ksmbd: fix multiple out-of-bounds read during context decoding

ksmbd: fix multiple out-of-bounds read during context decoding

commit 0512a5f89e1fae74251fde6893ff634f1c96c6fb upstream.

Check the remaining data length before accessing the context structure
to ensure that the entire structure is contained within the packet.
Additionally, since the context data length `ctxt_len` has already been
checked against the total packet length `len_of_ctxts`, update the
comparison to use `ctxt_len`.

Cc: stable@vger.kernel.org
Signed-off-by: Kuan-Ting Chen <h3xrabbit@gmail.com>
Acked-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>