ld.so: Examine GLRO to detect inactive loader [BZ #20204]

GLRO (_rtld_global_ro) is read-only after initialization and can
therefore not be patched at run time, unlike the hook table addresses
and their contents, so this is a desirable hardening feature.

The hooks are only needed if ld.so has not been initialized, and this
happens only after static dlopen (dlmopen uses a single ld.so object
across all namespaces).

Reviewed-by: Carlos O'Donell <carlos@redhat.com>

1 files changed, 2 insertions, 1 deletions

diff --git a/libio/vtables.c b/libio/vtables.c
index 41b48db98c..4d4afa2efc 100644
--- a/libio/vtables.c
+++ b/libio/vtables.c
@@ -19,6 +19,7 @@
 #include <dlfcn.h>
 #include <libioP.h>
 #include <stdio.h>
+#include <ldsodefs.h>
 
 #ifdef SHARED
 
@@ -54,7 +55,7 @@ _IO_vtable_check (void)
   {
     Dl_info di;
     struct link_map *l;
-    if (_dl_open_hook != NULL
+    if (!rtld_active ()
         || (_dl_addr (_IO_vtable_check, &di, &l, NULL) != 0
             && l->l_ns != LM_ID_BASE))
       return;