Merge pull request #2889 from stephentoub/home_directory_unix

Fix access to user's home directory on Unix

Author: stephentoub

src/Common/src/Interop/Unix/libc/Interop.getegid.cs renamed to src/Common/src/Interop/Unix/System.Native/Interop.GetEGid.cs

@@ -6,9 +6,9 @@
 
 internal static partial class Interop
 {
-    internal static partial class libc
+    internal static partial class Sys
     {
-        [DllImport(Libraries.Libc)]
-        internal static extern int getegid();
+        [DllImport(Libraries.SystemNative)]
+        internal static extern int GetEGid();
     }
 }

src/Common/src/Interop/Unix/libc/Interop.geteuid.cs renamed to src/Common/src/Interop/Unix/System.Native/Interop.GetEUid.cs

@@ -6,9 +6,9 @@
 
 internal static partial class Interop
 {
-    internal static partial class libc
+    internal static partial class Sys
     {
-        [DllImport(Libraries.Libc)]
-        internal static extern int geteuid();
+        [DllImport(Libraries.SystemNative)]
+        internal static extern int GetEUid();
     }
 }

src/Common/src/Interop/Unix/System.Native/Interop.GetPwUid.cs

@@ -0,0 +1,25 @@
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+using System;
+using System.Runtime.InteropServices;
+
+internal static partial class Interop
+{
+    internal static partial class Sys
+    {
+        internal unsafe struct Passwd
+        {
+            internal byte* Name;
+            internal byte* Password;
+            internal int   UserId;
+            internal int   GroupId;
+            internal byte* UserInfo;
+            internal byte* HomeDirectory;
+            internal byte* Shell;
+        };
+
+        [DllImport(Libraries.SystemNative, SetLastError = true)]
+        internal static extern unsafe int GetPwUid(int uid, out Passwd pwd, byte* buf, long bufLen, out IntPtr result);
+    }
+}

src/Common/src/System/IO/PersistedFiles.Unix.cs

@@ -2,6 +2,7 @@
 // Licensed under the MIT license. See LICENSE file in the project root for full license information.
 
 using System.Diagnostics;
+using System.Runtime.InteropServices;
 
 namespace System.IO
 {
@@ -81,8 +82,7 @@ internal static string GetUserFeatureDirectory(params string[] featurePathParts)
 
         private static void EnsureUserDirectories()
         {
-            // TODO (2820): Use getpwuid_r(geteuid(), ...) instead of the HOME environment variable
-            string userHomeDirectory = Environment.GetEnvironmentVariable("HOME");
+            string userHomeDirectory = GetHomeDirectory();
 
             if (string.IsNullOrEmpty(userHomeDirectory))
             {
@@ -94,5 +94,95 @@ private static void EnsureUserDirectories()
                 TopLevelHiddenDirectory,
                 SecondLevelDirectory);
         }
+
+        /// <summary>Gets the current user's home directory.</summary>
+        /// <returns>The path to the home directory, or null if it could not be determined.</returns>
+        internal static string GetHomeDirectory()
+        {
+            // First try to get the user's home directory from the HOME environment variable.
+            // This should work in most cases.
+            string userHomeDirectory = Environment.GetEnvironmentVariable("HOME");
+            if (!string.IsNullOrEmpty(userHomeDirectory))
+                return userHomeDirectory;
+
+            // In initialization conditions, however, the "HOME" enviroment variable may 
+            // not yet be set. For such cases, consult with the password entry.
+            unsafe
+            {
+                // First try with a buffer that should suffice for 99% of cases.
+                // Note that, theoretically, userHomeDirectory may be null in the success case 
+                // if we simply couldn't find a home directory for the current user.
+                // In that case, we pass back the null value and let the caller decide
+                // what to do.
+                const int BufLen = 1024;
+                byte* stackBuf = stackalloc byte[BufLen];
+                if (TryGetHomeDirectoryFromPasswd(stackBuf, BufLen, out userHomeDirectory))
+                    return userHomeDirectory;
+
+                // Fallback to heap allocations if necessary, growing the buffer until
+                // we succeed.  TryGetHomeDirectory will throw if there's an unexpected error.
+                int lastBufLen = BufLen;
+                while (true)
+                {
+                    lastBufLen *= 2;
+                    byte[] heapBuf = new byte[lastBufLen];
+                    fixed (byte* buf = heapBuf)
+                    {
+                        if (TryGetHomeDirectoryFromPasswd(buf, heapBuf.Length, out userHomeDirectory))
+                            return userHomeDirectory;
+                    }
+                }
+            }
+        }
+
+        /// <summary>Wrapper for getpwuid_r.</summary>
+        /// <param name="buf">The scratch buffer to pass into getpwuid_r.</param>
+        /// <param name="bufLen">The length of <paramref name="buf"/>.</param>
+        /// <param name="path">The resulting path; null if the user didn't have an entry.</param>
+        /// <returns>true if the call was successful (path may still be null); false is a larger buffer is needed.</returns>
+        private static unsafe bool TryGetHomeDirectoryFromPasswd(byte* buf, int bufLen, out string path)
+        {
+            while (true)
+            {
+                // Call getpwuid_r to get the passwd struct
+                Interop.Sys.Passwd passwd;
+                IntPtr result;
+                int rv = Interop.Sys.GetPwUid(Interop.Sys.GetEUid(), out passwd, buf, bufLen, out result);
+
+                // If the call succeeds, give back the home directory path retrieved
+                if (rv == 0)
+                {
+                    if (result == IntPtr.Zero)
+                    {
+                        // Current user's entry could not be found
+                        path = null; // we'll still return true, as false indicates the buffer was too small
+                    }
+                    else
+                    {
+                        Debug.Assert(result == (IntPtr)(&passwd));
+                        Debug.Assert(passwd.HomeDirectory != null);
+                        path = Marshal.PtrToStringAnsi((IntPtr)passwd.HomeDirectory);
+                    }
+                    return true;
+                }
+
+                // If the call failed because it was interrupted, try again.
+                Interop.ErrorInfo errorInfo = Interop.Sys.GetLastErrorInfo();
+                if (errorInfo.Error == Interop.Error.EINTR)
+                    continue;
+
+                // If the call failed because the buffer was too small, return false to 
+                // indicate the caller should try again with a larger buffer.
+                if (errorInfo.Error == Interop.Error.ERANGE)
+                {
+                    path = null;
+                    return false;
+                }
+
+                // Otherwise, fail.
+                throw new IOException(errorInfo.GetErrorMessage(), errorInfo.RawErrno);
+            }
+        }
+
     }
 }

src/Native/System.Native/CMakeLists.txt

@@ -4,6 +4,7 @@ set(NATIVE_SOURCES
     pal_errno.cpp
     pal_exec.cpp
     pal_stat.cpp
+    pal_uid.cpp
 )
 
 add_library(System.Native

src/Native/System.Native/pal_uid.cpp

@@ -0,0 +1,74 @@
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+#include "../config.h"
+#include "pal_uid.h"
+
+#include <assert.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <sys/types.h>
+#include <pwd.h>
+
+/**
+* Gets a password structure for the given uid.
+* Implemented as shim to getpwuid_r(3).
+*
+* Returns 0 for success, -1 for failure. Sets errno on failure.
+*/
+extern "C"
+int32_t GetPwUid(
+	int32_t  uid,
+	Passwd*  pwd,
+	char*    buf,
+	int64_t  buflen,
+	Passwd** result)
+{
+	assert(pwd != nullptr);
+	assert(buf != nullptr);
+	assert(buflen >= 0);
+	assert(result != nullptr);
+
+	struct passwd nativePwd;
+	struct passwd* nativePwdResultPtr;
+	int rv = getpwuid_r(uid, &nativePwd, buf, buflen, &nativePwdResultPtr);
+
+	// If successful, the result will be null if the user couldn't be found,
+	// or it'll contain the address of the provided pwd structure, into
+	// which the results are stored.
+	if (rv == 0 && nativePwdResultPtr != nullptr)
+	{
+		assert(nativePwdResultPtr == &nativePwd);
+		
+		pwd->Name = nativePwd.pw_name;
+		pwd->Password = nativePwd.pw_passwd;
+		pwd->UserId = nativePwd.pw_uid;
+		pwd->GroupId = nativePwd.pw_gid;
+		pwd->UserInfo = nativePwd.pw_gecos;
+		pwd->HomeDirectory = nativePwd.pw_dir;
+		pwd->Shell = nativePwd.pw_shell;
+		*result = pwd;
+	}
+	else
+	{
+		// Make sure we zero out the results fields, as the managed
+		// caller could be using out variables and expect them to be initialized
+		// after the call.
+		*pwd = { };
+		*result = nullptr;
+	}
+
+	return rv;
+}
+
+extern "C"
+int32_t GetEUid()
+{
+	return geteuid();
+}
+
+extern "C"
+int32_t GetEGid()
+{
+	return getegid();
+}

src/Native/System.Native/pal_uid.h

@@ -0,0 +1,51 @@
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+#pragma once
+
+#include <stdint.h>
+
+/**
+* Passwd struct 
+*/
+struct Passwd {
+	char*   Name;
+	char*   Password; 
+	int32_t UserId;
+	int32_t GroupId;
+	char*   UserInfo;
+	char*   HomeDirectory;
+	char*   Shell;
+};
+
+/**
+* Gets a password structure for the given uid. 
+* Implemented as shim to getpwuid_r(3).
+*
+* Returns 0 for success, -1 for failure. Sets errno on failure.
+*/
+extern "C"
+int32_t GetPwUid(
+	int32_t  uid,
+	Passwd*  pwd,
+	char*    buf,
+	int64_t  buflen,
+	Passwd** result);
+
+/**
+* Gets and returns the effective user's identity.
+* Implemented as shim to geteuid(2).
+*
+* Always succeeds.
+*/
+extern "C"
+int32_t GetEUid();
+
+/**
+* Gets and returns the effective group's identity.
+* Implemented as shim to getegid(2).
+*
+* Always succeeds.
+*/
+extern "C"
+int32_t GetEGid();

src/System.Console/src/Resources/Strings.resx

@@ -198,4 +198,7 @@
   <data name="PlatformNotSupported_GettingColor" xml:space="preserve">
     <value>This platform does not support getting the current color.</value>
   </data>
+  <data name="PersistedFiles_NoHomeDirectory" xml:space="preserve">
+    <value>The home directory of the current user could not be determined.</value>
+  </data>
 </root>

src/System.Console/src/System.Console.csproj

@@ -96,6 +96,12 @@
     <Compile Include="$(CommonPath)\Microsoft\Win32\SafeHandles\SafeFileHandle.Unix.cs">
       <Link>Common\Microsoft\Win32\SafeHandles\SafeFileHandle.Unix.cs</Link>
     </Compile>
+    <Compile Include="$(CommonPath)\System\IO\PersistedFiles.Unix.cs">
+      <Link>Common\System\IO\PersistedFiles.Unix.cs</Link>
+    </Compile>
+    <Compile Include="$(CommonPath)\System\IO\PersistedFiles.Names.Unix.cs">
+      <Link>Common\System\IO\PersistedFiles.Names.Unix.cs</Link>
+    </Compile>
     <Compile Include="$(CommonPath)\System\IO\StringBuilderCache.cs">
       <Link>Common\System\IO\StringBuilderCache.cs</Link>
     </Compile>
@@ -132,6 +138,12 @@
     <Compile Include="$(CommonPath)\Interop\Unix\libc\Interop.snprintf.cs">
       <Link>Common\Interop\Unix\Interop.snprintf.cs</Link>
     </Compile>
+    <Compile Include="$(CommonPath)\Interop\Unix\System.Native\Interop.GetEUid.cs">
+      <Link>Common\Interop\Unix\Interop.GetEUid.cs</Link>
+    </Compile>
+    <Compile Include="$(CommonPath)\Interop\Unix\System.Native\Interop.GetPwUid.cs">
+      <Link>Common\Interop\Unix\Interop.GetPwUid.cs</Link>
+    </Compile>
     <Compile Include="$(CommonPath)\Interop\Unix\System.Native\Interop.Stat.cs">
       <Link>Common\Interop\Unix\Interop.Stat.cs</Link>
     </Compile>

src/System.Console/src/System/ConsolePal.Unix.cs

@@ -490,7 +490,7 @@ private static Database ReadDatabase(string term)
                     }
 
                     // Then try in the user's home directory.
-                    string home = Environment.GetEnvironmentVariable("HOME");
+                    string home = PersistedFiles.GetHomeDirectory();
                     if (!string.IsNullOrWhiteSpace(home) && (db = ReadDatabase(term, home + "/.terminfo")) != null)
                     {
                         return db;