commit 2c75b545de6fe3c44138799c68217a94bc669a88

Author: Florian Weimer <fweimer@redhat.com>

Date:   Tue Jun 18 16:42:10 2019 +0200

    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.

diff --git a/elf/Makefile b/elf/Makefile

index 08e2f99..27a2fa8 100644

--- a/elf/Makefile

+++ b/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

diff --git a/elf/dl-load.c b/elf/dl-load.c

index 2bbef81..5abeb86 100644

--- a/elf/dl-load.c

+++ b/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.  */

-  if (__glibc_unlikely (l->l_flags_1 & DF_1_NOOPEN)

-      && (mode & __RTLD_DLOPEN))

+     DF_1_NOOPEN flag set, or a PIE object.  */

+  if ((__glibc_unlikely (l->l_flags_1 & DF_1_NOOPEN)

+       && (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;

     }

diff --git a/elf/tst-dlopen-pie.c b/elf/tst-dlopen-pie.c

new file mode 100644

index 0000000..6a41c73

--- /dev/null

+++ b/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>

diff --git a/include/elf.h b/include/elf.h

index ab76aaf..14ed67f 100644

--- a/include/elf.h

+++ b/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 */