.NET SslStream doesn't close TLS connection properly

问题:

.NET's SslStream class does not send the close_notify alert before closing the connection.

How can I send the close_notify alert manually?

回答1:

Thanks for this question. It pointed me into the right direction, that there is a bug in .Net, which I do not very often think about.

I bumped into this problem during writing of my implementation of FTPS server and Filezilla (or GnuTLS probably) client was complaining "GnuTLS error -110 in gnutls_record_recv: The TLS connection was non-properly terminated". I think it is a quite significant drawback in SslStream implementation.

So I ended up with writing a wrapper which sends this alert before closing the stream:

public class FixedSslStream : SslStream {     public FixedSslStream(Stream innerStream)         : base(innerStream) {     }     public FixedSslStream(Stream innerStream, bool leaveInnerStreamOpen)         : base(innerStream, leaveInnerStreamOpen) {     }     public FixedSslStream(Stream innerStream, bool leaveInnerStreamOpen, RemoteCertificateValidationCallback userCertificateValidationCallback)         : base(innerStream, leaveInnerStreamOpen, userCertificateValidationCallback) {     }     public FixedSslStream(Stream innerStream, bool leaveInnerStreamOpen, RemoteCertificateValidationCallback userCertificateValidationCallback, LocalCertificateSelectionCallback userCertificateSelectionCallback)         : base(innerStream, leaveInnerStreamOpen, userCertificateValidationCallback, userCertificateSelectionCallback) {     }     public FixedSslStream(Stream innerStream, bool leaveInnerStreamOpen, RemoteCertificateValidationCallback userCertificateValidationCallback, LocalCertificateSelectionCallback userCertificateSelectionCallback, EncryptionPolicy encryptionPolicy)         : base(innerStream, leaveInnerStreamOpen, userCertificateValidationCallback, userCertificateSelectionCallback, encryptionPolicy) {     }     public override void Close() {         try {             SslDirectCall.CloseNotify(this);         } finally {             base.Close();         }     } } 

And the following code is to make it working (this code requires assembly to be 'unsafe'):

public unsafe static class SslDirectCall {     public static void CloseNotify(SslStream sslStream) {         if (sslStream.IsAuthenticated) {             bool isServer = sslStream.IsServer;              byte[] result;             int resultSz;             var asmbSystem = typeof(System.Net.Authorization).Assembly;              int SCHANNEL_SHUTDOWN = 1;             var workArray = BitConverter.GetBytes(SCHANNEL_SHUTDOWN);              var sslstate = ReflectUtil.GetField(sslStream, "_SslState");             var context = ReflectUtil.GetProperty(sslstate, "Context");              var securityContext = ReflectUtil.GetField(context, "m_SecurityContext");             var securityContextHandleOriginal = ReflectUtil.GetField(securityContext, "_handle");             NativeApi.SSPIHandle securityContextHandle = default(NativeApi.SSPIHandle);             securityContextHandle.HandleHi = (IntPtr)ReflectUtil.GetField(securityContextHandleOriginal, "HandleHi");             securityContextHandle.HandleLo = (IntPtr)ReflectUtil.GetField(securityContextHandleOriginal, "HandleLo");              var credentialsHandle = ReflectUtil.GetField(context, "m_CredentialsHandle");             var credentialsHandleHandleOriginal = ReflectUtil.GetField(credentialsHandle, "_handle");             NativeApi.SSPIHandle credentialsHandleHandle = default(NativeApi.SSPIHandle);             credentialsHandleHandle.HandleHi = (IntPtr)ReflectUtil.GetField(credentialsHandleHandleOriginal, "HandleHi");             credentialsHandleHandle.HandleLo = (IntPtr)ReflectUtil.GetField(credentialsHandleHandleOriginal, "HandleLo");              int bufferSize = 1;             NativeApi.SecurityBufferDescriptor securityBufferDescriptor = new NativeApi.SecurityBufferDescriptor(bufferSize);             NativeApi.SecurityBufferStruct[] unmanagedBuffer = new NativeApi.SecurityBufferStruct[bufferSize];              fixed (NativeApi.SecurityBufferStruct* ptr = unmanagedBuffer)             fixed (void* workArrayPtr = workArray) {                 securityBufferDescriptor.UnmanagedPointer = (void*)ptr;                  unmanagedBuffer[0].token = (IntPtr)workArrayPtr;                 unmanagedBuffer[0].count = workArray.Length;                 unmanagedBuffer[0].type = NativeApi.BufferType.Token;                  NativeApi.SecurityStatus status;                 status = (NativeApi.SecurityStatus)NativeApi.ApplyControlToken(ref securityContextHandle, securityBufferDescriptor);                 if (status == NativeApi.SecurityStatus.OK) {                     unmanagedBuffer[0].token = IntPtr.Zero;                     unmanagedBuffer[0].count = 0;                     unmanagedBuffer[0].type = NativeApi.BufferType.Token;                      NativeApi.SSPIHandle contextHandleOut = default(NativeApi.SSPIHandle);                     NativeApi.ContextFlags outflags = NativeApi.ContextFlags.Zero;                     long ts = 0;                      var inflags = NativeApi.ContextFlags.SequenceDetect |                                 NativeApi.ContextFlags.ReplayDetect |                                 NativeApi.ContextFlags.Confidentiality |                                 NativeApi.ContextFlags.AcceptExtendedError |                                 NativeApi.ContextFlags.AllocateMemory |                                 NativeApi.ContextFlags.InitStream;                      if (isServer) {                         status = (NativeApi.SecurityStatus)NativeApi.AcceptSecurityContext(ref credentialsHandleHandle, ref securityContextHandle, null,                             inflags, NativeApi.Endianness.Native, ref contextHandleOut, securityBufferDescriptor, ref outflags, out ts);                     } else {                         status = (NativeApi.SecurityStatus)NativeApi.InitializeSecurityContextW(ref credentialsHandleHandle, ref securityContextHandle, null,                             inflags, 0, NativeApi.Endianness.Native, null, 0, ref contextHandleOut, securityBufferDescriptor, ref outflags, out ts);                     }                     if (status == NativeApi.SecurityStatus.OK) {                         byte[] resultArr = new byte[unmanagedBuffer[0].count];                         Marshal.Copy(unmanagedBuffer[0].token, resultArr, 0, resultArr.Length);                         Marshal.FreeCoTaskMem(unmanagedBuffer[0].token);                         result = resultArr;                         resultSz = resultArr.Length;                     } else {                         throw new InvalidOperationException(string.Format("AcceptSecurityContext/InitializeSecurityContextW returned [{0}] during CloseNotify.", status));                     }                 } else {                     throw new InvalidOperationException(string.Format("ApplyControlToken returned [{0}] during CloseNotify.", status));                 }             }              var innerStream = (Stream)ReflectUtil.GetProperty(sslstate, "InnerStream");             innerStream.Write(result, 0, resultSz);         }     } } 

Windows API used:

public unsafe static class NativeApi {     internal enum BufferType {         Empty,         Data,         Token,         Parameters,         Missing,         Extra,         Trailer,         Header,         Padding = 9,         Stream,         ChannelBindings = 14,         TargetHost = 16,         ReadOnlyFlag = -2147483648,         ReadOnlyWithChecksum = 268435456     }      [StructLayout(LayoutKind.Sequential, Pack = 1)]     internal struct SSPIHandle {         public IntPtr HandleHi;         public IntPtr HandleLo;         public bool IsZero {             get {                 return this.HandleHi == IntPtr.Zero && this.HandleLo == IntPtr.Zero;             }         }         [ReliabilityContract(Consistency.WillNotCorruptState, Cer.Success)]         internal void SetToInvalid() {             this.HandleHi = IntPtr.Zero;             this.HandleLo = IntPtr.Zero;         }         public override string ToString() {             return this.HandleHi.ToString("x") + ":" + this.HandleLo.ToString("x");         }     }     [StructLayout(LayoutKind.Sequential)]     internal class SecurityBufferDescriptor {         public readonly int Version;         public readonly int Count;         public unsafe void* UnmanagedPointer;         public SecurityBufferDescriptor(int count) {             this.Version = 0;             this.Count = count;             this.UnmanagedPointer = null;         }     }      [StructLayout(LayoutKind.Sequential)]     internal struct SecurityBufferStruct {         public int count;         public BufferType type;         public IntPtr token;         public static readonly int Size = sizeof(SecurityBufferStruct);     }      internal enum SecurityStatus {         OK,         ContinueNeeded = 590610,         CompleteNeeded,         CompAndContinue,         ContextExpired = 590615,         CredentialsNeeded = 590624,         Renegotiate,         OutOfMemory = -2146893056,         InvalidHandle,         Unsupported,         TargetUnknown,         InternalError,         PackageNotFound,         NotOwner,         CannotInstall,         InvalidToken,         CannotPack,         QopNotSupported,         NoImpersonation,         LogonDenied,         UnknownCredentials,         NoCredentials,         MessageAltered,         OutOfSequence,         NoAuthenticatingAuthority,         IncompleteMessage = -2146893032,         IncompleteCredentials = -2146893024,         BufferNotEnough,         WrongPrincipal,         TimeSkew = -2146893020,         UntrustedRoot,         IllegalMessage,         CertUnknown,         CertExpired,         AlgorithmMismatch = -2146893007,         SecurityQosFailed,         SmartcardLogonRequired = -2146892994,         UnsupportedPreauth = -2146892989,         BadBinding = -2146892986     }     [Flags]     internal enum ContextFlags {         Zero = 0,         Delegate = 1,         MutualAuth = 2,         ReplayDetect = 4,         SequenceDetect = 8,         Confidentiality = 16,         UseSessionKey = 32,         AllocateMemory = 256,         Connection = 2048,         InitExtendedError = 16384,         AcceptExtendedError = 32768,         InitStream = 32768,         AcceptStream = 65536,         InitIntegrity = 65536,         AcceptIntegrity = 131072,         InitManualCredValidation = 524288,         InitUseSuppliedCreds = 128,         InitIdentify = 131072,         AcceptIdentify = 524288,         ProxyBindings = 67108864,         AllowMissingBindings = 268435456,         UnverifiedTargetName = 536870912     }     internal enum Endianness {         Network,         Native = 16     }      [ReliabilityContract(Consistency.WillNotCorruptState, Cer.MayFail)]     [DllImport("secur32.dll", ExactSpelling = true, SetLastError = true)]     internal static extern int ApplyControlToken(ref SSPIHandle contextHandle, [In] [Out] SecurityBufferDescriptor outputBuffer);      [ReliabilityContract(Consistency.WillNotCorruptState, Cer.MayFail)]     [DllImport("secur32.dll", ExactSpelling = true, SetLastError = true)]     internal unsafe static extern int AcceptSecurityContext(ref SSPIHandle credentialHandle, ref SSPIHandle contextHandle, [In] SecurityBufferDescriptor inputBuffer, [In] ContextFlags inFlags, [In] Endianness endianness, ref SSPIHandle outContextPtr, [In] [Out] SecurityBufferDescriptor outputBuffer, [In] [Out] ref ContextFlags attributes, out long timeStamp);      [ReliabilityContract(Consistency.WillNotCorruptState, Cer.MayFail)]     [DllImport("secur32.dll", ExactSpelling = true, SetLastError = true)]     internal unsafe static extern int InitializeSecurityContextW(ref SSPIHandle credentialHandle, ref SSPIHandle contextHandle, [In] byte* targetName, [In] ContextFlags inFlags, [In] int reservedI, [In] Endianness endianness, [In] SecurityBufferDescriptor inputBuffer, [In] int reservedII, ref SSPIHandle outContextPtr, [In] [Out] SecurityBufferDescriptor outputBuffer, [In] [Out] ref ContextFlags attributes, out long timeStamp); } 

Reflection utilities:

public static class ReflectUtil {     public static object GetField(object obj, string fieldName) {         var tp = obj.GetType();         var info = GetAllFields(tp)             .Where(f => f.Name == fieldName).Single();         return info.GetValue(obj);     }     public static void SetField(object obj, string fieldName, object value) {         var tp = obj.GetType();         var info = GetAllFields(tp)             .Where(f => f.Name == fieldName).Single();         info.SetValue(obj, value);     }     public static object GetStaticField(Assembly assembly, string typeName, string fieldName) {         var tp = assembly.GetType(typeName);         var info = GetAllFields(tp)             .Where(f => f.IsStatic)             .Where(f => f.Name == fieldName).Single();         return info.GetValue(null);     }      public static object GetProperty(object obj, string propertyName) {         var tp = obj.GetType();         var info = GetAllProperties(tp)             .Where(f => f.Name == propertyName).Single();         return info.GetValue(obj, null);     }     public static object CallMethod(object obj, string methodName, params object[] prm) {         var tp = obj.GetType();         var info = GetAllMethods(tp)             .Where(f => f.Name == methodName && f.GetParameters().Length == prm.Length).Single();         object rez = info.Invoke(obj, prm);         return rez;     }     public static object NewInstance(Assembly assembly, string typeName, params object[] prm) {         var tp = assembly.GetType(typeName);         var info = tp.GetConstructors()             .Where(f => f.GetParameters().Length == prm.Length).Single();         object rez = info.Invoke(prm);         return rez;     }     public static object InvokeStaticMethod(Assembly assembly, string typeName, string methodName, params object[] prm) {         var tp = assembly.GetType(typeName);         var info = GetAllMethods(tp)             .Where(f => f.IsStatic)             .Where(f => f.Name == methodName && f.GetParameters().Length == prm.Length).Single();         object rez = info.Invoke(null, prm);         return rez;     }     public static object GetEnumValue(Assembly assembly, string typeName, int value) {         var tp = assembly.GetType(typeName);         object rez = Enum.ToObject(tp, value);         return rez;     }      private static IEnumerable<FieldInfo> GetAllFields(Type t) {         if (t == null)             return Enumerable.Empty<FieldInfo>();          BindingFlags flags = BindingFlags.Public | BindingFlags.NonPublic |                              BindingFlags.Static | BindingFlags.Instance |                              BindingFlags.DeclaredOnly;         return t.GetFields(flags).Concat(GetAllFields(t.BaseType));     }     private static IEnumerable<PropertyInfo> GetAllProperties(Type t) {         if (t == null)             return Enumerable.Empty<PropertyInfo>();          BindingFlags flags = BindingFlags.Public | BindingFlags.NonPublic |                              BindingFlags.Static | BindingFlags.Instance |                              BindingFlags.DeclaredOnly;         return t.GetProperties(flags).Concat(GetAllProperties(t.BaseType));     }     private static IEnumerable<MethodInfo> GetAllMethods(Type t) {         if (t == null)             return Enumerable.Empty<MethodInfo>();          BindingFlags flags = BindingFlags.Public | BindingFlags.NonPublic |                              BindingFlags.Static | BindingFlags.Instance |                              BindingFlags.DeclaredOnly;         return t.GetMethods(flags).Concat(GetAllMethods(t.BaseType));     } } 

I am not experienced in writing reliable interaction with unmanaged environment, so I hope somebody can have a look and fix issues (and maybe make it 'safe').

回答2:

It's a bug in .NET's usage of the underlying security API. Note another question by me about being unable to select a specific cypher suite - they really botched up this API wrapper...

回答3:

For the record, SslStream at least in .NET 2.0 also doesn't appear to response to a close_notify from the other side. This means that calling OpenSSL's SSL_Shutdown() properly, i.e. twice - once to initiate the shutdown and again to wait for the response - will hang on the second call.

文章来源: .NET SslStream doesn't close TLS connection properly