Core: replace RTLD_DEEPBIND (dlopen flag) with a new plugin flag

Using RTLD_DEEPBIND flag when loading plugin helps to solve issue
with some 3rd party libraries (e.g. librdkafka) if the library
redefines a common symbol. However, using this dlopen flag globally
for all plugins caused segfault when using C++ iostream (e.g.
"std::cout << "some text";)

Plugins can use IPX_PF_DEEPBIND flag in ipx_plugin_info to
instruct the collector to use RTLD_DEEPBIND when loading the plugin.

Author: Lukas955

include/ipfixcol2/plugins.h

@@ -135,6 +135,21 @@ typedef struct ipx_ctx_ext ipx_ctx_ext_t;
  */
 #define IPX_PT_OUTPUT 3U
 
+/**
+ * \def IPX_PF_DEEPBIND
+ * \brief Use deep bind when resolving symbols of a plugin (and additional depending libraries)
+ *
+ * Some plugins might depend on an external library which redefines one or more common symbols
+ * (e.g. thrd_create) used by the collector (or other plugins). Since common version of these
+ * symbols is resolved before any plugin is loaded, these redefined symbols are ignored.
+ * Therefore, the plugin (or third party libraries) might not be able to correctly work.
+ *
+ * This flag instructs the collector to use RTLD_DEEPBIND (see manual page of dlopen) which
+ * solves this issue. However, it might not be supported by non-glibc implementations
+ * (as it is a GNU extension) and might break some other functions. Use only if really required!
+ */
+#define IPX_PF_DEEPBIND 1U
+
 /**
  * \brief Identification of a plugin
  *
@@ -149,7 +164,7 @@ struct ipx_plugin_info {
     const char *dsc;
     /** Plugin type (one of #IPX_PT_INPUT, #IPX_PT_INTERMEDIATE, #IPX_PT_OUTPUT)              */
     uint16_t type;
-    /** Configuration flags (reserved for future use)                                         */
+    /** Configuration flags (zero or more IPX_PF_* values might be ORed here)                 */
     uint16_t flags;
     /** Plugin version string (like "1.2.3")                                                  */
     const char *version;

src/CMakeLists.txt

@@ -2,6 +2,9 @@ if (POLICY CMP0063)
     cmake_policy(SET CMP0063 NEW)
 endif()
 
+include(CheckSymbolExists)
+check_symbol_exists("RTLD_DEEPBIND" "dlfcn.h" HAVE_RTLD_DEEPBIND)
+
 # Configure a header file to pass some CMake variables
 configure_file(
     "${PROJECT_SOURCE_DIR}/src/build_config.h.in"

src/build_config.h.in

@@ -125,6 +125,9 @@
     #define IPX_BUILD_ARCH "unknown"
 #endif
 
+// Deep bind support
+#cmakedefine HAVE_RTLD_DEEPBIND
+
 /**@}*/
 
 #endif /* _BUILD_CONFIG_ */

src/core/configurator/plugin_mgr.cpp

@@ -207,7 +207,7 @@ ipx_plugin_mgr::cache_add_file(const char *path)
     dlerror();
 
     // Try to load the plugin (and unload it automatically)
-    const int flags = RTLD_LAZY | RTLD_LOCAL | RTLD_DEEPBIND;
+    const int flags = RTLD_LAZY | RTLD_LOCAL;
     auto delete_fn = [](void *handle) {dlclose(handle);};
     std::unique_ptr<void, std::function<void(void*)>> handle(dlopen(path, flags), delete_fn);
     if (!handle) {
@@ -308,7 +308,7 @@ ipx_plugin_mgr::plugin_list()
         dlerror();
 
         const char *path = cache_entry.path.c_str();
-        const int flags = RTLD_LAZY | RTLD_LOCAL | RTLD_DEEPBIND;
+        const int flags = RTLD_LAZY | RTLD_LOCAL;
         auto delete_fn = [](void *handle) {dlclose(handle);};
 
         std::unique_ptr<void, std::function<void(void*)>> handle(dlopen(path, flags), delete_fn);
@@ -348,6 +348,15 @@ ipx_plugin_mgr::plugin_list()
             continue;
         }
 
+        if (info->flags & IPX_PF_DEEPBIND) {
+#ifdef HAVE_RTLD_DEEPBIND
+            plugin_entry.msg_notes.emplace_back("Deep bind (RTLD_DEEPBIND) required");
+#else
+            plugin_entry.msg_warning.emplace_back(
+                "Deep bind (RTLD_DEEPBIND) required but not supported by C library");
+#endif
+        }
+
         if (!version_ok) {
             std::stringstream ss;
             ss << "incompatible with this collector version (min. required: ";
@@ -503,18 +512,44 @@ ipx_plugin_mgr::version_check(const std::string &min_version)
  * \param[in] path        Path to the plugin to load
  * \param[in] auto_unload Automatically unload the plugin on destroy (can be changed later)
  */
-ipx_plugin_mgr::plugin::plugin(const std::string &path,  bool auto_unload)
+ipx_plugin_mgr::plugin::plugin(const std::string &path, bool auto_unload)
     : unload(auto_unload)
 {
+    auto delete_fn = [](void *handle) {dlclose(handle);};
+    std::unique_ptr<void, std::function<void(void*)>> handle_wrap(nullptr, delete_fn);
+
+    const struct ipx_plugin_info *info;
+    int load_flags = RTLD_NOW | RTLD_LOCAL;
+
     // Initialize default parameters
     ref_cnt = 0;
     std::memset(&cbs, 0, sizeof(cbs));
 
-    // Load the plugin
-    auto delete_fn = [](void *handle) {dlclose(handle);};
-    int flags = RTLD_NOW | RTLD_LOCAL | RTLD_DEEPBIND;
-    dlerror(); // Clear all errors first
-    std::unique_ptr<void, std::function<void(void*)>> handle_wrap(dlopen(path.c_str(), flags), delete_fn);
+    // Determine whether or not to use deep bind
+    dlerror();
+    handle_wrap.reset(dlopen(path.c_str(), RTLD_LAZY | RTLD_LOCAL));
+    if (!handle_wrap) {
+        // Failed to open the file
+        std::string err_msg = "Failed to load a plugin from '" + path + "': " + dlerror();
+        throw ipx_plugin_mgr::error(err_msg);
+    }
+
+    *(void **)(&info) = symbol_get(handle_wrap.get(), "ipx_plugin_info", false);
+    if (info->flags & IPX_PF_DEEPBIND) {
+#ifdef HAVE_RTLD_DEEPBIND
+        IPX_DEBUG(comp_str, "Loading plugin from '%s' using RTLD_DEEPBIND flag!", path.c_str());
+        load_flags |= RTLD_DEEPBIND;
+#else
+        std::string err_msg = "Deep bind (RTLD_DEEPBIND) required but not supported by C library";
+        throw ipx_plugin_mgr::error("Failed to load a plugin from '" + path + "': " + err_msg);
+#endif
+    }
+
+    // Close the plugin and reload it
+    handle_wrap.reset();
+
+    dlerror();
+    handle_wrap.reset(dlopen(path.c_str(), load_flags));
     if (!handle_wrap) {
         // Failed to open the file
         std::string err_msg = "Failed to load a plugin from '" + path + "': " + dlerror();