Support TLS Resume with client certificates on Linux

src/libraries/Common/src/Interop/Unix/System.Security.Cryptography.Native/Interop.OpenSsl.cs

@@ -24,7 +24,42 @@ internal static partial class OpenSsl
         private const string TlsCacheSizeCtxName = "System.Net.Security.TlsCacheSize";
         private const string TlsCacheSizeEnvironmentVariable = "DOTNET_SYSTEM_NET_SECURITY_TLSCACHESIZE";
         private const SslProtocols FakeAlpnSslProtocol = (SslProtocols)1;   // used to distinguish server sessions with ALPN
-        private static readonly ConcurrentDictionary<SslProtocols, SafeSslContextHandle> s_clientSslContexts = new ConcurrentDictionary<SslProtocols, SafeSslContextHandle>();
+
+        private sealed class SafeSslContextCache : SafeHandleCache<SslContextCacheKey, SafeSslContextHandle> { }
+
+        private static readonly SafeSslContextCache s_clientSslContexts = new();
+
+        internal readonly struct SslContextCacheKey : IEquatable<SslContextCacheKey>
+        {
+            public readonly byte[]? CertificateThumbprint;
+            public readonly SslProtocols SslProtocols;
+
+            public SslContextCacheKey(SslProtocols sslProtocols, byte[]? certificateThumbprint)
+            {
+                SslProtocols = sslProtocols;
+                CertificateThumbprint = certificateThumbprint;
+            }
+
+            public override bool Equals(object? obj) => obj is SslContextCacheKey key && Equals(key);
+
+            public bool Equals(SslContextCacheKey other) =>
+                SslProtocols == other.SslProtocols &&
+                (CertificateThumbprint == null && other.CertificateThumbprint == null ||
+                 CertificateThumbprint != null && other.CertificateThumbprint != null && CertificateThumbprint.AsSpan().SequenceEqual(other.CertificateThumbprint));
+
+            public override int GetHashCode()
+            {
+                HashCode hash = default;
+
+                hash.Add(SslProtocols);
+                if (CertificateThumbprint != null)
+                {
+                    hash.AddBytes(CertificateThumbprint);
+                }
+
+                return hash.ToHashCode();
+            }
+        }
 
         #region internal methods
         internal static SafeChannelBindingHandle? QueryChannelBinding(SafeSslHandle context, ChannelBindingKind bindingType)
@@ -113,6 +148,54 @@ private static SslProtocols CalculateEffectiveProtocols(SslAuthenticationOptions
             return protocols;
         }
 
+        internal static SafeSslContextHandle GetOrCreateSslContextHandle(SslAuthenticationOptions sslAuthenticationOptions, bool allowCached)
+        {
+            SslProtocols protocols = CalculateEffectiveProtocols(sslAuthenticationOptions);
+
+            if (!allowCached)
+            {
+                return AllocateSslContext(sslAuthenticationOptions, protocols, allowCached);
+            }
+
+            if (sslAuthenticationOptions.IsClient)
+            {
+                var key = new SslContextCacheKey(protocols, sslAuthenticationOptions.CertificateContext?.TargetCertificate.GetCertHash(HashAlgorithmName.SHA256));
+
+                return s_clientSslContexts.GetOrCreate(key, static (args) =>
+                {
+                    var (sslAuthOptions, protocols, allowCached) = args;
+                    return AllocateSslContext(sslAuthOptions, protocols, allowCached);
+                }, (sslAuthenticationOptions, protocols, allowCached));
+            }
+
+            // cache in SslStreamCertificateContext is bounded and there is no eviction
+            // so the handle should always be valid,
+
+            bool hasAlpn = sslAuthenticationOptions.ApplicationProtocols != null && sslAuthenticationOptions.ApplicationProtocols.Count != 0;
+
+            SafeSslContextHandle? handle = AllocateSslContext(sslAuthenticationOptions, protocols, allowCached);
+
+            if (!sslAuthenticationOptions.CertificateContext!.SslContexts!.TryGetValue(protocols | (hasAlpn ? FakeAlpnSslProtocol : SslProtocols.None), out handle))
+            {
+                // not found in cache, create and insert
+                handle = AllocateSslContext(sslAuthenticationOptions, protocols, allowCached);
+
+                SafeSslContextHandle cached = sslAuthenticationOptions.CertificateContext!.SslContexts!.GetOrAdd(protocols | (hasAlpn ? FakeAlpnSslProtocol : SslProtocols.None), handle);
+
+                if (handle != cached)
+                {
+                    // lost the race, another thread created the SSL_CTX meanwhile, prefer the cached one
+                    handle.Dispose();
+                    Debug.Assert(handle.IsClosed);
+                    handle = cached;
+                }
+            }
+
+            Debug.Assert(!handle.IsClosed);
+            handle.TryAddRentCount();
+            return handle;
+        }
+
         // This essentially wraps SSL_CTX* aka SSL_CTX_new + setting
         internal static unsafe SafeSslContextHandle AllocateSslContext(SslAuthenticationOptions sslAuthenticationOptions, SslProtocols protocols, bool enableResume)
         {
@@ -188,7 +271,7 @@ internal static unsafe SafeSslContextHandle AllocateSslContext(SslAuthentication
                     Interop.Ssl.SslCtxSetAlpnSelectCb(sslCtx, &AlpnServerSelectCallback, IntPtr.Zero);
                 }
 
-                if (sslAuthenticationOptions.CertificateContext != null)
+                if (sslAuthenticationOptions.CertificateContext != null && sslAuthenticationOptions.IsServer)
                 {
                     SetSslCertificate(sslCtx, sslAuthenticationOptions.CertificateContext.CertificateHandle, sslAuthenticationOptions.CertificateContext.KeyHandle);
 
@@ -257,10 +340,6 @@ internal static void UpdateClientCertificate(SafeSslHandle ssl, SslAuthenticatio
         internal static SafeSslHandle AllocateSslHandle(SslAuthenticationOptions sslAuthenticationOptions)
         {
             SafeSslHandle? sslHandle = null;
-            SafeSslContextHandle? sslCtxHandle = null;
-            SafeSslContextHandle? newCtxHandle = null;
-            SslProtocols protocols = CalculateEffectiveProtocols(sslAuthenticationOptions);
-            bool hasAlpn = sslAuthenticationOptions.ApplicationProtocols != null && sslAuthenticationOptions.ApplicationProtocols.Count != 0;
             bool cacheSslContext = sslAuthenticationOptions.AllowTlsResume && !SslStream.DisableTlsResume && sslAuthenticationOptions.EncryptionPolicy == EncryptionPolicy.RequireEncryption && sslAuthenticationOptions.CipherSuitesPolicy == null;
 
             if (cacheSslContext)
@@ -269,13 +348,12 @@ internal static SafeSslHandle AllocateSslHandle(SslAuthenticationOptions sslAuth
                 {
                     // We don't support client resume on old OpenSSL versions.
                     // We don't want to try on empty TargetName since that is our key.
-                    // And we don't want to mess up with client authentication. It may be possible
-                    // but it seems safe to get full new session.
+                    // If we already have CertificateContext, then we know which cert the user wants to use and we can cache.
+                    // The only client auth scenario where we can't cache is when user provides a cert callback and we don't know
+                    // beforehand which cert will be used. and wan't to avoid resuming session created with different certificate.
                     if (!Interop.Ssl.Capabilities.Tls13Supported ||
                        string.IsNullOrEmpty(sslAuthenticationOptions.TargetHost) ||
-                       sslAuthenticationOptions.CertificateContext != null ||
-                       sslAuthenticationOptions.ClientCertificates?.Count > 0 ||
-                       sslAuthenticationOptions.CertSelectionDelegate != null)
+                       (sslAuthenticationOptions.CertificateContext == null && sslAuthenticationOptions.CertSelectionDelegate != null))
                     {
                         cacheSslContext = false;
                     }
@@ -292,35 +370,14 @@ internal static SafeSslHandle AllocateSslHandle(SslAuthenticationOptions sslAuth
                 }
             }
 
-            if (cacheSslContext)
-            {
-                if (sslAuthenticationOptions.IsServer)
-                {
-                    sslAuthenticationOptions.CertificateContext!.SslContexts!.TryGetValue(protocols | (hasAlpn ? FakeAlpnSslProtocol : SslProtocols.None), out sslCtxHandle);
-                }
-                else
-                {
-
-                    s_clientSslContexts.TryGetValue(protocols, out sslCtxHandle);
-                }
-            }
-
-            if (sslCtxHandle == null)
-            {
-                // We did not get SslContext from cache
-                sslCtxHandle = newCtxHandle = AllocateSslContext(sslAuthenticationOptions, protocols, cacheSslContext);
-
-                if (cacheSslContext)
-                {
-                    bool added = sslAuthenticationOptions.IsServer ?
-                                    sslAuthenticationOptions.CertificateContext!.SslContexts!.TryAdd(protocols | (SslProtocols)(hasAlpn ? 1 : 0), newCtxHandle) :
-                                    s_clientSslContexts.TryAdd(protocols, newCtxHandle);
-                    if (added)
-                    {
-                        newCtxHandle = null;
-                    }
-                }
-            }
+            // We do not touch the SSL_CTX after we create and configure SSL
+            // objects, and SSL object created later in this function will keep an
+            // outstanding up-ref on SSL_CTX.
+            //
+            // For uncached SafeSslContextHandles, the handle will be disposed and closed.
+            // Cached SafeSslContextHandles are returned with increaset rent count so that
+            // Dispose() here will not close the handle.
+            using SafeSslContextHandle sslCtxHandle = GetOrCreateSslContextHandle(sslAuthenticationOptions, cacheSslContext);
 
             GCHandle alpnHandle = default;
             try
@@ -361,19 +418,25 @@ internal static SafeSslHandle AllocateSslHandle(SslAuthenticationOptions sslAuth
                             Crypto.ErrClearError();
                         }
 
-
                         if (cacheSslContext)
                         {
                             sslCtxHandle.TrySetSession(sslHandle, sslAuthenticationOptions.TargetHost);
-                            bool ignored = false;
-                            sslCtxHandle.DangerousAddRef(ref ignored);
+
+                            // Maintain additional rent count for the context so
+                            // that it is not evicted from the cache and future
+                            // SSL objects can reuse it. This call should always
+                            // succeed because already have increased rent count
+                            // when getting the context from the cache
+                            bool success = sslCtxHandle.TryAddRentCount();
+                            Debug.Assert(success);
                             sslHandle.SslContextHandle = sslCtxHandle;
                         }
                     }
 
                     // relevant to TLS 1.3 only: if user supplied a client cert or cert callback,
                     // advertise that we are willing to send the certificate post-handshake.
-                    if (sslAuthenticationOptions.ClientCertificates?.Count > 0 ||
+                    if (sslAuthenticationOptions.CertificateContext != null ||
+                        sslAuthenticationOptions.ClientCertificates?.Count > 0 ||
                         sslAuthenticationOptions.CertSelectionDelegate != null)
                     {
                         Ssl.SslSetPostHandshakeAuth(sslHandle, 1);
@@ -434,10 +497,6 @@ internal static SafeSslHandle AllocateSslHandle(SslAuthenticationOptions sslAuth
 
                 throw;
             }
-            finally
-            {
-                newCtxHandle?.Dispose();
-            }
 
             return sslHandle;
         }
@@ -708,6 +767,12 @@ private static unsafe int NewSessionCallback(IntPtr ssl, IntPtr session)
             Debug.Assert(ssl != IntPtr.Zero);
             Debug.Assert(session != IntPtr.Zero);
 
+            // remember if the session used a certificate, this information is used after
+            // session resumption, the pointer is not being dereferenced and the refcount
+            // is not going to be manipulated.
+            IntPtr cert = Interop.Ssl.SslGetCertificate(ssl);
+            Interop.Ssl.SslSessionSetData(session, cert);
+
             IntPtr ptr = Ssl.SslGetData(ssl);
             if (ptr != IntPtr.Zero)
             {

src/libraries/Common/src/Interop/Unix/System.Security.Cryptography.Native/Interop.Ssl.cs

@@ -116,6 +116,12 @@ internal static unsafe ReadOnlySpan<byte> SslGetAlpnSelected(SafeSslHandle ssl)
         [LibraryImport(Libraries.CryptoNative, EntryPoint = "CryptoNative_SslGetPeerCertificate")]
         internal static partial IntPtr SslGetPeerCertificate(SafeSslHandle ssl);
 
+        [LibraryImport(Libraries.CryptoNative, EntryPoint = "CryptoNative_SslGetCertificate")]
+        internal static partial IntPtr SslGetCertificate(SafeSslHandle ssl);
+
+        [LibraryImport(Libraries.CryptoNative, EntryPoint = "CryptoNative_SslGetCertificate")]
+        internal static partial IntPtr SslGetCertificate(IntPtr ssl);
+
         [LibraryImport(Libraries.CryptoNative, EntryPoint = "CryptoNative_SslGetPeerCertChain")]
         internal static partial SafeSharedX509StackHandle SslGetPeerCertChain(SafeSslHandle ssl);
 
@@ -129,6 +135,9 @@ internal static unsafe ReadOnlySpan<byte> SslGetAlpnSelected(SafeSslHandle ssl)
         [return: MarshalAs(UnmanagedType.Bool)]
         internal static partial bool SslSessionReused(SafeSslHandle ssl);
 
+        [LibraryImport(Libraries.CryptoNative, EntryPoint = "CryptoNative_SslGetSession")]
+        internal static partial IntPtr SslGetSession(SafeSslHandle ssl);
+
         [LibraryImport(Libraries.CryptoNative, EntryPoint = "CryptoNative_SslGetClientCAList")]
         private static partial SafeSharedX509NameStackHandle SslGetClientCAList_private(SafeSslHandle ssl);
 
@@ -182,6 +191,12 @@ internal static unsafe ReadOnlySpan<byte> SslGetAlpnSelected(SafeSslHandle ssl)
         [LibraryImport(Libraries.CryptoNative, EntryPoint = "CryptoNative_SslSessionSetHostname")]
         internal static partial int SessionSetHostname(IntPtr session, IntPtr name);
 
+        [LibraryImport(Libraries.CryptoNative, EntryPoint = "CryptoNative_SslSessionGetData")]
+        internal static partial IntPtr SslSessionGetData(IntPtr session);
+
+        [LibraryImport(Libraries.CryptoNative, EntryPoint = "CryptoNative_SslSessionSetData")]
+        internal static partial void SslSessionSetData(IntPtr session, IntPtr val);
+
         internal static class Capabilities
         {
             // needs separate type (separate static cctor) to be sure OpenSSL is initialized.
@@ -430,7 +445,9 @@ protected override bool ReleaseHandle()
                 Disconnect();
             }
 
-            SslContextHandle?.DangerousRelease();
+            // drop reference to any SSL_CTX handle, any handle present here is being
+            // rented from (client) SSL_CTX cache.
+            SslContextHandle?.Dispose();
 
             if (AlpnHandle.IsAllocated)
             {

src/libraries/Common/src/Interop/Unix/System.Security.Cryptography.Native/Interop.SslCtx.cs

@@ -2,13 +2,15 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System;
+using System.Net;
 using System.Collections.Generic;
 using System.Collections.ObjectModel;
 using System.Diagnostics;
 using System.Net.Security;
 using System.Runtime.InteropServices;
 using System.Security.Cryptography.X509Certificates;
 using System.Text;
+using System.Threading;
 using Microsoft.Win32.SafeHandles;
 
 internal static partial class Interop
@@ -65,12 +67,17 @@ internal static bool AddExtraChainCertificates(SafeSslContextHandle ctx, ReadOnl
 
 namespace Microsoft.Win32.SafeHandles
 {
-    internal sealed class SafeSslContextHandle : SafeHandle
+    internal sealed class SafeSslContextHandle : SafeHandle, ISafeHandleCachable
     {
         // This is session cache keyed by SNI e.g. TargetHost
         private Dictionary<string, IntPtr>? _sslSessions;
         private GCHandle _gch;
 
+        // SSL_CTX handles are cached, so we need to keep track of the
+        // number of times a handle is being used. Once we decide to dispose the handle,
+        // we set the _rentCount to -1.
+        private volatile int _rentCount;
+
         public SafeSslContextHandle()
             : base(IntPtr.Zero, true)
         {
@@ -86,6 +93,38 @@ public override bool IsInvalid
             get { return handle == IntPtr.Zero; }
         }
 
+        public bool TryAddRentCount()
+        {
+            int oldCount;
+
+            do
+            {
+                oldCount = _rentCount;
+                if (oldCount < 0)
+                {
+                    // The handle is already disposed.
+                    return false;
+                }
+            } while (Interlocked.CompareExchange(ref _rentCount, oldCount + 1, oldCount) != oldCount);
+
+            return true;
+        }
+
+        public bool TryMarkForDispose()
+        {
+            return Interlocked.CompareExchange(ref _rentCount, -1, 0) == 0;
+        }
+
+        protected override void Dispose(bool disposing)
+        {
+            if (Interlocked.Decrement(ref _rentCount) < 0)
+            {
+                // _rentCount is 0 if the handle was never rented (e.g. failure during creation),
+                // and is -1 when evicted from cache.
+                base.Dispose(disposing);
+            }
+        }
+
         protected override bool ReleaseHandle()
         {
             if (_sslSessions != null)