Messages in this thread | | | Subject | Re: [PATCH v3 1/2] Bluetooth: fix inconsistent lock state in SCO | From | Desmond Cheong Zhi Xi <> | Date | Tue, 27 Jul 2021 13:13:27 +0800 |
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On 27/7/21 8:30 am, Luiz Augusto von Dentz wrote: > Hi Desmond, > > On Wed, Jul 21, 2021 at 2:39 AM Desmond Cheong Zhi Xi > <desmondcheongzx@gmail.com> 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); > > Having a second look at this, it does seem this is due to use of > sk->sk_timer which apparently run its callback on IRQ context, so I > wonder if wouldn't be a better idea to switch to a delayed_work to > avoid having to deal with the likes of local_bh_disable, in fact it > seems we have been misusing it since the documentation says it is for > sock cleanup not for handling things like SNDTIMEO, we don't really > use it for other socket types so I wonder when we start using > delayed_work we forgot about sco.c. >
Hi Luiz,
That makes sense to me. I don't think there's a need for the timeout to be run in an IRQ context.
I'll prepare a patch for this, thanks for the suggestion.
>> *** 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 *** >> >> Although sco_conn_del disables local bh before calling sco_chan_del, >> we can still wrap the calls to sco_conn_lock in sco_chan_del, with >> local_bh_disable/enable as this pair of functions are reentrant. >> >> Reported-by: syzbot+2f6d7c28bb4bf7e82060@syzkaller.appspotmail.com >> Tested-by: syzbot+2f6d7c28bb4bf7e82060@syzkaller.appspotmail.com >> Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com> >> --- >> net/bluetooth/sco.c | 21 +++++++++++++++++++++ >> 1 file changed, 21 insertions(+) >> >> diff --git a/net/bluetooth/sco.c b/net/bluetooth/sco.c >> index 3bd41563f118..34f3419c3330 100644 >> --- a/net/bluetooth/sco.c >> +++ b/net/bluetooth/sco.c >> @@ -140,10 +140,12 @@ static void sco_chan_del(struct sock *sk, int err) >> BT_DBG("sk %p, conn %p, err %d", sk, conn, err); >> >> if (conn) { >> + local_bh_disable(); >> sco_conn_lock(conn); >> conn->sk = NULL; >> sco_pi(sk)->conn = NULL; >> sco_conn_unlock(conn); >> + local_bh_enable(); >> >> if (conn->hcon) >> hci_conn_drop(conn->hcon); >> @@ -167,16 +169,22 @@ 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 +210,7 @@ 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 +218,7 @@ 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 +313,11 @@ 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; >> @@ -420,10 +432,12 @@ 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); >> + local_bh_enable(); >> } else >> sco_chan_del(sk, ECONNRESET); >> break; >> @@ -1084,21 +1098,26 @@ 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 +1128,7 @@ 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 +1151,7 @@ static void sco_conn_ready(struct sco_conn *conn) >> bh_unlock_sock(parent); >> >> sco_conn_unlock(conn); >> + local_bh_enable(); >> } >> } >> >> -- >> 2.25.1 >> > >
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