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Message-ID: <764e18f7-ccf4-2010-87fc-feb1d3089098@gmail.com>
Date: Tue, 27 Jul 2021 13:13:27 +0800
From: Desmond Cheong Zhi Xi <desmondcheongzx@...il.com>
To: Luiz Augusto von Dentz <luiz.dentz@...il.com>
Cc: Marcel Holtmann <marcel@...tmann.org>,
Johan Hedberg <johan.hedberg@...il.com>,
David Miller <davem@...emloft.net>,
Jakub Kicinski <kuba@...nel.org>, matthieu.baerts@...sares.net,
stefan@...enfreihafen.org,
"linux-bluetooth@...r.kernel.org" <linux-bluetooth@...r.kernel.org>,
"open list:NETWORKING [GENERAL]" <netdev@...r.kernel.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
skhan@...uxfoundation.org,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
linux-kernel-mentees@...ts.linuxfoundation.org,
syzbot+2f6d7c28bb4bf7e82060@...kaller.appspotmail.com
Subject: Re: [PATCH v3 1/2] Bluetooth: fix inconsistent lock state in SCO
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@...il.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@...kaller.appspotmail.com
>> Tested-by: syzbot+2f6d7c28bb4bf7e82060@...kaller.appspotmail.com
>> Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@...il.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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