BT_DISCONN:
> +               local_bh_disable();
>                 sco_chan_del(sk, ECONNRESET);
> +               local_bh_enable();
>                 break;
>
>         default:
> @@ -1084,21 +1101,26 @@ static void sco_conn_ready(struct sco_conn *conn)
>
>         if (sk) {
>                 sco_sock_clear_timer(sk);
> +               local_bh_disable();
>                 bh_lock_sock(sk);
>                 sk->sk_state = BT_CONNECTED;
>                 sk->sk_state_change(sk);
>                 bh_unlock_sock(sk);
> +               local_bh_enable();
>         } else {
> +               local_bh_disable();
>                 sco_conn_lock(conn);
>
>                 if (!conn->hcon) {
>                         sco_conn_unlock(conn);
> +                       local_bh_enable();
>                         return;
>                 }
>
>                 parent = sco_get_sock_listen(&conn->hcon->src);
>                 if (!parent) {
>                         sco_conn_unlock(conn);
> +                       local_bh_enable();
>                         return;
>                 }
>
> @@ -1109,6 +1131,7 @@ static void sco_conn_ready(struct sco_conn *conn)
>                 if (!sk) {
>                         bh_unlock_sock(parent);
>                         sco_conn_unlock(conn);
> +                       local_bh_enable();
>                         return;
>                 }
>
> @@ -1131,6 +1154,7 @@ static void sco_conn_ready(struct sco_conn *conn)
>                 bh_unlock_sock(parent);
>
>                 sco_conn_unlock(conn);
> +               local_bh_enable();
>         }
>  }
>
> --
> 2.25.1
>


-- 
Luiz Augusto von Dentz