Fix resolving global symbols when LoadLibrary() is called after dlopen()

Usage of first_automatic_object cache is wrong. This cache is filled by all
loaded DLL files (either implicitly or explicitly with LoadLibrary() call)
by EnumProcessModules() call at first usage of dlopen(). So dlsym() can
resolve global symbols only if they were loaded prior to dlopen() call. Any
future usage of LoadLibrary() does not include newly loaded DLLs into
first_automatic_object cache.

To fix this problem, first_automatic_object cache is fully removed and
EnumProcessModules() call is issued directly in dlsym() call.

As EnumProcessModules() returns all DLLs, included those which were loaded
by dlopen() with RTLD_LOCAL, it may break RTLD_LOCAL support. To address
this problem switch linked-list of all loaded DLLs with RTLD_GLOBAL to
linked-list of all loaded DLLs with RTLD_LOCAL flag. And then skip modules
from EnumProcessModules() which are in linked-list.

Also in WinAPI all DLLs loaded by LoadLibrary() behaves like RTLD_GLOBAL.
So above change is compatible with this behavior.

There may be another problem. Before retrieving HMODULE for DLL filename
(which is done by LoadLibrary()), it is not possible to detect if DLL was
already loaded by RTLD_LOCAL or not. And after calling LoadLibrary() it is
not possible to know if DLL was loaded either by dlsym() with RTLD_LOCAL or
by LoadLibrary() (which is equivalent to RTLD_GLOBAL). To address this
problem, compare number of loaded modules (counted by EnumProcessModules())
before and after LoadLibrary() called from dlsym(). If number does not
change it means that DLL was already loaded. So based on this result either
add or remove HMODULE from linked-list of RTLD_LOCAL modules.

Added test demonstrate usage of:

global = dlopen(NULL, RTLD_GLOBAL);   /* global handle */
LoadLibrary("library.dll");           /* this provides function */
function = dlsym(global, "function"); /* resolve function from library.dll */

6 files changed, 144 insertions, 112 deletions

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 48945b2..a13cf99 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -63,6 +63,8 @@ if (BUILD_TESTS)
   enable_testing()
   add_library(testdll SHARED testdll.c)
   set_target_properties(testdll PROPERTIES PREFIX "")
+  add_library(testdll3 SHARED testdll3.c)
+  set_target_properties(testdll3 PROPERTIES PREFIX "")
   add_executable(t_dlfcn test.c)
   target_link_libraries(t_dlfcn dl)
   add_test (NAME t_dlfcn COMMAND t_dlfcn)
diff --git a/Makefile b/Makefile
index c02dce0..a0f5cb9 100644
--- a/Makefile
+++ b/Makefile
@@ -66,7 +66,10 @@ test.exe: test.o $(TARGETS)
 testdll.dll: testdll.c

         $(CC) -shared -o $@ $^

 

-test: $(TARGETS) test.exe testdll.dll

+testdll3.dll: testdll3.c

+        $(CC) -shared -o $@ $^

+

+test: $(TARGETS) test.exe testdll.dll testdll3.dll

         $(WINE) test.exe

 

 clean::

@@ -74,7 +77,7 @@ clean::
                 dlfcn.o \

                 libdl.dll libdl.a libdl.def libdl.dll.a libdl.lib libdl.exp \

                 tmptest.c tmptest.dll \

-                test.exe testdll.dll

+                test.exe testdll.dll testdll3.dll

 

 distclean: clean

         rm -f config.mak

diff --git a/cmake-test/CMakeLists.txt b/cmake-test/CMakeLists.txt
index 532f2b8..b853920 100644
--- a/cmake-test/CMakeLists.txt
+++ b/cmake-test/CMakeLists.txt
@@ -8,6 +8,8 @@ find_package(dlfcn-win32 REQUIRED)
 
 add_library(testdll SHARED ../testdll.c)
 set_target_properties(testdll PROPERTIES PREFIX "")
+add_library(testdll3 SHARED ../testdll3.c)
+set_target_properties(testdll3 PROPERTIES PREFIX "")
 add_executable(t_dlfcn ../test.c)
 target_link_libraries(t_dlfcn dlfcn-win32::dl)
 enable_testing()
diff --git a/dlfcn.c b/dlfcn.c
index b356558..1e706f0 100644
--- a/dlfcn.c
+++ b/dlfcn.c
@@ -2,6 +2,7 @@
  * dlfcn-win32

  * Copyright (c) 2007 Ramiro Polla

  * Copyright (c) 2015 Tiancheng "Timothy" Gu

+ * Copyright (c) 2019 Pali Rohár <pali.rohar@gmail.com>

  *

  * dlfcn-win32 is free software; you can redistribute it and/or

  * modify it under the terms of the GNU Lesser General Public

@@ -52,57 +53,48 @@
  * any kind of thread safety.

  */

 

-typedef struct global_object {

+typedef struct local_object {

     HMODULE hModule;

-    struct global_object *previous;

-    struct global_object *next;

-} global_object;

+    struct local_object *previous;

+    struct local_object *next;

+} local_object;

 

-static global_object first_object;

-static global_object first_automatic_object;

-static int auto_ref_count = 0;

+static local_object first_object;

 

-/* These functions implement a double linked list for the global objects. */

-static global_object *global_search( global_object *start, HMODULE hModule )

+/* These functions implement a double linked list for the local objects. */

+static local_object *local_search( HMODULE hModule )

 {

-    global_object *pobject;

+    local_object *pobject;

 

     if( hModule == NULL )

         return NULL;

 

-    for( pobject = start; pobject; pobject = pobject->next )

+    for( pobject = &first_object; pobject; pobject = pobject->next )

         if( pobject->hModule == hModule )

             return pobject;

 

     return NULL;

 }

 

-static void global_add( global_object *start, HMODULE hModule )

+static void local_add( HMODULE hModule )

 {

-    global_object *pobject;

-    global_object *nobject;

+    local_object *pobject;

+    local_object *nobject;

 

     if( hModule == NULL )

         return;

 

-    pobject = global_search( start, hModule );

+    pobject = local_search( hModule );

 

     /* Do not add object again if it's already on the list */

     if( pobject )

         return;

 

-    if( start == &first_automatic_object )

-    {

-        pobject = global_search( &first_object, hModule );

-        if( pobject )

-            return;

-    }

-

-    for( pobject = start; pobject->next; pobject = pobject->next );

+    for( pobject = &first_object; pobject->next; pobject = pobject->next );

 

-    nobject = (global_object*) malloc( sizeof( global_object ) );

+    nobject = (local_object*) malloc( sizeof( local_object ) );

 

-    /* Should this be enough to fail global_add, and therefore also fail

+    /* Should this be enough to fail local_add, and therefore also fail

      * dlopen?

      */

     if( !nobject )

@@ -114,14 +106,14 @@ static void global_add( global_object *start, HMODULE hModule )
     nobject->hModule = hModule;

 }

 

-static void global_rem( global_object *start, HMODULE hModule )

+static void local_rem( HMODULE hModule )

 {

-    global_object *pobject;

+    local_object *pobject;

 

     if( hModule == NULL )

         return;

 

-    pobject = global_search( start, hModule );

+    pobject = local_search( hModule );

 

     if( !pobject )

         return;

@@ -224,10 +216,6 @@ void *dlopen( const char *file, int mode )
 

     if( file == 0 )

     {

-        HMODULE hAddtnlMods[1024]; // Already loaded modules

-        HANDLE hCurrentProc = GetCurrentProcess( );

-        DWORD cbNeeded;

-

         /* POSIX says that if the value of file is 0, a handle on a global

          * symbol object must be provided. That object must be able to access

          * all symbols from the original program file, and any objects loaded

@@ -242,27 +230,13 @@ void *dlopen( const char *file, int mode )
 

         if( !hModule )

             save_err_ptr_str( file );

-

-

-        /* GetModuleHandle( NULL ) only returns the current program file. So

-         * if we want to get ALL loaded module including those in linked DLLs,

-         * we have to use EnumProcessModules( ).

-         */

-        if( EnumProcessModules( hCurrentProc, hAddtnlMods,

-            sizeof( hAddtnlMods ), &cbNeeded ) != 0 )

-        {

-            DWORD i;

-            for( i = 0; i < cbNeeded / sizeof( HMODULE ); i++ )

-            {

-                global_add( &first_automatic_object, hAddtnlMods[i] );

-            }

-        }

-        auto_ref_count++;

     }

     else

     {

+        HANDLE hCurrentProc;

+        DWORD dwProcModsBefore, dwProcModsAfter;

         CHAR lpFileName[MAX_PATH];

-        int i;

+        size_t i;

 

         /* MSDN says backslashes *must* be used instead of forward slashes. */

         for( i = 0 ; i < sizeof(lpFileName) - 1 ; i ++ )

@@ -276,6 +250,11 @@ void *dlopen( const char *file, int mode )
         }

         lpFileName[i] = '\0';

 

+        hCurrentProc = GetCurrentProcess( );

+

+        if( EnumProcessModules( hCurrentProc, NULL, 0, &dwProcModsBefore ) == 0 )

+            dwProcModsBefore = 0;

+

         /* POSIX says the search path is implementation-defined.

          * LOAD_WITH_ALTERED_SEARCH_PATH is used to make it behave more closely

          * to UNIX's search paths (start with system folders instead of current

@@ -284,17 +263,24 @@ void *dlopen( const char *file, int mode )
         hModule = LoadLibraryEx(lpFileName, NULL, 

                                 LOAD_WITH_ALTERED_SEARCH_PATH );

 

-        /* If the object was loaded with RTLD_GLOBAL, add it to list of global

-         * objects, so that its symbols may be retrieved even if the handle for

+        if( EnumProcessModules( hCurrentProc, NULL, 0, &dwProcModsAfter ) == 0 )

+            dwProcModsAfter = 0;

+

+        /* If the object was loaded with RTLD_LOCAL, add it to list of local

+         * objects, so that its symbols cannot be retrieved even if the handle for

          * the original program file is passed. POSIX says that if the same

          * file is specified in multiple invocations, and any of them are

          * RTLD_GLOBAL, even if any further invocations use RTLD_LOCAL, the

-         * symbols will remain global.

+         * symbols will remain global. If number of loaded modules was not

+         * changed after calling LoadLibraryEx(), it means that library was

+         * already loaded.

          */

         if( !hModule )

             save_err_str( lpFileName );

-        else if( (mode & RTLD_GLOBAL) )

-            global_add( &first_object, hModule );

+        else if( (mode & RTLD_LOCAL) && dwProcModsBefore != dwProcModsAfter )

+            local_add( hModule );

+        else if( !(mode & RTLD_LOCAL) && dwProcModsBefore == dwProcModsAfter )

+            local_rem( hModule );

     }

 

     /* Return to previous state of the error-mode bit flags. */

@@ -303,21 +289,6 @@ void *dlopen( const char *file, int mode )
     return (void *) hModule;

 }

 

-static void free_auto( )

-{

-    global_object *pobject = first_automatic_object.next;

-    if( pobject )

-    {

-        global_object *next;

-        for ( ; pobject; pobject = next )

-        {

-            next = pobject->next;

-            free( pobject );

-        }

-        first_automatic_object.next = NULL;

-    }

-}

-

 int dlclose( void *handle )

 {

     HMODULE hModule = (HMODULE) handle;

@@ -327,22 +298,11 @@ int dlclose( void *handle )
 

     ret = FreeLibrary( hModule );

 

-    /* If the object was loaded with RTLD_GLOBAL, remove it from list of global

+    /* If the object was loaded with RTLD_LOCAL, remove it from list of local

      * objects.

      */

     if( ret )

-    {

-        HMODULE cur = GetModuleHandle( NULL );

-        global_rem( &first_object, hModule );

-        if( hModule == cur )

-        {

-            auto_ref_count--;

-            if( auto_ref_count < 0 )

-                auto_ref_count = 0;

-            if( !auto_ref_count )

-                free_auto( );

-        }

-    }

+        local_rem( hModule );

     else

         save_err_ptr_str( handle );

 

@@ -356,6 +316,7 @@ void *dlsym( void *handle, const char *name )
 {

     FARPROC symbol;

     HMODULE hModule;

+    HANDLE hCurrentProc;

 

 #ifdef UNICODE

     wchar_t namew[MAX_PATH];

@@ -363,6 +324,7 @@ void *dlsym( void *handle, const char *name )
 #endif

 

     current_error = NULL;

+    hCurrentProc = GetCurrentProcess( );

 

     symbol = GetProcAddress( (HMODULE) handle, name );

 

@@ -377,25 +339,33 @@ void *dlsym( void *handle, const char *name )
 

     if( hModule == handle )

     {

-        global_object *pobject;

-

-        for( pobject = &first_object; pobject; pobject = pobject->next )

-        {

-            if( pobject->hModule )

-            {

-                symbol = GetProcAddress( pobject->hModule, name );

-                if( symbol != NULL )

-                    goto end;

-            }

-        }

+        HMODULE *modules;

+        DWORD cbNeeded;

+        DWORD dwSize;

+        size_t i;

 

-        for( pobject = &first_automatic_object; pobject; pobject = pobject->next )

+        /* GetModuleHandle( NULL ) only returns the current program file. So

+         * if we want to get ALL loaded module including those in linked DLLs,

+         * we have to use EnumProcessModules( ).

+         */

+        if( EnumProcessModules( hCurrentProc, NULL, 0, &dwSize ) != 0 )

         {

-            if( pobject->hModule )

+            modules = malloc( dwSize );

+            if( modules )

             {

-                symbol = GetProcAddress( pobject->hModule, name );

-                if( symbol != NULL )

-                    goto end;

+                if( EnumProcessModules( hCurrentProc, modules, dwSize, &cbNeeded ) != 0 && dwSize == cbNeeded )

+                {

+                    for( i = 0; i < dwSize / sizeof( HMODULE ); i++ )

+                    {

+                        if( local_search( modules[i] ) )

+                            continue;

+                        symbol = GetProcAddress( modules[i], name );

+                        if( symbol != NULL )

+                            goto end;

+                    }

+

+                }

+                free( modules );

             }

         }

     }

@@ -472,18 +442,8 @@ char *dlerror( void )
 BOOL WINAPI DllMain( HINSTANCE hinstDLL, DWORD fdwReason, LPVOID lpvReserved )

 {

     (void) hinstDLL;

-    /*

-     * https://msdn.microsoft.com/en-us/library/windows/desktop/ms682583(v=vs.85).aspx 

-     *

-     *     When handling DLL_PROCESS_DETACH, a DLL should free resources such as heap

-     *     memory only if the DLL is being unloaded dynamically (the lpReserved

-     *     parameter is NULL).

-     */

-    if( fdwReason == DLL_PROCESS_DETACH && !lpvReserved )

-    {

-        auto_ref_count = 0;

-        free_auto( );

-    }

+    (void) fdwReason;

+    (void) lpvReserved;

     return TRUE;

 }

 #endif

diff --git a/test.c b/test.c
index ba440da..10c655e 100644
--- a/test.c
+++ b/test.c
@@ -2,6 +2,7 @@
  * dlfcn-win32

  * Copyright (c) 2007-2009 Ramiro Polla

  * Copyright (c) 2014      Tiancheng "Timothy" Gu

+ * Copyright (c) 2019      Pali Rohár <pali.rohar@gmail.com>

  *

  * dlfcn-win32 is free software; you can redistribute it and/or

  * modify it under the terms of the GNU Lesser General Public

@@ -25,6 +26,7 @@
 #endif

 #include <stdio.h>

 #include <string.h>

+#include <windows.h>

 #include "dlfcn.h"

 

 /* If these dlclose's fails, we don't care as the handles are going to be

@@ -77,6 +79,7 @@ int main()
     size_t (*fwrite_local) ( const void *, size_t, size_t, FILE * );

     int (*nonexistentfunction)( void );

     int ret;

+    HMODULE library3;

 

 #ifdef _DEBUG

     _CrtSetReportMode(_CRT_WARN, _CRTDBG_MODE_FILE);

@@ -335,6 +338,15 @@ int main()
         printf("SUCCESS\tGot symbol from global handle: %p\n", function);

     

 

+    library3 = LoadLibraryA("testdll3.dll");

+    if (!library3)

+    {

+        printf( "ERROR\tCould not open library3 via WINAPI\n" );

+        RETURN_ERROR;

+    }

+    else

+        printf( "SUCCESS\tOpened library3 via WINAPI: %p\n", library3 );

+

     ret = dlclose( library );

     if( ret )

     {

@@ -346,6 +358,21 @@ int main()
     else

         printf( "SUCCESS\tClosed library.\n" );

 

+    function = dlsym(global, "function3");

+    if (!function)

+    {

+        error = dlerror();

+        printf("ERROR\tCould not get symbol from global handle: %s\n",

+            error ? error : "");

+        CLOSE_LIB;

+        CLOSE_GLOBAL;

+        RETURN_ERROR;

+    }

+    else

+        printf("SUCCESS\tGot symbol from global handle: %p\n", function);

+

+    RUNFUNC;

+

     ret = dlclose( global );

     if( ret )

     {

diff --git a/testdll3.c b/testdll3.c
new file mode 100644
index 0000000..3906e48
--- /dev/null
+++ b/testdll3.c
@@ -0,0 +1,38 @@
+/*

+ * dlfcn-win32

+ * Copyright (c) 2007 Ramiro Polla

+ * Copyright (c) 2019 Pali Rohár <pali.rohar@gmail.com>

+ *

+ * dlfcn-win32 is free software; you can redistribute it and/or

+ * modify it under the terms of the GNU Lesser General Public

+ * License as published by the Free Software Foundation; either

+ * version 2.1 of the License, or (at your option) any later version.

+ *

+ * dlfcn-win32 is distributed in the hope that it will be useful,

+ * but WITHOUT ANY WARRANTY; without even the implied warranty of

+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

+ * Lesser General Public License for more details.

+ *

+ * You should have received a copy of the GNU Lesser General Public

+ * License along with dlfcn-win32; if not, write to the Free Software

+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA

+ */

+

+#ifdef _DEBUG

+#define _CRTDBG_MAP_ALLOC

+#include <stdlib.h>

+#include <crtdbg.h>

+#endif

+#include <stdio.h>

+

+#if defined(_WIN32)

+#define EXPORT __declspec(dllexport)

+#else

+#define EXPORT

+#endif

+

+EXPORT int function3( void )

+{

+    printf( "Hello, world!\n" );

+    return 0;

+}