elf: Add tst-ldconfig-ld_so_conf-update test

Test ldconfig after /etc/ld.so.conf update and verify a running process
 observes changes to /etc/ld.so.cache.
 The test uses the test-in-container framework.

 Reviewed-by: Arjun Shankar <arjun@redhat.com>

elf/Makefile

@@ -162,8 +162,9 @@ tests-static-internal := tst-tls1-static tst-tls2-static \
 CRT-tst-tls1-static-non-pie := $(csu-objpfx)crt1.o
 tst-tls1-static-non-pie-no-pie = yes
 
-tests-container = \
-			  tst-ldconfig-bad-aux-cache
+tests-container := \
+			  tst-ldconfig-bad-aux-cache \
+			  tst-ldconfig-ld_so_conf-update
 
 tests := tst-tls9 tst-leaks1 \
 	tst-array1 tst-array2 tst-array3 tst-array4 tst-array5 \
@@ -309,7 +310,8 @@ modules-names = testobj1 testobj2 testobj3 testobj4 testobj5 testobj6 \
 		tst-auditmanymod4 tst-auditmanymod5 tst-auditmanymod6 \
 		tst-auditmanymod7 tst-auditmanymod8 tst-auditmanymod9 \
 		tst-initlazyfailmod tst-finilazyfailmod \
-		tst-dlopenfailmod1 tst-dlopenfaillinkmod tst-dlopenfailmod2
+		tst-dlopenfailmod1 tst-dlopenfaillinkmod tst-dlopenfailmod2 \
+		tst-ldconfig-ld-mod
 # Most modules build with _ISOMAC defined, but those filtered out
 # depend on internal headers.
 modules-names-tests = $(filter-out ifuncmod% tst-libc_dlvsym-dso tst-tlsmod%,\
@@ -1688,3 +1690,6 @@ $(objpfx)tst-dlopen-nodelete-reloc-mod17.so: \
   $(objpfx)tst-dlopen-nodelete-reloc-mod15.so \
   $(objpfx)tst-dlopen-nodelete-reloc-mod16.so
 LDFLAGS-tst-dlopen-nodelete-reloc-mod17.so = -Wl,--no-as-needed
+
+$(objpfx)tst-ldconfig-ld_so_conf-update.out: $(objpfx)tst-ldconfig-ld-mod.so
+$(objpfx)tst-ldconfig-ld_so_conf-update: $(libdl)

elf/tst-ldconfig-ld-mod.c

@@ -0,0 +1,8 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+void
+bar (void)
+{
+  printf ("Called DSO.\n");
+}

elf/tst-ldconfig-ld_so_conf-update.c

@@ -0,0 +1,115 @@
+/* Test ldconfig after /etc/ld.so.conf update and verify that a running process
+   observes changes to /etc/ld.so.cache.
+
+   Copyright (C) 2019 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; see the file COPYING.LIB.  If
+   not, see <https://www.gnu.org/licenses/>.  */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <errno.h>
+
+#include <support/capture_subprocess.h>
+#include <support/check.h>
+#include <support/support.h>
+#include <support/xdlfcn.h>
+#include <support/xstdio.h>
+#include <support/xunistd.h>
+
+
+#define DSO "libldconfig-ld-mod.so"
+#define DSO_DIR "/tmp/tst-ldconfig"
+#define CONF "/etc/ld.so.conf"
+
+
+static void
+run_ldconfig (void *x __attribute__((unused)))
+{
+  char *prog = xasprintf ("%s/ldconfig", support_install_rootsbindir);
+  char *args[] = { prog, NULL };
+
+  execv (args[0], args);
+  FAIL_EXIT1 ("execv: %m");
+}
+
+
+/* Create a new directory.
+   Copy a test shared object there.
+   Try to dlopen it by soname.  This should fail.
+   (Directory is not searched.)
+   Run ldconfig.
+   Try to dlopen it again.  It should still fail.
+   (Directory is still not searched.)
+   Add the directory to /etc/ld.so.conf.
+   Try to dlopen it again.  It should still fail.
+   (The loader does not read /etc/ld.so.conf, only /etc/ld.so.cache.)
+   Run ldconfig.
+   Try to dlopen it again.  This should finally succeed.  */
+static int
+do_test (void)
+{
+  struct support_capture_subprocess result;
+
+  /* Create the needed directories.  */
+  xmkdirp ("/var/cache/ldconfig", 0777);
+  xmkdirp (DSO_DIR, 0777);
+
+  /* Rename the DSO to start with "lib" because there's an undocumented
+     filter in ldconfig where it ignores any file that doesn't start with
+     "lib" (for regular shared libraries) or "ld-" (for ld-linux-*).  */
+  if (rename ("/usr/lib64/tst-ldconfig-ld-mod.so",
+              "/tmp/tst-ldconfig/libldconfig-ld-mod.so"))
+    FAIL_EXIT1 ("Renaming/moving the DSO failed: %m");
+
+
+  /* Open the DSO.  We expect this to fail - tst-ldconfig directory
+     is not searched.  */
+  TEST_VERIFY_EXIT (dlopen (DSO, RTLD_NOW | RTLD_GLOBAL) == NULL);
+
+  FILE *fp = xfopen (CONF, "a+");
+  if (!fp)
+    FAIL_EXIT1 ("creating /etc/ld.so.conf failed: %m");
+  xfclose (fp);
+
+  /* Run ldconfig.  */
+  result = support_capture_subprocess (run_ldconfig, NULL);
+  support_capture_subprocess_check (&result, "execv", 0, sc_allow_none);
+
+  /* Try to dlopen the same DSO again, we expect this to fail again.  */
+  TEST_VERIFY_EXIT (dlopen (DSO, RTLD_NOW | RTLD_GLOBAL) == NULL);
+
+  /* Add tst-ldconfig directory to /etc/ld.so.conf.  */
+  fp = xfopen (CONF, "w");
+  if (!(fwrite (DSO_DIR, 1, sizeof (DSO_DIR), fp)))
+    FAIL_EXIT1 ("updating /etc/ld.so.conf failed: %m");
+  xfclose (fp);
+
+  /* Try to dlopen the same DSO again, we expect this to still fail.  */
+  TEST_VERIFY_EXIT (dlopen (DSO, RTLD_NOW | RTLD_GLOBAL) == NULL);
+
+  /* Run ldconfig again.  */
+  result = support_capture_subprocess (run_ldconfig, NULL);
+  support_capture_subprocess_check (&result, "execv", 0, sc_allow_none);
+  support_capture_subprocess_free (&result);
+
+  /* Finally, we expect dlopen to pass now.  */
+  TEST_VERIFY_EXIT (dlopen (DSO, RTLD_NOW | RTLD_GLOBAL) != NULL);
+
+  return 0;
+}
+
+#include <support/test-driver.c>

elf/tst-ldconfig-ld_so_conf-update.root/tst-ldconfig-ld_so_conf-update.script

@@ -0,0 +1 @@
+cp $B/elf/tst-ldconfig-ld-mod.so $L/tst-ldconfig-ld-mod.so