Commit 25f420a0 authored Mar 20, 2026 by Hyunwoo Kim Committed by Luiz Augusto von Dentz Mar 25, 2026

Bluetooth: L2CAP: Fix ERTM re-init and zero pdu_len infinite loop

l2cap_config_req() processes CONFIG_REQ for channels in BT_CONNECTED
state to support L2CAP reconfiguration (e.g. MTU changes). However,
since both CONF_INPUT_DONE and CONF_OUTPUT_DONE are already set from
the initial configuration, the reconfiguration path falls through to
l2cap_ertm_init(), which re-initializes tx_q, srej_q, srej_list, and
retrans_list without freeing the previous allocations and sets
chan->sdu to NULL without freeing the existing skb. This leaks all
previously allocated ERTM resources.

Additionally, l2cap_parse_conf_req() does not validate the minimum
value of remote_mps derived from the RFC max_pdu_size option. A zero
value propagates to l2cap_segment_sdu() where pdu_len becomes zero,
causing the while loop to never terminate since len is never
decremented, exhausting all available memory.

Fix the double-init by skipping l2cap_ertm_init() and
l2cap_chan_ready() when the channel is already in BT_CONNECTED state,
while still allowing the reconfiguration parameters to be updated
through l2cap_parse_conf_req(). Also add a pdu_len zero check in
l2cap_segment_sdu() as a safeguard.

Fixes: 96298f64 ("Bluetooth: L2CAP: handle l2cap config request during open state")
Signed-off-by: Hyunwoo Kim <imv4bel@gmail.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>

parent 00fdebbb

net/bluetooth/l2cap_core.c

+12 −7

Original line number	Diff line number	Diff line
		@@ -2398,6 +2398,9 @@ static int l2cap_segment_sdu(struct l2cap_chan *chan,
		/* Remote device may have requested smaller PDUs */
		pdu_len = min_t(size_t, pdu_len, chan->remote_mps);

		if (!pdu_len)
		return -EINVAL;

		if (len <= pdu_len) {
		sar = L2CAP_SAR_UNSEGMENTED;
		sdu_len = 0;
		@@ -4333,6 +4336,7 @@ static inline int l2cap_config_req(struct l2cap_conn *conn,
		if (test_bit(CONF_INPUT_DONE, &chan->conf_state)) {
		set_default_fcs(chan);

		if (chan->state != BT_CONNECTED) {
		if (chan->mode == L2CAP_MODE_ERTM \|\|
		chan->mode == L2CAP_MODE_STREAMING)
		err = l2cap_ertm_init(chan);
		@@ -4341,6 +4345,7 @@ static inline int l2cap_config_req(struct l2cap_conn *conn,
		l2cap_send_disconn_req(chan, -err);
		else
		l2cap_chan_ready(chan);
		}

		goto unlock;
		}