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Bluetooth: Fix race condition on l2cap_ertm_send()
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l2cap_ertm_send() can be called both from user context and bottom half
context. The socket locks for that contexts are different, the user
context uses a mutex(which can sleep) and the second one uses a
spinlock_bh. That creates a race condition when we have interruptions on
both contexts at the same time.

The better way to solve this is to add a new spinlock to lock
l2cap_ertm_send() and the vars it access. The other solution was to defer
l2cap_ertm_send() with a workqueue, but we the sending process already
has one defer on the hci layer. It's not a good idea add another one.

The patch refactor the code to create l2cap_retransmit_frames(), then we
encapulate the lock of l2cap_ertm_send() for some call. It also changes
l2cap_retransmit_frame() to l2cap_retransmit_one_frame() to avoid
confusion

Signed-off-by: Gustavo F. Padovan <padovan@profusion.mobi>
Reviewed-by: João Paulo Rechi Vita <jprvita@profusion.mobi>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
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Gustavo F. Padovan authored and Marcel Holtmann committed May 10, 2010
1 parent 6161c03 commit dfc909b
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Showing 2 changed files with 67 additions and 33 deletions.
1 change: 1 addition & 0 deletions include/net/bluetooth/l2cap.h
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Original file line number Diff line number Diff line change
Expand Up @@ -353,6 +353,7 @@ struct l2cap_pinfo {

__le16 sport;

spinlock_t send_lock;
struct timer_list retrans_timer;
struct timer_list monitor_timer;
struct timer_list ack_timer;
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99 changes: 66 additions & 33 deletions net/bluetooth/l2cap.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -1368,7 +1368,7 @@ static int l2cap_streaming_send(struct sock *sk)
return 0;
}

static void l2cap_retransmit_frame(struct sock *sk, u8 tx_seq)
static void l2cap_retransmit_one_frame(struct sock *sk, u8 tx_seq)
{
struct l2cap_pinfo *pi = l2cap_pi(sk);
struct sk_buff *skb, *tx_skb;
Expand Down Expand Up @@ -1467,10 +1467,29 @@ static int l2cap_ertm_send(struct sock *sk)
return nsent;
}

static int l2cap_retransmit_frames(struct sock *sk)
{
struct l2cap_pinfo *pi = l2cap_pi(sk);
int ret;

spin_lock_bh(&pi->send_lock);

if (!skb_queue_empty(TX_QUEUE(sk)))
sk->sk_send_head = TX_QUEUE(sk)->next;

pi->next_tx_seq = pi->expected_ack_seq;
ret = l2cap_ertm_send(sk);

spin_unlock_bh(&pi->send_lock);

return ret;
}

static void l2cap_send_ack(struct l2cap_pinfo *pi)
{
struct sock *sk = (struct sock *)pi;
u16 control = 0;
int nframes;

control |= pi->buffer_seq << L2CAP_CTRL_REQSEQ_SHIFT;

Expand All @@ -1479,10 +1498,17 @@ static void l2cap_send_ack(struct l2cap_pinfo *pi)
pi->conn_state |= L2CAP_CONN_RNR_SENT;
l2cap_send_sframe(pi, control);
return;
} else if (l2cap_ertm_send(sk) == 0) {
control |= L2CAP_SUPER_RCV_READY;
l2cap_send_sframe(pi, control);
}

spin_lock_bh(&pi->send_lock);
nframes = l2cap_ertm_send(sk);
spin_unlock_bh(&pi->send_lock);

if (nframes > 0)
return;

control |= L2CAP_SUPER_RCV_READY;
l2cap_send_sframe(pi, control);
}

static void l2cap_send_srejtail(struct sock *sk)
Expand Down Expand Up @@ -1673,8 +1699,10 @@ static inline int l2cap_sar_segment_sdu(struct sock *sk, struct msghdr *msg, siz
size += buflen;
}
skb_queue_splice_tail(&sar_queue, TX_QUEUE(sk));
spin_lock_bh(&pi->send_lock);
if (sk->sk_send_head == NULL)
sk->sk_send_head = sar_queue.next;
spin_unlock_bh(&pi->send_lock);

return size;
}
Expand Down Expand Up @@ -1745,19 +1773,29 @@ static int l2cap_sock_sendmsg(struct kiocb *iocb, struct socket *sock, struct ms
goto done;
}
__skb_queue_tail(TX_QUEUE(sk), skb);

if (pi->mode == L2CAP_MODE_ERTM)
spin_lock_bh(&pi->send_lock);

if (sk->sk_send_head == NULL)
sk->sk_send_head = skb;

if (pi->mode == L2CAP_MODE_ERTM)
spin_unlock_bh(&pi->send_lock);
} else {
/* Segment SDU into multiples PDUs */
err = l2cap_sar_segment_sdu(sk, msg, len);
if (err < 0)
goto done;
}

if (pi->mode == L2CAP_MODE_STREAMING)
if (pi->mode == L2CAP_MODE_STREAMING) {
err = l2cap_streaming_send(sk);
else
} else {
spin_lock_bh(&pi->send_lock);
err = l2cap_ertm_send(sk);
spin_unlock_bh(&pi->send_lock);
}

if (err >= 0)
err = len;
Expand Down Expand Up @@ -2321,6 +2359,7 @@ static inline void l2cap_ertm_init(struct sock *sk)

__skb_queue_head_init(SREJ_QUEUE(sk));
__skb_queue_head_init(BUSY_QUEUE(sk));
spin_lock_init(&l2cap_pi(sk)->send_lock);

INIT_WORK(&l2cap_pi(sk)->busy_work, l2cap_busy_work);
}
Expand Down Expand Up @@ -3340,7 +3379,9 @@ static inline void l2cap_send_i_or_rr_or_rnr(struct sock *sk)
if (pi->conn_state & L2CAP_CONN_REMOTE_BUSY && pi->unacked_frames > 0)
__mod_retrans_timer();

spin_lock_bh(&pi->send_lock);
l2cap_ertm_send(sk);
spin_unlock_bh(&pi->send_lock);

if (!(pi->conn_state & L2CAP_CONN_LOCAL_BUSY) &&
pi->frames_sent == 0) {
Expand Down Expand Up @@ -3857,12 +3898,8 @@ static inline int l2cap_data_channel_iframe(struct sock *sk, u16 rx_control, str
if (rx_control & L2CAP_CTRL_FINAL) {
if (pi->conn_state & L2CAP_CONN_REJ_ACT)
pi->conn_state &= ~L2CAP_CONN_REJ_ACT;
else {
if (!skb_queue_empty(TX_QUEUE(sk)))
sk->sk_send_head = TX_QUEUE(sk)->next;
pi->next_tx_seq = pi->expected_ack_seq;
l2cap_ertm_send(sk);
}
else
l2cap_retransmit_frames(sk);
}

err = l2cap_push_rx_skb(sk, skb, rx_control);
Expand Down Expand Up @@ -3907,23 +3944,22 @@ static inline void l2cap_data_channel_rrframe(struct sock *sk, u16 rx_control)

if (pi->conn_state & L2CAP_CONN_REJ_ACT)
pi->conn_state &= ~L2CAP_CONN_REJ_ACT;
else {
if (!skb_queue_empty(TX_QUEUE(sk)))
sk->sk_send_head = TX_QUEUE(sk)->next;
pi->next_tx_seq = pi->expected_ack_seq;
l2cap_ertm_send(sk);
}
else
l2cap_retransmit_frames(sk);

} else {
if ((pi->conn_state & L2CAP_CONN_REMOTE_BUSY) &&
(pi->unacked_frames > 0))
__mod_retrans_timer();

pi->conn_state &= ~L2CAP_CONN_REMOTE_BUSY;
if (pi->conn_state & L2CAP_CONN_SREJ_SENT)
if (pi->conn_state & L2CAP_CONN_SREJ_SENT) {
l2cap_send_ack(pi);
else
} else {
spin_lock_bh(&pi->send_lock);
l2cap_ertm_send(sk);
spin_unlock_bh(&pi->send_lock);
}
}
}

Expand All @@ -3940,17 +3976,10 @@ static inline void l2cap_data_channel_rejframe(struct sock *sk, u16 rx_control)
if (rx_control & L2CAP_CTRL_FINAL) {
if (pi->conn_state & L2CAP_CONN_REJ_ACT)
pi->conn_state &= ~L2CAP_CONN_REJ_ACT;
else {
if (!skb_queue_empty(TX_QUEUE(sk)))
sk->sk_send_head = TX_QUEUE(sk)->next;
pi->next_tx_seq = pi->expected_ack_seq;
l2cap_ertm_send(sk);
}
else
l2cap_retransmit_frames(sk);
} else {
if (!skb_queue_empty(TX_QUEUE(sk)))
sk->sk_send_head = TX_QUEUE(sk)->next;
pi->next_tx_seq = pi->expected_ack_seq;
l2cap_ertm_send(sk);
l2cap_retransmit_frames(sk);

if (pi->conn_state & L2CAP_CONN_WAIT_F)
pi->conn_state |= L2CAP_CONN_REJ_ACT;
Expand All @@ -3966,8 +3995,12 @@ static inline void l2cap_data_channel_srejframe(struct sock *sk, u16 rx_control)
if (rx_control & L2CAP_CTRL_POLL) {
pi->expected_ack_seq = tx_seq;
l2cap_drop_acked_frames(sk);
l2cap_retransmit_frame(sk, tx_seq);
l2cap_retransmit_one_frame(sk, tx_seq);

spin_lock_bh(&pi->send_lock);
l2cap_ertm_send(sk);
spin_unlock_bh(&pi->send_lock);

if (pi->conn_state & L2CAP_CONN_WAIT_F) {
pi->srej_save_reqseq = tx_seq;
pi->conn_state |= L2CAP_CONN_SREJ_ACT;
Expand All @@ -3977,9 +4010,9 @@ static inline void l2cap_data_channel_srejframe(struct sock *sk, u16 rx_control)
pi->srej_save_reqseq == tx_seq)
pi->conn_state &= ~L2CAP_CONN_SREJ_ACT;
else
l2cap_retransmit_frame(sk, tx_seq);
l2cap_retransmit_one_frame(sk, tx_seq);
} else {
l2cap_retransmit_frame(sk, tx_seq);
l2cap_retransmit_one_frame(sk, tx_seq);
if (pi->conn_state & L2CAP_CONN_WAIT_F) {
pi->srej_save_reqseq = tx_seq;
pi->conn_state |= L2CAP_CONN_SREJ_ACT;
Expand Down

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