svn commit: r214728 - head/libexec/rtld-elf

[Konstantin Belousov]

Author: kib
Date: Wed Nov  3 09:23:08 2010
New Revision: 214728
URL: http://svn.freebsd.org/changeset/base/214728

Log:
  If dlopen() is called for the dso that has been already loaded as a
  dependency, then the dso never has its DAG initialized. Empty DAG
  makes ref_dag() call in dlopen() a nop, and the dso refcount is off
  by one.
  
  Initialize the DAG on the first dlopen() call, using a boolean flag
  to prevent double initialization.
  
  From the PR (edited):
  Assume we have a library liba.so, containing a function a(), and a
  library libb.so, containing function b(). liba.so needs functionality
  from libb.so, so liba.so links in libb.so.
  
  An application doesn't know about the relation between these libraries,
  but needs to call a() and b(). It dlopen()s liba.so and obtains a
  pointer to a(), then it dlopen()s libb.so and obtains a pointer to b().
  
  As soon as the application doesn't need a() anymore, it dlclose()s liba.so.
  
  Expected result: the pointer to b() is still valid and can be called
  Actual result: the pointer to b() has become invalid, even though the
  application did not dlclose() the handle to libb.so. On calling b(), the
  application crashes with a segmentation fault.
  
  PR:	misc/151861
  Based on patch by:	jh
  Reviewed by:	kan
  Tested by:	Arjan van Leeuwen <freebsd-maintainer opera com>
  MFC after:	1 week

Modified:
  head/libexec/rtld-elf/rtld.c
  head/libexec/rtld-elf/rtld.h

Modified: head/libexec/rtld-elf/rtld.c
==============================================================================
--- head/libexec/rtld-elf/rtld.c	Wed Nov  3 08:34:00 2010	(r214727)
+++ head/libexec/rtld-elf/rtld.c	Wed Nov  3 09:23:08 2010	(r214728)
@@ -1275,8 +1275,11 @@ init_dag(Obj_Entry *root)
 {
     DoneList donelist;
 
+    if (root->dag_inited)
+	    return;
     donelist_init(&donelist);
     init_dag1(root, root, &donelist);
+    root->dag_inited = true;
 }
 
 static void
@@ -2045,8 +2048,16 @@ dlopen(const char *name, int mode)
 	    }
 	} else {
 
-	    /* Bump the reference counts for objects on this DAG. */
-	    ref_dag(obj);
+	    /*
+	     * Bump the reference counts for objects on this DAG.  If
+	     * this is the first dlopen() call for the object that was
+	     * already loaded as a dependency, initialize the dag
+	     * starting at it.
+	     */
+	    if (obj->dl_refcount == 1)
+		init_dag(obj);
+	    else
+		ref_dag(obj);
 
 	    if (ld_tracing)
 		goto trace;

Modified: head/libexec/rtld-elf/rtld.h
==============================================================================
--- head/libexec/rtld-elf/rtld.h	Wed Nov  3 08:34:00 2010	(r214727)
+++ head/libexec/rtld-elf/rtld.h	Wed Nov  3 09:23:08 2010	(r214728)
@@ -222,6 +222,7 @@ typedef struct Struct_Obj_Entry {
     bool ref_nodel : 1;		/* Refcount increased to prevent dlclose */
     bool init_scanned: 1;	/* Object is already on init list. */
     bool on_fini_list: 1;	/* Object is already on fini list. */
+    bool dag_inited : 1;	/* Object has its DAG initialized. */
 
     struct link_map linkmap;	/* For GDB and dlinfo() */
     Objlist dldags;		/* Object belongs to these dlopened DAGs (%) */