检查 .NET 中的目录和文件写入权限

Question

在我的 .NET 2.0 应用程序中，我需要检查是否存在足够的权限来创建文件并将其写入目录。 为此，我有以下函数尝试创建一个文件并向其中写入一个字节，然后删除自身以测试权限确实存在。

我认为最好的检查方法是实际尝试并执行它，捕获发生的任何异常。 不过，我对一般的异常捕获并不是特别满意，那么是否有更好或更可接受的方法来做到这一点？

private const string TEMP_FILE = "\\tempFile.tmp";

/// <summary>
/// Checks the ability to create and write to a file in the supplied directory.
/// </summary>
/// <param name="directory">String representing the directory path to check.</param>
/// <returns>True if successful; otherwise false.</returns>
private static bool CheckDirectoryAccess(string directory)
{
    bool success = false;
    string fullPath = directory + TEMP_FILE;

    if (Directory.Exists(directory))
    {
        try
        {
            using (FileStream fs = new FileStream(fullPath, FileMode.CreateNew, 
                                                            FileAccess.Write))
            {
                fs.WriteByte(0xff);
            }

            if (File.Exists(fullPath))
            {
                File.Delete(fullPath);
                success = true;
            }
        }
        catch (Exception)
        {
            success = false;
        }
    }

Answer 1

Directory.GetAccessControl(path)您的要求。

public static bool HasWritePermissionOnDir(string path)
{
    var writeAllow = false;
    var writeDeny = false;
    var accessControlList = Directory.GetAccessControl(path);
    if (accessControlList == null)
        return false;
    var accessRules = accessControlList.GetAccessRules(true, true, 
                                typeof(System.Security.Principal.SecurityIdentifier));
    if (accessRules ==null)
        return false;

    foreach (FileSystemAccessRule rule in accessRules)
    {
        if ((FileSystemRights.Write & rule.FileSystemRights) != FileSystemRights.Write) 
            continue;

        if (rule.AccessControlType == AccessControlType.Allow)
            writeAllow = true;
        else if (rule.AccessControlType == AccessControlType.Deny)
            writeDeny = true;
    }

    return writeAllow && !writeDeny;
}

(FileSystemRights.Write & rights) == FileSystemRights.Write正在使用一种叫做“Flags”的东西，顺便说一句，如果你不知道它是什么，你应该仔细阅读:)

Answer 2

Deny优先于Allow 。 本地规则优先于继承规则。 我见过很多解决方案（包括这里显示的一些答案），但没有一个考虑到规则是否被继承。 因此，我建议采用以下考虑规则继承的方法（整齐地包装到一个类中）：

public class CurrentUserSecurity
{
    WindowsIdentity _currentUser;
    WindowsPrincipal _currentPrincipal;

    public CurrentUserSecurity()
    {
        _currentUser = WindowsIdentity.GetCurrent();
        _currentPrincipal = new WindowsPrincipal(_currentUser);
    }

    public bool HasAccess(DirectoryInfo directory, FileSystemRights right)
    {
        // Get the collection of authorization rules that apply to the directory.
        AuthorizationRuleCollection acl = directory.GetAccessControl()
            .GetAccessRules(true, true, typeof(SecurityIdentifier));
        return HasFileOrDirectoryAccess(right, acl);
    }

    public bool HasAccess(FileInfo file, FileSystemRights right)
    {
        // Get the collection of authorization rules that apply to the file.
        AuthorizationRuleCollection acl = file.GetAccessControl()
            .GetAccessRules(true, true, typeof(SecurityIdentifier));
        return HasFileOrDirectoryAccess(right, acl);
    }

    private bool HasFileOrDirectoryAccess(FileSystemRights right,
                                          AuthorizationRuleCollection acl)
    {
        bool allow = false;
        bool inheritedAllow = false;
        bool inheritedDeny = false;

        for (int i = 0; i < acl.Count; i++) {
            var currentRule = (FileSystemAccessRule)acl[i];
            // If the current rule applies to the current user.
            if (_currentUser.User.Equals(currentRule.IdentityReference) ||
                _currentPrincipal.IsInRole(
                                (SecurityIdentifier)currentRule.IdentityReference)) {

                if (currentRule.AccessControlType.Equals(AccessControlType.Deny)) {
                    if ((currentRule.FileSystemRights & right) == right) {
                        if (currentRule.IsInherited) {
                            inheritedDeny = true;
                        } else { // Non inherited "deny" takes overall precedence.
                            return false;
                        }
                    }
                } else if (currentRule.AccessControlType
                                                  .Equals(AccessControlType.Allow)) {
                    if ((currentRule.FileSystemRights & right) == right) {
                        if (currentRule.IsInherited) {
                            inheritedAllow = true;
                        } else {
                            allow = true;
                        }
                    }
                }
            }
        }

        if (allow) { // Non inherited "allow" takes precedence over inherited rules.
            return true;
        }
        return inheritedAllow && !inheritedDeny;
    }
}

但是，我的经验是这并不总是适用于远程计算机，因为您并不总是有权在那里查询文件访问权限。 这种情况下的解决方案是尝试； 如果您需要在使用“真实”文件之前知道访问权限，甚至可能只是尝试创建一个临时文件。

Answer 3

理查德和杰森的答案在某种程度上是正确的。 但是，您应该做的是计算运行代码的用户身份的有效权限。 例如，上面的示例都没有正确说明组成员身份。

我很确定Keith Brown在他的The .NET Developers Guide to Windows Security 的wiki 版本（此时离线）中有一些代码可以做到这一点。 这也在他的Windows 安全编程一书中进行了合理的详细讨论。

计算有效权限不适合胆小的人，您的代码尝试创建文件并捕获抛出的安全异常可能是阻力最小的路径。

Answer 4

Kev 对这个问题的公认答案实际上并没有给出任何代码，它只是指向我无权访问的其他资源。 所以这是我对该功能的最佳尝试。 它实际上会检查它正在查看的权限是否为“写入”权限，以及当前用户是否属于适当的组。

关于网络路径或其他内容，它可能不完整，但对于我的目的来说已经足够了，检查“程序文件”下的本地配置文件的可写性：

using System.Security.Principal;
using System.Security.AccessControl;

private static bool HasWritePermission(string FilePath)
{
    try
    {
        FileSystemSecurity security;
        if (File.Exists(FilePath))
        {
            security = File.GetAccessControl(FilePath);
        }
        else
        {
            security = Directory.GetAccessControl(Path.GetDirectoryName(FilePath));
        }
        var rules = security.GetAccessRules(true, true, typeof(NTAccount));

        var currentuser = new WindowsPrincipal(WindowsIdentity.GetCurrent());
        bool result = false;
        foreach (FileSystemAccessRule rule in rules)
        {
            if (0 == (rule.FileSystemRights &
                (FileSystemRights.WriteData | FileSystemRights.Write)))
            {
                continue;
            }

            if (rule.IdentityReference.Value.StartsWith("S-1-"))
            {
                var sid = new SecurityIdentifier(rule.IdentityReference.Value);
                if (!currentuser.IsInRole(sid))
                {
                    continue;
                }
            }
            else
            {
                if (!currentuser.IsInRole(rule.IdentityReference.Value))
                {
                    continue;
                }
            }

            if (rule.AccessControlType == AccessControlType.Deny)
                return false;
            if (rule.AccessControlType == AccessControlType.Allow)
                result = true;
        }
        return result;
    }
    catch
    {
        return false;
    }
}

Answer 5

IMO，您需要像往常一样使用此类目录，但不要在使用前检查权限，而是提供正确的方法来处理 UnauthorizedAccessException 并做出相应的反应。 这种方法更容易，也更不容易出错。

Answer 6

尝试使用我刚刚制作的这个 C# 片段：

using System;
using System.IO;
using System.Security.AccessControl;
using System.Security.Principal;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            string directory = @"C:\downloads";

            DirectoryInfo di = new DirectoryInfo(directory);

            DirectorySecurity ds = di.GetAccessControl();

            foreach (AccessRule rule in ds.GetAccessRules(true, true, typeof(NTAccount)))
            {
                Console.WriteLine("Identity = {0}; Access = {1}", 
                              rule.IdentityReference.Value, rule.AccessControlType);
            }
        }
    }
}

这是您也可以查看的参考。 我的代码可能会让您了解如何在尝试写入目录之前检查权限。

Answer 7

根据此链接： http : //www.authorcode.com/how-to-check-file-permission-to-write-in-c/

使用现有的 SecurityManager 类更容易

string FileLocation = @"C:\test.txt";
FileIOPermission writePermission = new FileIOPermission(FileIOPermissionAccess.Write, FileLocation);
if (SecurityManager.IsGranted(writePermission))
{
  // you have permission
}
else
{
 // permission is required!
}

不过好像已经过时了，建议改用PermissionSet。

[Obsolete("IsGranted is obsolete and will be removed in a future release of the .NET Framework.  Please use the PermissionSet property of either AppDomain or Assembly instead.")]

Answer 8

由于当前版本的 .Net core/Standard 似乎缺少静态方法“GetAccessControl”，因此我不得不修改 @Bryce Wagner 的答案（我继续使用更现代的语法）：

public static class PermissionHelper
{
  public static bool? CurrentUserHasWritePermission(string filePath)

     => new WindowsPrincipal(WindowsIdentity.GetCurrent())
        .SelectWritePermissions(filePath)
        .FirstOrDefault();


  private static IEnumerable<bool?> SelectWritePermissions(this WindowsPrincipal user, string filePath)
     => from rule in filePath
                    .GetFileSystemSecurity()
                    .GetAccessRules(true, true, typeof(NTAccount))
                    .Cast<FileSystemAccessRule>()
        let right = user.HasRightSafe(rule)
        where right.HasValue
        // Deny takes precedence over allow
        orderby right.Value == false descending
        select right;


  private static bool? HasRightSafe(this WindowsPrincipal user, FileSystemAccessRule rule)
  {
     try
     {
        return user.HasRight(rule);
     }
     catch
     {
        return null;
     }
  }

  private static bool? HasRight(this WindowsPrincipal user,FileSystemAccessRule rule )
     => rule switch
     {
        { FileSystemRights: FileSystemRights fileSystemRights } when (fileSystemRights &
                                                                      (FileSystemRights.WriteData | FileSystemRights.Write)) == 0 => null,
        { IdentityReference: { Value: string value } } when value.StartsWith("S-1-") &&
                                                            !user.IsInRole(new SecurityIdentifier(rule.IdentityReference.Value)) => null,
        { IdentityReference: { Value: string value } } when value.StartsWith("S-1-") == false &&
                                                            !user.IsInRole(rule.IdentityReference.Value) => null,
        { AccessControlType: AccessControlType.Deny } => false,
        { AccessControlType: AccessControlType.Allow } => true,
        _ => null
     };


  private static FileSystemSecurity GetFileSystemSecurity(this string filePath)
    => new FileInfo(filePath) switch
    {
       { Exists: true } fileInfo => fileInfo.GetAccessControl(),
       { Exists: false } fileInfo => (FileSystemSecurity)fileInfo.Directory.GetAccessControl(),
       _ => throw new Exception($"Check the file path, {filePath}: something's wrong with it.")
    };
}

Answer 9

private static void GrantAccess(string file)
        {
            bool exists = System.IO.Directory.Exists(file);
            if (!exists)
            {
                DirectoryInfo di = System.IO.Directory.CreateDirectory(file);
                Console.WriteLine("The Folder is created Sucessfully");
            }
            else
            {
                Console.WriteLine("The Folder already exists");
            }
            DirectoryInfo dInfo = new DirectoryInfo(file);
            DirectorySecurity dSecurity = dInfo.GetAccessControl();
            dSecurity.AddAccessRule(new FileSystemAccessRule(new SecurityIdentifier(WellKnownSidType.WorldSid, null), FileSystemRights.FullControl, InheritanceFlags.ObjectInherit | InheritanceFlags.ContainerInherit, PropagationFlags.NoPropagateInherit, AccessControlType.Allow));
            dInfo.SetAccessControl(dSecurity);

        }