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Date: Wed, 21 Jul 2021 17:38:31 +0800
From: Desmond Cheong Zhi Xi <desmondcheongzx@...il.com>
To: marcel@...tmann.org, johan.hedberg@...il.com, luiz.dentz@...il.com,
davem@...emloft.net, kuba@...nel.org, matthieu.baerts@...sares.net,
stefan@...enfreihafen.org
Cc: Desmond Cheong Zhi Xi <desmondcheongzx@...il.com>,
linux-bluetooth@...r.kernel.org, netdev@...r.kernel.org,
linux-kernel@...r.kernel.org, skhan@...uxfoundation.org,
gregkh@...uxfoundation.org,
linux-kernel-mentees@...ts.linuxfoundation.org,
syzbot+2f6d7c28bb4bf7e82060@...kaller.appspotmail.com
Subject: [PATCH v3 1/2] 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 ***
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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