[PATCH] Report dlsym, dlvsym lookup errors using dlerror [BZ #19509]

[Florian Weimer <fweimer at redhat dot com>]

I'm not sure if this is the right fix.  I traced back the lack of error
reporting to the original addition of the RTLD_NEXT functionality.  I
don't know why it was omitted from it.

I could not find any callers of _dl_lookup_symbol_x which with skip_map
!= NULL and which are not related to RTLD_NEXT, so this change looks
pretty conservative to me.

Florian

2016-02-09  Florian Weimer  <fweimer@redhat.com>

	[BZ #19509]
	* elf/dl-lookup.c (_dl_lookup_symbol_x): Report error even if
	skip_map != NULL.
	* elf/bug19509.c: New file.
	* elf/Makefile (tests): Add bug19509.
	(bug19509): Link against libdl.

diff --git a/elf/Makefile b/elf/Makefile
index 63a5355..18baa23 100644
--- a/elf/Makefile
+++ b/elf/Makefile
@@ -149,7 +149,8 @@ tests += loadtest restest1 preloadtest loadfail multiload origtest resolvfail \
 	 tst-nodelete) \
 	 tst-initorder tst-initorder2 tst-relsort1 tst-null-argv \
 	 tst-ptrguard1 tst-tlsalign tst-tlsalign-extern tst-nodelete-opened \
-	 tst-nodelete2 tst-audit11 tst-audit12
+	 tst-nodelete2 tst-audit11 tst-audit12 \
+	 bug19509
 #	 reldep9
 ifeq ($(build-hardcoded-path-in-tests),yes)
 tests += tst-dlopen-aout
@@ -1252,3 +1253,5 @@ $(objpfx)tst-prelink-cmp.out: tst-prelink.exp \
 			      $(objpfx)tst-prelink-conflict.out
 	cmp $^ > $@; \
 	$(evaluate-test)
+
+$(objpfx)bug19509: $(libdl)
diff --git a/elf/bug19509.c b/elf/bug19509.c
new file mode 100644
index 0000000..e7ccf88
--- /dev/null
+++ b/elf/bug19509.c
@@ -0,0 +1,106 @@
+/* Test error reporting for dlsym, dlvsym failures.
+   Copyright (C) 2016 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
+   <http://www.gnu.org/licenses/>.  */
+
+#include <dlfcn.h>
+#include <gnu/lib-names.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+/* Used to disambiguate symbol names.  */
+static int counter;
+
+static void
+test_one (void *handle, const char *name, void *(func) (void *, const char *),
+          const char *suffix)
+{
+  ++counter;
+  char symbol[32];
+  snprintf (symbol, sizeof (symbol), "no_such_symbol_%d", counter);
+  char *expected_message;
+  if (asprintf (&expected_message, ": undefined symbol: %s%s",
+                symbol, suffix) < 0)
+    {
+      printf ("error: asprintf: %m\n");
+      abort ();
+    }
+
+  void *addr = func (handle, symbol);
+  if (addr != NULL)
+    {
+      printf ("error: %s: found symbol \"no_such_symbol\"\n", name);
+      abort ();
+    }
+  const char *message = dlerror ();
+  if (message == NULL)
+    {
+      printf ("error: %s: missing error message\n", name);
+      abort ();
+    }
+  const char *message_without_path = strchrnul (message, ':');
+  if (strcmp (message_without_path, expected_message) != 0)
+    {
+      printf ("error: %s: unexpected error message: %s\n", name, message);
+      abort ();
+    }
+  free (expected_message);
+}
+
+static void
+test_handles (const char *name, void *(func) (void *, const char *),
+              const char *suffix)
+{
+  test_one (RTLD_DEFAULT, name, func, suffix);
+  test_one (RTLD_NEXT, name, func, suffix);
+
+  void *handle = dlopen (LIBC_SO, RTLD_LAZY);
+  if (handle == NULL)
+    {
+      printf ("error: cannot dlopen %s: %s\n", LIBC_SO, dlerror ());
+      abort ();
+    }
+  test_one (handle, name, func, suffix);
+  dlclose (handle);
+}
+
+static void *
+dlvsym_no_such_version (void *handle, const char *name)
+{
+  return dlvsym (handle, name, "NO_SUCH_VERSION");
+}
+
+static void *
+dlvsym_glibc_private (void *handle, const char *name)
+{
+  return dlvsym (handle, name, "GLIBC_PRIVATE");
+}
+
+static int
+do_test (void)
+{
+  test_handles ("dlsym", dlsym, "");
+  test_handles ("dlvsym", dlvsym_no_such_version,
+                ", version NO_SUCH_VERSION");
+  test_handles ("dlvsym", dlvsym_glibc_private,
+                ", version GLIBC_PRIVATE");
+
+  return 0;
+}
+
+
+#define TEST_FUNCTION do_test ()
+#include "../test-skeleton.c"
diff --git a/elf/dl-lookup.c b/elf/dl-lookup.c
index f577759..6d299c1 100644
--- a/elf/dl-lookup.c
+++ b/elf/dl-lookup.c
@@ -858,7 +858,6 @@ _dl_lookup_symbol_x (const char *undef_name, struct link_map *undef_map,
   if (__glibc_unlikely (current_value.s == NULL))
     {
       if ((*ref == NULL || ELFW(ST_BIND) ((*ref)->st_info) != STB_WEAK)
-	  && skip_map == NULL
 	  && !(GLRO(dl_debug_mask) & DL_DEBUG_UNUSED))
 	{
 	  /* We could find no value for a strong reference.  */
-- 
2.4.3