[PATCH 5.15 332/570] Bluetooth: L2CAP: Fix ERTM re-init and zero pdu_len infinite loop

Greg Kroah-Hartman
2026-04-13T16:33:06Z

From: Hyunwoo Kim <imv4bel@gmail.com>

[ Upstream commit 25f420a0d4cfd61d3d23ec4b9c56d9f443d91377 ]

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: 96298f640104 ("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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/bluetooth/l2cap_core.c | 19 ++++++++++++-------
1 file changed, 12 insertions(+), 7 deletions(-)

diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
index e69c6041437b0..ef71a43ab702d 100644
--- a/net/bluetooth/l2cap_core.c
+++ b/net/bluetooth/l2cap_core.c
@@ -2541,6 +2541,9 @@ 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;
@@ -4515,14 +4518,16 @@ 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->mode == L2CAP_MODE_ERTM ||
- chan->mode == L2CAP_MODE_STREAMING)
- err = l2cap_ertm_init(chan);
+ if (chan->state != BT_CONNECTED) {
+ if (chan->mode == L2CAP_MODE_ERTM ||
+ chan->mode == L2CAP_MODE_STREAMING)
+ err = l2cap_ertm_init(chan);

- if (err < 0)
- l2cap_send_disconn_req(chan, -err);
- else
- l2cap_chan_ready(chan);
+ if (err < 0)
+ l2cap_send_disconn_req(chan, -err);
+ else
+ l2cap_chan_ready(chan);
+ }

goto unlock;
}
--
2.51.0