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[fipslegacy-8.6] Bluetooth: L2CAP: Fix use-after-free caused by l2cap_reassemble_sdu #354

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Merged
merged 1 commit into from
Jun 23, 2025
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[fipslegacy-8.6] Bluetooth: L2CAP: Fix use-after-free caused by l2cap_reassemble_sdu #354

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48 changes: 41 additions & 7 deletions net/bluetooth/l2cap_core.c
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Original file line number Diff line number Diff line change
Expand Up @@ -6867,6 +6867,7 @@ static int l2cap_rx_state_recv(struct l2cap_chan *chan,
struct l2cap_ctrl *control,
struct sk_buff *skb, u8 event)
{
struct l2cap_ctrl local_control;
int err = 0;
bool skb_in_use = false;

Expand All @@ -6891,15 +6892,32 @@ static int l2cap_rx_state_recv(struct l2cap_chan *chan,
chan->buffer_seq = chan->expected_tx_seq;
skb_in_use = true;

/* l2cap_reassemble_sdu may free skb, hence invalidate
* control, so make a copy in advance to use it after
* l2cap_reassemble_sdu returns and to avoid the race
* condition, for example:
*
* The current thread calls:
* l2cap_reassemble_sdu
* chan->ops->recv == l2cap_sock_recv_cb
* __sock_queue_rcv_skb
* Another thread calls:
* bt_sock_recvmsg
* skb_recv_datagram
* skb_free_datagram
* Then the current thread tries to access control, but
* it was freed by skb_free_datagram.
*/
local_control = *control;
err = l2cap_reassemble_sdu(chan, skb, control);
if (err)
break;

if (control->final) {
if (local_control.final) {
if (!test_and_clear_bit(CONN_REJ_ACT,
&chan->conn_state)) {
control->final = 0;
l2cap_retransmit_all(chan, control);
local_control.final = 0;
l2cap_retransmit_all(chan, &local_control);
l2cap_ertm_send(chan);
}
}
Expand Down Expand Up @@ -7279,11 +7297,27 @@ static int l2cap_rx(struct l2cap_chan *chan, struct l2cap_ctrl *control,
static int l2cap_stream_rx(struct l2cap_chan *chan, struct l2cap_ctrl *control,
struct sk_buff *skb)
{
/* l2cap_reassemble_sdu may free skb, hence invalidate control, so store
* the txseq field in advance to use it after l2cap_reassemble_sdu
* returns and to avoid the race condition, for example:
*
* The current thread calls:
* l2cap_reassemble_sdu
* chan->ops->recv == l2cap_sock_recv_cb
* __sock_queue_rcv_skb
* Another thread calls:
* bt_sock_recvmsg
* skb_recv_datagram
* skb_free_datagram
* Then the current thread tries to access control, but it was freed by
* skb_free_datagram.
*/
u16 txseq = control->txseq;

BT_DBG("chan %p, control %p, skb %p, state %d", chan, control, skb,
chan->rx_state);

if (l2cap_classify_txseq(chan, control->txseq) ==
L2CAP_TXSEQ_EXPECTED) {
if (l2cap_classify_txseq(chan, txseq) == L2CAP_TXSEQ_EXPECTED) {
l2cap_pass_to_tx(chan, control);

BT_DBG("buffer_seq %u->%u", chan->buffer_seq,
Expand All @@ -7306,8 +7340,8 @@ static int l2cap_stream_rx(struct l2cap_chan *chan, struct l2cap_ctrl *control,
}
}

chan->last_acked_seq = control->txseq;
chan->expected_tx_seq = __next_seq(chan, control->txseq);
chan->last_acked_seq = txseq;
chan->expected_tx_seq = __next_seq(chan, txseq);

return 0;
}
Expand Down