Bluetooth: Use proper nesting annotation for l2cap_chan lock

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@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

diff --git a/include/net/bluetooth/l2cap.h b/include/net/bluetooth/l2cap.h
index ead99f0..061e648 100644 (file)
--- 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 ad1cf82..f1a5156 100644 (file)
--- 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 3d38553..3b63c7f 100644 (file)
--- 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;