AES-GCM-SIV copies the caller-supplied IV or nonce into its
internal state using a copy whose length is taken from the expected nonce size
rather than from the length the caller actually provided. When the caller
passes a shorter IV, the copy reads past the end of the caller's buffer;
AddressSanitizer confirms a heap out-of-bounds read reached through
EVP_CipherInit_ex() into ossl_aes_gcm_siv_init(). When the caller passes a
longer IV, the implementation silently discards the trailing bytes instead of
rejecting the length.