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

1 files changed, 1 insertions, 0 deletions

diff --git a/libexec/rtld-elf/rtld.h b/libexec/rtld-elf/rtld.h
index 6bae2f0..faa84e2 100644
--- a/libexec/rtld-elf/rtld.h
+++ b/libexec/rtld-elf/rtld.h
@@ -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 (%) */