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Commit abe84903 authored by Johan Hedberg's avatar Johan Hedberg Committed by Marcel Holtmann
Browse files

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: default avatarJohan Hedberg <johan.hedberg@intel.com>
Signed-off-by: default avatarMarcel Holtmann <marcel@holtmann.org>
parent 24ccb9f4

include/net/bluetooth/l2cap.h

+14 −1
Original line number Diff line number Diff line
@@ -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)

net/bluetooth/l2cap_sock.c

+9 −0
Original line number Diff line number Diff line
@@ -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;

net/bluetooth/smp.c

+10 −0
Original line number Diff line number Diff line
@@ -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;