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>

10 files changed, 12 insertions, 10 deletions

diff --git a/dlfcn/dladdr.c b/dlfcn/dladdr.c
index 1753434..1bebd00 100644
--- a/dlfcn/dladdr.c
+++ b/dlfcn/dladdr.c
@@ -17,6 +17,7 @@
    <http://www.gnu.org/licenses/>.  */
 
 #include <dlfcn.h>
+#include <ldsodefs.h>
 
 #if !defined SHARED && IS_IN (libdl)
 
@@ -32,7 +33,7 @@ int
 __dladdr (const void *address, Dl_info *info)
 {
 # ifdef SHARED
-  if (__glibc_unlikely (_dlfcn_hook != NULL))
+  if (!rtld_active ())
     return _dlfcn_hook->dladdr (address, info);
 # endif
   return _dl_addr (address, info, NULL, NULL);
diff --git a/dlfcn/dladdr1.c b/dlfcn/dladdr1.c
index a19f9fd..901cf43 100644
--- a/dlfcn/dladdr1.c
+++ b/dlfcn/dladdr1.c
@@ -17,6 +17,7 @@
    <http://www.gnu.org/licenses/>.  */
 
 #include <dlfcn.h>
+#include <ldsodefs.h>
 
 #if !defined SHARED && IS_IN (libdl)
 
@@ -32,7 +33,7 @@ int
 __dladdr1 (const void *address, Dl_info *info, void **extra, int flags)
 {
 # ifdef SHARED
-  if (__glibc_unlikely (_dlfcn_hook != NULL))
+  if (!rtld_active ())
     return _dlfcn_hook->dladdr1 (address, info, extra, flags);
 # endif
 
diff --git a/dlfcn/dlclose.c b/dlfcn/dlclose.c
index da66e20..223887d 100644
--- a/dlfcn/dlclose.c
+++ b/dlfcn/dlclose.c
@@ -39,7 +39,7 @@ int
 __dlclose (void *handle)
 {
 # ifdef SHARED
-  if (__glibc_unlikely (_dlfcn_hook != NULL))
+  if (!rtld_active ())
     return _dlfcn_hook->dlclose (handle);
 # endif
 
diff --git a/dlfcn/dlerror.c b/dlfcn/dlerror.c
index fb5012e..b33c050 100644
--- a/dlfcn/dlerror.c
+++ b/dlfcn/dlerror.c
@@ -63,7 +63,7 @@ __dlerror (void)
   struct dl_action_result *result;
 
 # ifdef SHARED
-  if (__glibc_unlikely (_dlfcn_hook != NULL))
+  if (!rtld_active ())
     return _dlfcn_hook->dlerror ();
 # endif
 
diff --git a/dlfcn/dlinfo.c b/dlfcn/dlinfo.c
index a34e947..b011257 100644
--- a/dlfcn/dlinfo.c
+++ b/dlfcn/dlinfo.c
@@ -111,7 +111,7 @@ int
 __dlinfo (void *handle, int request, void *arg DL_CALLER_DECL)
 {
 # ifdef SHARED
-  if (__glibc_unlikely (_dlfcn_hook != NULL))
+  if (!rtld_active ())
     return _dlfcn_hook->dlinfo (handle, request, arg,
 				DL_CALLER);
 # endif
diff --git a/dlfcn/dlmopen.c b/dlfcn/dlmopen.c
index 07d59ad..58f88bb 100644
--- a/dlfcn/dlmopen.c
+++ b/dlfcn/dlmopen.c
@@ -79,7 +79,7 @@ void *
 __dlmopen (Lmid_t nsid, const char *file, int mode DL_CALLER_DECL)
 {
 # ifdef SHARED
-  if (__glibc_unlikely (_dlfcn_hook != NULL))
+  if (!rtld_active ())
     return _dlfcn_hook->dlmopen (nsid, file, mode, RETURN_ADDRESS (0));
 # endif
 
diff --git a/dlfcn/dlopen.c b/dlfcn/dlopen.c
index 2212065..73651a8 100644
--- a/dlfcn/dlopen.c
+++ b/dlfcn/dlopen.c
@@ -74,7 +74,7 @@ void *
 __dlopen (const char *file, int mode DL_CALLER_DECL)
 {
 # ifdef SHARED
-  if (__glibc_unlikely (_dlfcn_hook != NULL))
+  if (!rtld_active ())
     return _dlfcn_hook->dlopen (file, mode, DL_CALLER);
 # endif
 
diff --git a/dlfcn/dlopenold.c b/dlfcn/dlopenold.c
index a3db500..d899c4e 100644
--- a/dlfcn/dlopenold.c
+++ b/dlfcn/dlopenold.c
@@ -70,7 +70,7 @@ __dlopen_nocheck (const char *file, int mode)
     mode |= RTLD_LAZY;
   args.mode = mode;
 
-  if (__glibc_unlikely (_dlfcn_hook != NULL))
+  if (!rtld_active ())
     return _dlfcn_hook->dlopen (file, mode, RETURN_ADDRESS (0));
 
   return _dlerror_run (dlopen_doit, &args) ? NULL : args.new;
diff --git a/dlfcn/dlsym.c b/dlfcn/dlsym.c
index 7976c5f..19733a0 100644
--- a/dlfcn/dlsym.c
+++ b/dlfcn/dlsym.c
@@ -55,7 +55,7 @@ void *
 __dlsym (void *handle, const char *name DL_CALLER_DECL)
 {
 # ifdef SHARED
-  if (__glibc_unlikely (_dlfcn_hook != NULL))
+  if (!rtld_active ())
     return _dlfcn_hook->dlsym (handle, name, DL_CALLER);
 # endif
 
diff --git a/dlfcn/dlvsym.c b/dlfcn/dlvsym.c
index 5ed220b..ad46b65 100644
--- a/dlfcn/dlvsym.c
+++ b/dlfcn/dlvsym.c
@@ -58,7 +58,7 @@ __dlvsym (void *handle, const char *name, const char *version_str
 	  DL_CALLER_DECL)
 {
 # ifdef SHARED
-  if (__glibc_unlikely (_dlfcn_hook != NULL))
+  if (!rtld_active ())
     return _dlfcn_hook->dlvsym (handle, name, version_str, DL_CALLER);
 # endif