Bluetooth: L2CAP: Validate PDU length before reading SDU length in l2cap_ecred_data_rcv()

l2cap_ecred_data_rcv() reads the SDU length field from skb->data using
get_unaligned_le16() without first verifying that skb contains at least
L2CAP_SDULEN_SIZE (2) bytes. When skb->len is less than 2, this reads
past the valid data in the skb.

The ERTM reassembly path correctly calls pskb_may_pull() before reading
the SDU length (l2cap_reassemble_sdu, L2CAP_SAR_START case). Apply the
same validation to the Enhanced Credit Based Flow Control data path.

Fixes: aac23bf ("Bluetooth: Implement LE L2CAP reassembly")
Signed-off-by: Hyunwoo Kim <[email protected]>
Signed-off-by: Luiz Augusto von Dentz <[email protected]>

Author: V4bel

net/bluetooth/l2cap_core.c

@@ -6690,6 +6690,11 @@ static int l2cap_ecred_data_rcv(struct l2cap_chan *chan, struct sk_buff *skb)
 	if (!chan->sdu) {
 		u16 sdu_len;
 
+		if (!pskb_may_pull(skb, L2CAP_SDULEN_SIZE)) {
+			err = -EINVAL;
+			goto failed;
+		}
+
 		sdu_len = get_unaligned_le16(skb->data);
 		skb_pull(skb, L2CAP_SDULEN_SIZE);