elf: Test dlopen (NULL, RTLD_LAZY) from an ELF constructor

This call must not complete initialization of all shared objects
in the global scope because the ELF constructor which makes the call
likely has not finished initialization.  Calling more constructors
at this point would expose those to a partially constructed
dependency.

This completes the revert of commit 9897ced8e7
("elf: Run constructors on cyclic recursive dlopen (bug 31986)").

elf/Makefile

@@ -417,6 +417,7 @@ tests += \
   tst-dlmopen3 \
   tst-dlmopen4 \
   tst-dlopen-auditdup \
+  tst-dlopen-constructor-null \
   tst-dlopen-self \
   tst-dlopen-tlsmodid \
   tst-dlopen-tlsreinit1 \
@@ -908,6 +909,8 @@ modules-names += \
   tst-dlmopen1mod \
   tst-dlopen-auditdup-auditmod \
   tst-dlopen-auditdupmod \
+  tst-dlopen-constructor-null-mod1 \
+  tst-dlopen-constructor-null-mod2 \
   tst-dlopen-tlsreinitmod1 \
   tst-dlopen-tlsreinitmod2 \
   tst-dlopen-tlsreinitmod3 \
@@ -3433,3 +3436,9 @@ LDFLAGS-tst-version-hash-zero-linkmod.so = \
 $(objpfx)tst-version-hash-zero-refmod.so: \
   $(objpfx)tst-version-hash-zero-linkmod.so
 tst-version-hash-zero-refmod.so-no-z-defs = yes
+
+$(objpfx)tst-dlopen-constructor-null: \
+  $(objpfx)tst-dlopen-constructor-null-mod1.so \
+  $(objpfx)tst-dlopen-constructor-null-mod2.so
+$(objpfx)tst-dlopen-constructor-null-mod2.so: \
+  $(objpfx)tst-dlopen-constructor-null-mod1.so

elf/dl-open.c

@@ -587,6 +587,16 @@ dl_open_worker_begin (void *a)
       if ((mode & RTLD_GLOBAL) && new->l_global == 0)
 	add_to_global_update (new);
 
+      /* It is not possible to run the ELF constructor for the new
+	 link map if it has not executed yet: If this dlopen call came
+	 from an ELF constructor that has not put that object into a
+	 consistent state, completing initialization for the entire
+	 scope will expose objects that have this partially
+	 constructed object among its dependencies to this
+	 inconsistent state.  This could happen even with a benign
+	 dlopen (NULL, RTLD_LAZY) call from a constructor of an
+	 initially loaded shared object.  */
+
       return;
     }
 

elf/tst-dlopen-constructor-null-mod1.c

@@ -0,0 +1,55 @@
+/* Module calling dlopen (NULL, RTLD_LAZY) to obtain the global scope.
+   Copyright (C) 2024 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 <stddef.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+int mod1_status;
+
+static void __attribute__ ((constructor))
+init (void)
+{
+  puts ("info: tst-dlopen-constructor-null-mod1.so constructor");
+
+  void *handle = dlopen (NULL, RTLD_LAZY);
+  if (handle == NULL)
+    {
+      printf ("error: %s\n", dlerror ());
+      exit (1);
+    }
+  puts ("info: dlopen returned");
+  if (dlsym (handle, "malloc") != malloc)
+    {
+      puts ("error: dlsym did not produce expected result");
+      exit (1);
+    }
+  dlclose (handle);
+
+  /* Check that the second module's constructor has not executed.   */
+  if (getenv ("mod2_status") != NULL)
+    {
+      printf ("error: mod2_status environment variable set: %s\n",
+              getenv ("mod2_status"));
+      exit (1);
+    }
+
+  /* Communicate to the second module that the constructor executed.   */
+  mod1_status = 1;
+}

elf/tst-dlopen-constructor-null-mod2.c

@@ -0,0 +1,37 @@
+/* Module whose constructor should not be invoked by dlopen (NULL, RTLD_LAZY).
+   Copyright (C) 2024 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 <stdio.h>
+#include <stdlib.h>
+
+extern int mod1_status;
+int mod2_status;
+
+static void __attribute__ ((constructor))
+init (void)
+{
+  printf ("info: tst-dlopen-constructor-null-mod2.so constructor"
+          " (mod1_status=%d)", mod1_status);
+  if (!(mod1_status == 1 && mod2_status == 0))
+    {
+      puts ("error: mod1_status == 1 && mod2_status == 0 expected");
+      exit (1);
+    }
+  setenv ("mod2_status", "constructed", 1);
+  mod2_status = 1;
+}

elf/tst-dlopen-constructor-null.c

@@ -0,0 +1,38 @@
+/* Verify that dlopen (NULL, RTLD_LAZY) does not complete initialization.
+   Copyright (C) 2024 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/>.  */
+
+/* This test mimics what the glvndSetupPthreads function in libglvnd
+   does. */
+
+#include <stdlib.h>
+#include <support/check.h>
+
+/* Defined and initialized in the shared objects.  */
+extern int mod1_status;
+extern int mod2_status;
+
+static int
+do_test (void)
+{
+  TEST_COMPARE (mod1_status, 1);
+  TEST_COMPARE (mod2_status, 1);
+  TEST_COMPARE_STRING (getenv ("mod2_status"), "constructed");
+  return 0;
+}
+
+#include <support/test-driver.c>