elf: Refuse to dlopen PIE objects [BZ #24323]

Another executable has already been mapped, so the dynamic linker
cannot perform relocations correctly for the second executable.

ChangeLog

@@ -1,3 +1,15 @@
+2019-06-18  Florian Weimer  <fweimer@redhat.com>
+
+	[BZ #24323]
+	* include/elf.h (DT_1_SUPPORTED_MASK): Include DF_1_PIE.
+	* elf/dl-load.c (_dl_map_object_from_fd): Check for DF_1_PIE and
+	fail when called from dlopen.
+	* elf/Makefile [have-fpie && build-shared] (tests): Add
+	tst-dlopen-pie.
+	(tst-dlopen-pie): Link with -ldl.
+	(tst-dlopen-pie.out): Add run-time dependency on tst-pie1.
+	* elf/tst-dlopen-pie.c (do_test): New file.
+
 2019-06-17  Rafal Luzynski  <digitalfreak@lingonborough.com>
 
 	[BZ #24614]

elf/Makefile

@@ -310,7 +310,7 @@ test-xfail-tst-protected1b = yes
 endif
 ifeq (yesyes,$(have-fpie)$(build-shared))
 modules-names += tst-piemod1
-tests += tst-pie1 tst-pie2
+tests += tst-pie1 tst-pie2 tst-dlopen-pie
 tests-pie += tst-pie1 tst-pie2
 ifeq (yes,$(have-protected-data))
 tests += vismain
@@ -1084,6 +1084,8 @@ CFLAGS-tst-pie2.c += $(pie-ccflag)
 
 $(objpfx)tst-piemod1.so: $(libsupport)
 $(objpfx)tst-pie1: $(objpfx)tst-piemod1.so
+$(objpfx)tst-dlopen-pie: $(libdl)
+$(objpfx)tst-dlopen-pie.out: $(objpfx)tst-pie1
 
 ifeq (yes,$(build-shared))
 # NB: Please keep cet-built-dso in sysdeps/x86/Makefile in sync with

elf/dl-load.c

@@ -1158,6 +1158,10 @@ _dl_map_object_from_fd (const char *name, const char *origname, int fd,
 	goto call_lose;
       }
 
+    /* dlopen of an executable is not valid because it is not possible
+       to perform proper relocations, handle static TLS, or run the
+       ELF constructors.  For PIE, the check needs the dynamic
+       section, so there is another check below.  */
     if (__glibc_unlikely (type != ET_DYN)
 	&& __glibc_unlikely ((mode & __RTLD_OPENEXEC) == 0))
       {
@@ -1194,9 +1198,11 @@ _dl_map_object_from_fd (const char *name, const char *origname, int fd,
   elf_get_dynamic_info (l, NULL);
 
   /* Make sure we are not dlopen'ing an object that has the
-     DF_1_NOOPEN flag set.  */
+     DF_1_NOOPEN flag set, or a PIE object.  */
-  if (__glibc_unlikely (l->l_flags_1 & DF_1_NOOPEN)
+  if ((__glibc_unlikely (l->l_flags_1 & DF_1_NOOPEN)
-      && (mode & __RTLD_DLOPEN))
+       && (mode & __RTLD_DLOPEN))
+      || (__glibc_unlikely (l->l_flags_1 & DF_1_PIE)
+	  && __glibc_unlikely ((mode & __RTLD_OPENEXEC) == 0)))
     {
       /* We are not supposed to load this object.  Free all resources.  */
       _dl_unmap_segments (l);
@@ -1207,7 +1213,11 @@ _dl_map_object_from_fd (const char *name, const char *origname, int fd,
       if (l->l_phdr_allocated)
 	free ((void *) l->l_phdr);
 
-      errstring = N_("shared object cannot be dlopen()ed");
+      if (l->l_flags_1 & DF_1_PIE)
+	errstring
+	  = N_("cannot dynamically load position-independent executable");
+      else
+	errstring = N_("shared object cannot be dlopen()ed");
       goto call_lose;
     }
 

elf/tst-dlopen-pie.c

@@ -0,0 +1,49 @@
+/* dlopen test for PIE objects.
+   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; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+/* This test attempts to open the (otherwise unrelated) PIE test
+   program elf/tst-pie1 and expects the attempt to fail.  */
+
+#include <dlfcn.h>
+#include <stddef.h>
+#include <string.h>
+#include <support/check.h>
+#include <support/support.h>
+
+static void
+test_mode (int mode)
+{
+  char *pie_path = xasprintf ("%s/elf/tst-pie1", support_objdir_root);
+  if (dlopen (pie_path, mode) != NULL)
+    FAIL_EXIT1 ("dlopen succeeded unexpectedly (%d)", mode);
+  const char *message = dlerror ();
+  const char *expected
+    = "cannot dynamically load position-independent executable";
+  if (strstr (message, expected) == NULL)
+    FAIL_EXIT1 ("unexpected error message (mode %d): %s", mode, message);
+}
+
+static int
+do_test (void)
+{
+  test_mode (RTLD_LAZY);
+  test_mode (RTLD_NOW);
+  return 0;
+}
+
+#include <support/test-driver.c>

include/elf.h

@@ -23,7 +23,7 @@
 # endif
 # define DT_1_SUPPORTED_MASK \
    (DF_1_NOW | DF_1_NODELETE | DF_1_INITFIRST | DF_1_NOOPEN \
-    | DF_1_ORIGIN | DF_1_NODEFLIB)
+    | DF_1_ORIGIN | DF_1_NODEFLIB | DF_1_PIE)
 
 #endif /* !_ISOMAC */
 #endif /* elf.h */