Re: [PATCH] dlfcn: Guard __dlerror_main_freeres with __libc_once_get (once) [BZ# 24476]

[Mark Wielaard <mark at klomp dot org>]

On Thu, 2019-05-09 at 14:30 -0400, Carlos O'Donell wrote:
> In summary:
> - Check in __dlerror_main_freeres should be: 
>   if (__libc_once_get (once) && static_buf == NULL)
> - Fixup check in __dlerror:
>   if (static_buf != NULL)
>     result = static_buf;
> 
> What you're fixing here is all the conditionals that appear
> wrong in the case that dlerror is never called or the other
> similar case (which can cause valgrind to fail) which is
> if __libc_key_create fails.

Makes sense. Done as follows:

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

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));