static int chacha20_poly1305_ctrl(EVP_CIPHER_CTX *ctx, int type, int arg,
                                  void *ptr)
{
    EVP_CHACHA_AEAD_CTX *actx = aead_data(ctx);

    switch(type) {
    case EVP_CTRL_INIT:
        if (actx == NULL)
            actx = ctx->cipher_data
                 = OPENSSL_zalloc(sizeof(*actx) + Poly1305_ctx_size());
        if (actx == NULL) {
            EVPerr(EVP_F_CHACHA20_POLY1305_CTRL, EVP_R_INITIALIZATION_ERROR);
            return 0;
        }
        actx->len.aad = 0;
        actx->len.text = 0;
        actx->aad = 0;
        actx->mac_inited = 0;
        actx->tag_len = 0;
        actx->nonce_len = 12;
        actx->tls_payload_length = NO_TLS_PAYLOAD_LENGTH;
        return 1;

    case EVP_CTRL_COPY:
        if (actx) {
            EVP_CIPHER_CTX *dst = (EVP_CIPHER_CTX *)ptr;

            dst->cipher_data =
                   OPENSSL_memdup(actx, sizeof(*actx) + Poly1305_ctx_size());
            if (dst->cipher_data == NULL) {
                EVPerr(EVP_F_CHACHA20_POLY1305_CTRL, EVP_R_COPY_ERROR);
                return 0;
            }
        }
        return 1;

    case EVP_CTRL_AEAD_SET_IVLEN:
        if (arg <= 0 || arg > CHACHA_CTR_SIZE)
            return 0;
        actx->nonce_len = arg;
        return 1;

    case EVP_CTRL_AEAD_SET_IV_FIXED:
        if (arg != 12)
            return 0;
        actx->nonce[0] = actx->key.counter[1]
                       = CHACHA_U8TOU32((unsigned char *)ptr);
        actx->nonce[1] = actx->key.counter[2]
                       = CHACHA_U8TOU32((unsigned char *)ptr+4);
        actx->nonce[2] = actx->key.counter[3]
                       = CHACHA_U8TOU32((unsigned char *)ptr+8);
        return 1;

    case EVP_CTRL_AEAD_SET_TAG:
        if (arg <= 0 || arg > POLY1305_BLOCK_SIZE)
            return 0;
        if (ptr != NULL) {
            memcpy(actx->tag, ptr, arg);
            actx->tag_len = arg;
        }
        return 1;

    case EVP_CTRL_AEAD_GET_TAG:
        if (arg <= 0 || arg > POLY1305_BLOCK_SIZE || !ctx->encrypt)
            return 0;
        memcpy(ptr, actx->tag, arg);
        return 1;

    case EVP_CTRL_AEAD_TLS1_AAD:
        if (arg != EVP_AEAD_TLS1_AAD_LEN)
            return 0;
        {
            unsigned int len;
            unsigned char *aad = ptr, temp[POLY1305_BLOCK_SIZE];

             len = aad[EVP_AEAD_TLS1_AAD_LEN - 2] << 8 |
                   aad[EVP_AEAD_TLS1_AAD_LEN - 1];
             if (!ctx->encrypt) {
                if (len < POLY1305_BLOCK_SIZE)
                    return 0;
                 len -= POLY1305_BLOCK_SIZE;     /* discount attached tag */
                 memcpy(temp, aad, EVP_AEAD_TLS1_AAD_LEN - 2);
                 aad = temp;
                temp[EVP_AEAD_TLS1_AAD_LEN - 2] = (unsigned char)(len >> 8);
                temp[EVP_AEAD_TLS1_AAD_LEN - 1] = (unsigned char)len;
            }
             actx->tls_payload_length = len;
 
             /*
             * merge record sequence number as per RFC7905
              */
             actx->key.counter[1] = actx->nonce[0];
             actx->key.counter[2] = actx->nonce[1] ^ CHACHA_U8TOU32(aad);
            actx->key.counter[3] = actx->nonce[2] ^ CHACHA_U8TOU32(aad+4);
            actx->mac_inited = 0;
            chacha20_poly1305_cipher(ctx, NULL, aad, EVP_AEAD_TLS1_AAD_LEN);
            return POLY1305_BLOCK_SIZE;         /* tag length */
        }

    case EVP_CTRL_AEAD_SET_MAC_KEY:
        /* no-op */
        return 1;

    default:
        return -1;
    }
}

The product reads data past the end, or before the beginning, of the intended buffer.