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

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@syzkaller.appspotmail.com
Tested-by: syzbot+2f6d7c28bb4bf7e82060@syzkaller.appspotmail.com
Signed-off-by: Desmond Cheong Zhi Xi <redacted>
---

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();

        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