[PATCH 2/4] Bluetooth: L2CAP: CoC: Disconnect if received packet size exceeds MPS

[Christian Eggers <ceggers@arri.de>]

Core 6.0, Vol 3, Part A, 3.4.3:
"... If the payload size of any K-frame exceeds the receiver's MPS, the
receiver shall disconnect the channel..."

This fixes L2CAP/LE/CFC/BV-27-C (running together with 'l2test -r -P
0x0027 -V le_public -I 100').

Signed-off-by: Christian Eggers <ceggers@arri.de>
---
Maybe the naming of 'mps_orig_le' could be improved...

 include/net/bluetooth/l2cap.h | 1 +
 net/bluetooth/l2cap_core.c    | 4 +++-
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/include/net/bluetooth/l2cap.h b/include/net/bluetooth/l2cap.h
index 010f1a8fd15f..c6744cce75b1 100644
--- a/include/net/bluetooth/l2cap.h
+++ b/include/net/bluetooth/l2cap.h
@@ -552,6 +552,7 @@ struct l2cap_chan {
 	__u16		retrans_timeout;
 	__u16		monitor_timeout;
 	__u16		mps;
+	__u16		mps_orig_le;
 
 	__u16		tx_credits;
 	__u16		rx_credits;
diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
index ddac5b9270bf..c9555b0a3461 100644
--- a/net/bluetooth/l2cap_core.c
+++ b/net/bluetooth/l2cap_core.c
@@ -568,6 +568,7 @@ static void l2cap_le_flowctl_init(struct l2cap_chan *chan, u16 tx_credits)
 	chan->tx_credits = tx_credits;
 	/* Derive MPS from connection MTU to stop HCI fragmentation */
 	chan->mps = min_t(u16, chan->imtu, chan->conn->mtu - L2CAP_HDR_SIZE);
+	chan->mps_orig_le = chan->mps;
 	chan->rx_credits = l2cap_le_rx_credits(chan);
 
 	skb_queue_head_init(&chan->tx_q);
@@ -580,6 +581,7 @@ static void l2cap_ecred_init(struct l2cap_chan *chan, u16 tx_credits)
 	/* L2CAP implementations shall support a minimum MPS of 64 octets */
 	if (chan->mps < L2CAP_ECRED_MIN_MPS) {
 		chan->mps = L2CAP_ECRED_MIN_MPS;
+		chan->mps_orig_le = L2CAP_ECRED_MIN_MPS;
 		chan->rx_credits = l2cap_le_rx_credits(chan);
 	}
 }
@@ -6662,7 +6664,7 @@ static int l2cap_ecred_data_rcv(struct l2cap_chan *chan, struct sk_buff *skb)
 		return -ENOBUFS;
 	}
 
-	if (chan->imtu < skb->len) {
+	if (chan->mps_orig_le < skb->len || chan->imtu < skb->len) {
 		BT_ERR("Too big LE L2CAP PDU");
 		l2cap_send_disconn_req(chan, ECONNRESET);
 		return -ENOBUFS;
-- 
2.44.4