Umbraco-CMS/src/Umbraco.Core/Configuration/ModelsBuilderConfigExtensions.cs

using System.IO;
using Umbraco.Cms.Core.Configuration.Models;
using Umbraco.Cms.Core.Exceptions;
using Umbraco.Cms.Core.Hosting;

namespace Umbraco.Extensions
{
    public static class ModelsBuilderConfigExtensions
    {
        private static string _modelsDirectoryAbsolute = null;

        public static string ModelsDirectoryAbsolute(this ModelsBuilderSettings modelsBuilderConfig, IHostingEnvironment hostingEnvironment)
        {
            if (_modelsDirectoryAbsolute is null)
            {
                var modelsDirectory = modelsBuilderConfig.ModelsDirectory;
                var root = hostingEnvironment.MapPathContentRoot("~/");

                _modelsDirectoryAbsolute = GetModelsDirectory(root, modelsDirectory,
                    modelsBuilderConfig.AcceptUnsafeModelsDirectory);
            }

            return _modelsDirectoryAbsolute;
        }

        // internal for tests
        internal static string GetModelsDirectory(string root, string config, bool acceptUnsafe)
        {
            // making sure it is safe, ie under the website root,
            // unless AcceptUnsafeModelsDirectory and then everything is OK.

            if (!Path.IsPathRooted(root))
                throw new ConfigurationException($"Root is not rooted \"{root}\".");

            if (config.StartsWith("~/"))
            {
                var dir = Path.Combine(root, config.TrimStart("~/"));

                // sanitize - GetFullPath will take care of any relative
                // segments in path, eg '../../foo.tmp' - it may throw a SecurityException
                // if the combined path reaches illegal parts of the filesystem
                dir = Path.GetFullPath(dir);
                root = Path.GetFullPath(root);

                if (!dir.StartsWith(root) && !acceptUnsafe)
                    throw new ConfigurationException($"Invalid models directory \"{config}\".");

                return dir;
            }

            if (acceptUnsafe)
                return Path.GetFullPath(config);

            throw new ConfigurationException($"Invalid models directory \"{config}\".");
        }
    }
}