[PATCH] Bluetooth: l2cap: fix MPS check in l2cap_ecred_reconf_req

Dudu Lu
2026-04-15T10:44:01Z

The L2CAP specification states that if more than one channel is being
reconfigured, the MPS shall not be decreased. The current check has
two issues:

1) The comparison uses >= (greater-than-or-equal), which incorrectly
rejects reconfiguration requests where the MPS stays the same.
Since the spec says MPS "shall be greater than or equal to the
current MPS", only a strict decrease (remote_mps > mps) should be
rejected. Keeping the same MPS is valid.

2) The multi-channel guard uses `&& i` (loop index) to approximate
"more than one channel", but this incorrectly allows MPS decrease
for the first channel (i==0) even when multiple channels are being
reconfigured. Replace with `&& num_scid > 1` which correctly
checks whether the request covers more than one channel.

Signed-off-by: Dudu Lu <phx0fer@gmail.com>
---
net/bluetooth/l2cap_core.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
index 95c65fece39b..29d793f3a2eb 100644
--- a/net/bluetooth/l2cap_core.c
+++ b/net/bluetooth/l2cap_core.c
@@ -5428,7 +5428,7 @@ static inline int l2cap_ecred_reconf_req(struct l2cap_conn *conn,
* configured, the MPS field may be less than the current MPS
* of that channel.
*/
- if (chan[i]->remote_mps >= mps && i) {
+ if (chan[i]->remote_mps > mps && num_scid > 1) {
BT_ERR("chan %p decreased MPS %u -> %u", chan[i],
chan[i]->remote_mps, mps);
result = L2CAP_RECONF_INVALID_MPS;
--
2.39.3 (Apple Git-145)