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.

1 files changed, 37 insertions, 0 deletions

diff --git a/elf/tst-dlmopen-twice-mod1.c b/elf/tst-dlmopen-twice-mod1.c
new file mode 100644
index 0000000000..0eaf04948c
--- /dev/null
+++ b/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];