[2.29 COMMITTED] dlfcn: Guard __dlerror_main_freeres with __libc_once_get (once) [BZ#24476]

[Mark Wielaard <mjw@redhat.com>]

From: Mark Wielaard <mark@klomp.org>

dlerror.c (__dlerror_main_freeres) will try to free resources which only
have been initialized when init () has been called. That function is
called when resources are needed using __libc_once (once, init) where
once is a __libc_once_define (static, once) in the dlerror.c file.
Trying to free those resources if init () hasn't been called will
produce errors under valgrind memcheck. So guard the freeing of those
resources using __libc_once_get (once) and make sure we have a valid
key. Also add a similar guard to __dlerror ().

	* dlfcn/dlerror.c (__dlerror_main_freeres): Guard using
	__libc_once_get (once) and static_bug == NULL.
	(__dlerror): Check we have a valid key, set result to static_buf
	otherwise.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>
(cherry picked from commit 11b451c8868d8a2b0edc5dfd44fc58d9ee538be0)

diff --git a/dlfcn/dlerror.c b/dlfcn/dlerror.c
index 2737658..ca42c12 100644
--- a/dlfcn/dlerror.c
+++ b/dlfcn/dlerror.c
@@ -72,9 +72,16 @@ __dlerror (void)
   __libc_once (once, init);
 
   /* Get error string.  */
-  result = (struct dl_action_result *) __libc_getspecific (key);
-  if (result == NULL)
-    result = &last_result;
+  if (static_buf != NULL)
+    result = static_buf;
+  else
+    {
+      /* init () has been run and we don't use the static buffer.
+	 So we have a valid key.  */
+      result = (struct dl_action_result *) __libc_getspecific (key);
+      if (result == NULL)
+	result = &last_result;
+    }
 
   /* Test whether we already returned the string.  */
   if (result->returned != 0)
@@ -230,13 +237,19 @@ free_key_mem (void *mem)
 void
 __dlerror_main_freeres (void)
 {
-  void *mem;
   /* Free the global memory if used.  */
   check_free (&last_result);
-  /* Free the TSD memory if used.  */
-  mem = __libc_getspecific (key);
-  if (mem != NULL)
-    free_key_mem (mem);
+
+  if (__libc_once_get (once) && static_buf == NULL)
+    {
+      /* init () has been run and we don't use the static buffer.
+	 So we have a valid key.  */
+      void *mem;
+      /* Free the TSD memory if used.  */
+      mem = __libc_getspecific (key);
+      if (mem != NULL)
+	free_key_mem (mem);
+    }
 }
 
 struct dlfcn_hook *_dlfcn_hook __attribute__((nocommon));