Re: [PATCH v2] Bluetooth: fix inconsistent lock state in sco
From: Desmond Cheong Zhi Xi
Date: Wed Jul 14 2021 - 22:21:53 EST
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@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.
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