dlfcn: dlerror needs to call free from the base namespace [BZ #24773]

Calling free directly may end up freeing a pointer allocated by the
dynamic loader using malloc from libc.so in the base namespace using
the allocator from libc.so in a secondary namespace, which results in
crashes.

This commit redirects the free call through GLRO and the dynamic
linker, to reach the correct namespace.  It also cleans up the dlerror
handling along the way, so that pthread_setspecific is no longer
needed (which avoids triggering bug 24774).

1 files changed, 39 insertions, 0 deletions

diff --git a/dlfcn/libc_dlerror_result.c b/dlfcn/libc_dlerror_result.c
new file mode 100644
index 0000000000..99747186b9
--- /dev/null
+++ b/dlfcn/libc_dlerror_result.c
@@ -0,0 +1,39 @@
+/* Thread-local variable holding the dlerror result.
+   Copyright (C) 2021 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library 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.
+
+   The GNU C Library 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 the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <dlerror.h>
+
+/* This pointer is either NULL, dl_action_result_malloc_failed (), or
+   has been allocated using malloc by the namespace that also contains
+   this instance of the thread-local variable.  */
+__thread struct dl_action_result *__libc_dlerror_result attribute_tls_model_ie;
+
+/* Called during thread shutdown to free resources.  */
+void
+__libc_dlerror_result_free (void)
+{
+  if (__libc_dlerror_result != NULL)
+    {
+      if (__libc_dlerror_result != dl_action_result_malloc_failed)
+        {
+          dl_action_result_errstring_free (__libc_dlerror_result);
+          free (__libc_dlerror_result);
+        }
+      __libc_dlerror_result = NULL;
+    }
+}