ksmbd: fix slub overflow in ksmbd_decode_ntlmssp_auth_blob()

A buffer overflow vulnerability in ksmbd's NTLM authentication code allows an attacker to write more data than allocated when processing oversized session keys, potentially corrupting kernel memory.

CVE-2023-52440 is a heap buffer overflow in ksmbd_decode_ntlmssp_auth_blob() where insufficient validation of authblob->SessionKey.Length permits writing beyond the CIFS_KEY_SIZE buffer during ARC4 cipher operations. The vulnerability requires an attacker to control NTLM authentication messages sent to the SMB server, and can lead to kernel memory corruption or privilege escalation.