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Date: Thu, 15 Jul 2021 10:21:42 +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>, 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 v2] Bluetooth: fix inconsistent lock state in sco
On 15/7/21 3:12 am, Luiz Augusto von Dentz wrote:
> Hi Desmond,
>
> On Tue, Jul 13, 2021 at 9:29 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);
>>
>> *** 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@...kaller.appspotmail.com
>> Tested-by: syzbot+2f6d7c28bb4bf7e82060@...kaller.appspotmail.com
>> Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@...il.com>
>> ---
>>
>> 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.
>
Thanks for the feedback, Luiz. I'll separate the SCO and RFCOMM code
changes.
I believe other sockets should be fine. From what I see, they use
lock_sock, which acquires the spin lock via spin_lock_bh under the hood.
So only code that uses bh_lock_sock/bh_lock_sock_nested are affected.
Also I'm not sure what you meant by going with local_bh_disable? I'm
probably missing context about Bluetooth protocols, but I think the spin
locks still have their place to protect concurrent accesses and to make
it clear about what's being protected.
>> 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
>>
>
>
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