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elf: Include libc.so.6 as main program in dependency sort (bug 20972)

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_dl_map_object_deps always sorts the initially loaded object first
during dependency sorting.  This means it is relocated last in
dl_open_worker.  This results in crashes in IFUNC resolvers without
lazy bindings if libraries are preloaded that refer to IFUNCs in
libc.so.6: the resolvers are called when libc.so.6 has not been
relocated yet, so references to _rtld_global_ro etc. crash.

The fix is to check against the libc.so.6 link map recorded by the
__libc_early_init framework, and let it participate in the dependency
sort.

This fixes bug 20972.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>
This commit is contained in:
Florian Weimer 2020-12-11 17:30:03 +01:00
parent cb81264fd9
commit 9ffa50b26b
3 changed files with 43 additions and 2 deletions
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2
elf/Makefile
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@ -229,7 +229,7 @@ tests-internal += loadtest unload unload2 circleload1 \
tst-ptrguard1 tst-stackguard1 tst-libc_dlvsym \
tst-create_format1 tst-tls-surplus tst-dl-hwcaps_split
tests-container += tst-pldd tst-dlopen-tlsmodid-container \
tst-dlopen-self-container
tst-dlopen-self-container tst-preload-pthread-libc
test-srcs = tst-pathopt
selinux-enabled := $(shell cat /selinux/enforce 2> /dev/null)
ifneq ($(selinux-enabled),1)

7
elf/dl-deps.c
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@ -611,7 +611,12 @@ Filters not supported with LD_TRACE_PRELINKING"));
memcpy (l_initfini, map->l_searchlist.r_list,
nlist * sizeof (struct link_map *));
_dl_sort_maps (&l_initfini[1], nlist - 1, NULL, false);
/* If libc.so.6 is the main map, it participates in the sort, so
that the relocation order is correct regarding libc.so.6. */
if (l_initfini[0] == GL (dl_ns)[l_initfini[0]->l_ns].libc_map)
_dl_sort_maps (l_initfini, nlist, NULL, false);
else
_dl_sort_maps (&l_initfini[1], nlist - 1, NULL, false);
/* Terminate the list of dependencies. */
l_initfini[nlist] = NULL;

36
elf/tst-preload-pthread-libc.c Normal file
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@ -0,0 +1,36 @@
/* Test relocation ordering if the main executable is libc.so.6 (bug 20972).
Copyright (C) 2020 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 <gnu/lib-names.h>
#include <stdio.h>
#include <support/support.h>
#include <unistd.h>
int
main (void)
{
char *libc = xasprintf ("%s/%s", support_slibdir_prefix, LIBC_SO);
char *argv[] = { libc, NULL };
char *envp[] = { (char *) "LD_PRELOAD=" LIBPTHREAD_SO,
/* Relocation ordering matters most without lazy binding. */
(char *) "LD_BIND_NOW=1",
NULL };
execve (libc, argv, envp);
printf ("execve of %s failed: %m\n", libc);
return 1;
}