From: Johan Hedberg <johan.hedberg@xxxxxxxxx>
By default lockdep considers all L2CAP channels equal. This would mean
that we get warnings if a channel is locked when another one's lock is
tried to be acquired in the same thread. This kind of inter-channel
locking dependencies exist in the form of parent-child channels as well
as any channel wishing to elevate the security by requesting procedures
on the SMP channel.
To eliminate the chance for these lockdep warnings we introduce a
nesting level for each channel and use that when acquiring the channel
lock. For now there exists the earlier mentioned three identified
categories: SMP, "normal" channels and parent channels (i.e. those in
BT_LISTEN state). The nesting level is defined as atomic_t since we need
access to it before the lock is actually acquired.
Signed-off-by: Johan Hedberg <johan.hedberg@xxxxxxxxx>
---
include/net/bluetooth/l2cap.h | 15 ++++++++++++++-
net/bluetooth/l2cap_sock.c | 9 +++++++++
net/bluetooth/smp.c | 10 ++++++++++
3 files changed, 33 insertions(+), 1 deletion(-)
diff --git a/include/net/bluetooth/l2cap.h b/include/net/bluetooth/l2cap.h
index ead99f032f7a..061e648052c8 100644
--- a/include/net/bluetooth/l2cap.h
+++ b/include/net/bluetooth/l2cap.h
@@ -28,6 +28,7 @@
#define __L2CAP_H
#include <asm/unaligned.h>
+#include <linux/atomic.h>
/* L2CAP defaults */
#define L2CAP_DEFAULT_MTU 672
@@ -481,6 +482,7 @@ struct l2cap_chan {
struct hci_conn *hs_hcon;
struct hci_chan *hs_hchan;
struct kref kref;
+ atomic_t nesting;
__u8 state;
@@ -713,6 +715,17 @@ enum {
FLAG_HOLD_HCI_CONN,
};
+/* Lock nesting levels for L2CAP channels. We need these because lockdep
+ * otherwise considers all channels equal and will e.g. complain about a
+ * connection oriented channel triggering SMP procedures or a listening
+ * channel creating and locking a child channel.
+ */
+enum {
+ L2CAP_NESTING_SMP,
+ L2CAP_NESTING_NORMAL,
+ L2CAP_NESTING_PARENT,
+};
+
enum {
L2CAP_TX_STATE_XMIT,
L2CAP_TX_STATE_WAIT_F,
@@ -778,7 +791,7 @@ void l2cap_chan_put(struct l2cap_chan *c);
static inline void l2cap_chan_lock(struct l2cap_chan *chan)
{
- mutex_lock(&chan->lock);
+ mutex_lock_nested(&chan->lock, atomic_read(&chan->nesting));
}
static inline void l2cap_chan_unlock(struct l2cap_chan *chan)
diff --git a/net/bluetooth/l2cap_sock.c b/net/bluetooth/l2cap_sock.c
index ad1cf82fee02..f1a51564b8fd 100644
--- a/net/bluetooth/l2cap_sock.c
+++ b/net/bluetooth/l2cap_sock.c
@@ -285,6 +285,12 @@ static int l2cap_sock_listen(struct socket *sock, int backlog)
sk->sk_max_ack_backlog = backlog;
sk->sk_ack_backlog = 0;
+ /* Listening channels need to use nested locking in order not to
+ * cause lockdep warnings when the created child channels end up
+ * being locked in the same thread as the parent channel.
+ */
+ atomic_set(&chan->nesting, L2CAP_NESTING_PARENT);
+
chan->state = BT_LISTEN;
sk->sk_state = BT_LISTEN;
@@ -1497,6 +1503,9 @@ static void l2cap_sock_init(struct sock *sk, struct sock *parent)
l2cap_chan_set_defaults(chan);
}
+ /* Set default lock nesting level */
+ atomic_set(&chan->nesting, L2CAP_NESTING_NORMAL);
+
/* Default config options */
chan->flush_to = L2CAP_DEFAULT_FLUSH_TO;
diff --git a/net/bluetooth/smp.c b/net/bluetooth/smp.c
index 3d38553eb526..3b63c7f09dd5 100644
--- a/net/bluetooth/smp.c
+++ b/net/bluetooth/smp.c
@@ -1658,6 +1658,13 @@ static inline struct l2cap_chan *smp_new_conn_cb(struct l2cap_chan *pchan)
chan->omtu = pchan->omtu;
chan->mode = pchan->mode;
+ /* Other L2CAP channels may request SMP routines in order to
+ * change the security level. This means that the SMP channel
+ * lock must be considered in its own category to avoid lockdep
+ * warnings.
+ */
+ atomic_set(&chan->nesting, L2CAP_NESTING_SMP);
+
BT_DBG("created chan %p", chan);
return chan;
@@ -1715,6 +1722,9 @@ int smp_register(struct hci_dev *hdev)
chan->imtu = L2CAP_DEFAULT_MTU;
chan->ops = &smp_root_chan_ops;
+ /* Set correct nesting level for a parent/listening channel */
+ atomic_set(&chan->nesting, L2CAP_NESTING_PARENT);
+
hdev->smp_data = chan;
return 0;
--
2.1.0
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