elf: Call __libc_early_init for reused namespaces (bug 29528)

libc_map is never reset to NULL, neither during dlclose nor on a
dlopen call which reuses the namespace structure.  As a result, if a
namespace is reused, its libc is not initialized properly.  The most
visible result is a crash in the <ctype.h> functions.

To prevent similar bugs on namespace reuse from surfacing,
unconditionally initialize the chosen namespace to zero using memset.

elf/Makefile

@@ -410,6 +410,7 @@ tests += \
   tst-dlmopen4 \
   tst-dlmopen-dlerror \
   tst-dlmopen-gethostbyname \
+  tst-dlmopen-twice \
   tst-dlopenfail \
   tst-dlopenfail-2 \
   tst-dlopenrpath \
@@ -839,6 +840,8 @@ modules-names += \
   tst-dlmopen1mod \
   tst-dlmopen-dlerror-mod \
   tst-dlmopen-gethostbyname-mod \
+  tst-dlmopen-twice-mod1 \
+  tst-dlmopen-twice-mod2 \
   tst-dlopenfaillinkmod \
   tst-dlopenfailmod1 \
   tst-dlopenfailmod2 \
@@ -2976,3 +2979,7 @@ $(objpfx)tst-audit-tlsdesc.out: $(objpfx)tst-auditmod-tlsdesc.so
 tst-audit-tlsdesc-ENV = LD_AUDIT=$(objpfx)tst-auditmod-tlsdesc.so
 $(objpfx)tst-audit-tlsdesc-dlopen.out: $(objpfx)tst-auditmod-tlsdesc.so
 tst-audit-tlsdesc-dlopen-ENV = LD_AUDIT=$(objpfx)tst-auditmod-tlsdesc.so
+
+$(objpfx)tst-dlmopen-twice.out: \
+  $(objpfx)tst-dlmopen-twice-mod1.so \
+  $(objpfx)tst-dlmopen-twice-mod2.so

elf/dl-open.c

@@ -844,11 +844,14 @@ _dl_open (const char *file, int mode, const void *caller_dlopen, Lmid_t nsid,
 	  _dl_signal_error (EINVAL, file, NULL, N_("\
 no more namespaces available for dlmopen()"));
 	}
-      else if (nsid == GL(dl_nns))
+
-	{
+      if (nsid == GL(dl_nns))
-	  __rtld_lock_initialize (GL(dl_ns)[nsid]._ns_unique_sym_table.lock);
+	++GL(dl_nns);
-	  ++GL(dl_nns);
+
-	}
+      /* Initialize the new namespace.  Most members are
+	 zero-initialized, only the lock needs special treatment.  */
+      memset (&GL(dl_ns)[nsid], 0, sizeof (GL(dl_ns)[nsid]));
+      __rtld_lock_initialize (GL(dl_ns)[nsid]._ns_unique_sym_table.lock);
 
       _dl_debug_update (nsid)->r_state = RT_CONSISTENT;
     }

elf/tst-dlmopen-twice-mod1.c

@@ -0,0 +1,37 @@
+/* Initialization of libc after dlmopen/dlclose/dlmopen (bug 29528).  Module 1.
+   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 <stdio.h>
+
+static void __attribute__ ((constructor))
+init (void)
+{
+  puts ("info: tst-dlmopen-twice-mod1.so loaded");
+  fflush (stdout);
+}
+
+static void __attribute__ ((destructor))
+fini (void)
+{
+  puts ("info: tst-dlmopen-twice-mod1.so about to be unloaded");
+  fflush (stdout);
+}
+
+/* Large allocation.  The second module does not have this, so it
+   should load libc at a different address.  */
+char large_allocate[16 * 1024 * 1024];

elf/tst-dlmopen-twice-mod2.c

@@ -0,0 +1,50 @@
+/* Initialization of libc after dlmopen/dlclose/dlmopen (bug 29528).  Module 2.
+   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 <ctype.h>
+#include <stdio.h>
+
+static void __attribute__ ((constructor))
+init (void)
+{
+  puts ("info: tst-dlmopen-twice-mod2.so loaded");
+  fflush (stdout);
+}
+
+static void __attribute__ ((destructor))
+fini (void)
+{
+  puts ("info: tst-dlmopen-twice-mod2.so about to be unloaded");
+  fflush (stdout);
+}
+
+int
+run_check (void)
+{
+  puts ("info: about to call isalpha");
+  fflush (stdout);
+
+  volatile char ch = 'a';
+  if (!isalpha (ch))
+    {
+      puts ("error: isalpha ('a') is not true");
+      fflush (stdout);
+      return 1;
+    }
+  return 0;
+}

elf/tst-dlmopen-twice.c

@@ -0,0 +1,34 @@
+/* Initialization of libc after dlmopen/dlclose/dlmopen (bug 29528).  Main.
+   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 <support/xdlfcn.h>
+#include <support/check.h>
+
+static int
+do_test (void)
+{
+  void *handle = xdlmopen (LM_ID_NEWLM, "tst-dlmopen-twice-mod1.so", RTLD_NOW);
+  xdlclose (handle);
+  handle = xdlmopen (LM_ID_NEWLM, "tst-dlmopen-twice-mod2.so", RTLD_NOW);
+  int (*run_check) (void) = xdlsym (handle, "run_check");
+  TEST_COMPARE (run_check (), 0);
+  xdlclose (handle);
+  return 0;
+}
+
+#include <support/test-driver.c>