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

In the Linux kernel, the following vulnerability has been resolved:

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.