dlfcn: Do not use rtld_active () to determine ld.so state (bug 29078)

When audit modules are loaded, ld.so initialization is not yet
complete, and rtld_active () returns false even though ld.so is
mostly working.  Instead, the static dlopen hook is used, but that
does not work at all because this is not a static dlopen situation.

Commit 466c1ea15f461edb8e3ffaf5d86d708876343bbf ("dlfcn: Rework
static dlopen hooks") moved the hook pointer into _rtld_global_ro,
which means that separate protection is not needed anymore and the
hook pointer can be checked directly.

The guard for disabling libio vtable hardening in _IO_vtable_check
should stay for now.

Fixes commit 8e1472d2c1e25e6eabc2059170731365f6d5b3d1 ("ld.so:
Examine GLRO to detect inactive loader [BZ #20204]").

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

4 files changed, 149 insertions, 4 deletions

diff --git a/elf/Makefile b/elf/Makefile
index 8ed6c3b0b1..e4907d5de9 100644
--- a/elf/Makefile
+++ b/elf/Makefile
@@ -390,6 +390,7 @@ tests += \
   tst-audit24d \
   tst-audit25a \
   tst-audit25b \
+  tst-audit26 \
   tst-auditmany \
   tst-auxobj \
   tst-auxobj-dlopen \
@@ -767,6 +768,7 @@ modules-names = \
   tst-auditmod24c \
   tst-auditmod24d \
   tst-auditmod25 \
+  tst-auditmod26 \
   tst-auxvalmod \
   tst-big-note-lib \
   tst-deep1mod1 \
@@ -2286,6 +2288,10 @@ $(objpfx)tst-audit25b: $(objpfx)tst-audit25mod1.so \
 LDFLAGS-tst-audit25b = -Wl,-z,now
 tst-audit25b-ARGS = -- $(host-test-program-cmd)
 
+$(objpfx)tst-audit26.out: $(objpfx)tst-auditmod26.so
+$(objpfx)tst-auditmod26.so: $(libsupport)
+tst-audit26-ENV = LD_AUDIT=$(objpfx)tst-auditmod26.so
+
 # tst-sonamemove links against an older implementation of the library.
 LDFLAGS-tst-sonamemove-linkmod1.so = \
   -Wl,--version-script=tst-sonamemove-linkmod1.map \
diff --git a/elf/dl-libc.c b/elf/dl-libc.c
index a7180d0af8..266e068da6 100644
--- a/elf/dl-libc.c
+++ b/elf/dl-libc.c
@@ -156,7 +156,7 @@ __libc_dlopen_mode (const char *name, int mode)
   args.caller_dlopen = RETURN_ADDRESS (0);
 
 #ifdef SHARED
-  if (!rtld_active ())
+  if (GLRO (dl_dlfcn_hook) != NULL)
     return GLRO (dl_dlfcn_hook)->libc_dlopen_mode (name, mode);
 #endif
   return dlerror_run (do_dlopen, &args) ? NULL : (void *) args.map;
@@ -184,7 +184,7 @@ __libc_dlsym (void *map, const char *name)
   args.name = name;
 
 #ifdef SHARED
-  if (!rtld_active ())
+  if (GLRO (dl_dlfcn_hook) != NULL)
     return GLRO (dl_dlfcn_hook)->libc_dlsym (map, name);
 #endif
   return (dlerror_run (do_dlsym, &args) ? NULL
@@ -198,7 +198,7 @@ void *
 __libc_dlvsym (void *map, const char *name, const char *version)
 {
 #ifdef SHARED
-  if (!rtld_active ())
+  if (GLRO (dl_dlfcn_hook) != NULL)
     return GLRO (dl_dlfcn_hook)->libc_dlvsym (map, name, version);
 #endif
 
@@ -221,7 +221,7 @@ int
 __libc_dlclose (void *map)
 {
 #ifdef SHARED
-  if (!rtld_active ())
+  if (GLRO (dl_dlfcn_hook) != NULL)
     return GLRO (dl_dlfcn_hook)->libc_dlclose (map);
 #endif
   return dlerror_run (do_dlclose, map);
diff --git a/elf/tst-audit26.c b/elf/tst-audit26.c
new file mode 100644
index 0000000000..3f920e83ba
--- /dev/null
+++ b/elf/tst-audit26.c
@@ -0,0 +1,35 @@
+/* Check the usability of <dlfcn.h> functions in audit modules.
+   Copyright (C) 2022 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <gnu/lib-names.h>
+
+#include <support/check.h>
+#include <support/xdlfcn.h>
+
+static int
+do_test (void)
+{
+  /* Check that the audit module has been loaded.  */
+  void *handle = xdlopen ("mapped to libc", RTLD_LOCAL | RTLD_NOW);
+  TEST_VERIFY (handle
+	       == xdlopen (LIBC_SO, RTLD_LOCAL | RTLD_NOW | RTLD_NOLOAD));
+
+  return 0;
+}
+
+#include <support/test-driver.c>
diff --git a/elf/tst-auditmod26.c b/elf/tst-auditmod26.c
new file mode 100644
index 0000000000..db7ba95abe
--- /dev/null
+++ b/elf/tst-auditmod26.c
@@ -0,0 +1,104 @@
+/* Check the usability of <dlfcn.h> functions in audit modules.  Audit module.
+   Copyright (C) 2022 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <dlfcn.h>
+#include <first-versions.h>
+#include <gnu/lib-names.h>
+#include <link.h>
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+
+#include <support/check.h>
+#include <support/xdlfcn.h>
+
+unsigned int
+la_version (unsigned int current)
+{
+  /* Exercise various <dlfcn.h> functions.  */
+
+  /* Check dlopen, dlsym, dlclose.   */
+  void *handle = xdlopen (LIBM_SO, RTLD_LOCAL | RTLD_NOW);
+  void *ptr = xdlsym (handle, "sincos");
+  TEST_VERIFY (ptr != NULL);
+  ptr = dlsym (handle, "SINCOS");
+  TEST_VERIFY (ptr == NULL);
+  const char *message = dlerror ();
+  TEST_VERIFY (strstr (message, ": undefined symbol: SINCOS") != NULL);
+  ptr = dlsym (handle, "SINCOS");
+  TEST_VERIFY (ptr == NULL);
+  xdlclose (handle);
+  TEST_COMPARE_STRING (dlerror (), NULL);
+
+  handle = xdlopen (LIBC_SO, RTLD_LOCAL | RTLD_NOW | RTLD_NOLOAD);
+
+  /* Check dlvsym.  _exit is unlikely to gain another symbol
+     version.  */
+  TEST_VERIFY (xdlsym (handle, "_exit")
+               == xdlvsym (handle, "_exit", FIRST_VERSION_libc__exit_STRING));
+
+  /* Check dlinfo.  */
+  {
+    void *handle2 = NULL;
+    TEST_COMPARE (dlinfo (handle, RTLD_DI_LINKMAP, &handle2), 0);
+    TEST_VERIFY (handle2 == handle);
+  }
+
+  /* Check dladdr and dladdr1.  */
+  Dl_info info = { };
+  TEST_VERIFY (dladdr (&_exit, &info) != 0);
+  if (strcmp (info.dli_sname, "_Exit") != 0) /* _Exit is an alias.  */
+    TEST_COMPARE_STRING (info.dli_sname, "_exit");
+  TEST_VERIFY (info.dli_saddr == &_exit);
+  TEST_VERIFY (strstr (info.dli_fname, LIBC_SO));
+  void *extra_info;
+  memset (&info, 0, sizeof (info));
+  TEST_VERIFY (dladdr1 (&_exit, &info, &extra_info, RTLD_DL_LINKMAP) != 0);
+  TEST_VERIFY (extra_info == handle);
+
+  /* Verify that dlmopen creates a new namespace.  */
+  void *dlmopen_handle = xdlmopen (LM_ID_NEWLM, LIBC_SO, RTLD_NOW);
+  TEST_VERIFY (dlmopen_handle != handle);
+  memset (&info, 0, sizeof (info));
+  extra_info = NULL;
+  ptr = xdlsym (dlmopen_handle, "_exit");
+  TEST_VERIFY (dladdr1 (ptr, &info, &extra_info, RTLD_DL_LINKMAP) != 0);
+  TEST_VERIFY (extra_info == dlmopen_handle);
+  xdlclose (dlmopen_handle);
+
+  /* Terminate the process with an error state.  This does not happen
+     automatically because the audit module state is not shared with
+     the main program.  */
+  if (support_record_failure_is_failed ())
+    {
+      fflush (stdout);
+      fflush (stderr);
+      _exit (1);
+    }
+
+  return LAV_CURRENT;
+}
+
+char *
+la_objsearch (const char *name, uintptr_t *cookie, unsigned int flag)
+{
+  if (strcmp (name, "mapped to libc") == 0)
+    return (char *) LIBC_SO;
+  else
+    return (char *) name;
+}