elf: Accept absolute (SHN_ABS) symbols whose value is zero [BZ #23307]

We have this condition in `check_match' (in elf/dl-lookup.c):

  if (__glibc_unlikely ((sym->st_value == 0 /* No value.  */
                         && stt != STT_TLS)
                        || ELF_MACHINE_SYM_NO_MATCH (sym)
                        || (type_class & (sym->st_shndx == SHN_UNDEF))))
    return NULL;

which causes all !STT_TLS symbols whose value is zero to be silently
ignored in lookup.  This may make sense for regular symbols, however not
for absolute (SHN_ABS) ones, where zero is like any value, there's no
special meaning attached to it.

Consequently legitimate programs fail, for example taking the
`elf/tst-absolute-sym' test case, substituting 0 for 0x55aa in
`elf/tst-absolute-sym-lib.lds' and then trying to run the resulting
program we get this:

$ .../elf/tst-absolute-sym
.../elf/tst-absolute-sym: symbol lookup error: .../elf/tst-absolute-sym-lib.so: undefined symbol: absolute
$

even though the symbol clearly is there:

$ readelf --dyn-syms .../elf/tst-absolute-sym-lib.so | grep '\babsolute\b'
     7: 00000000     0 NOTYPE  GLOBAL DEFAULT  ABS absolute
$

The check for the zero value has been there since forever or commit
d66e34cd4234/08162fa88891 ("Implemented runtime dynamic linker to
support ELF shared libraries.") dating back to May 2nd 1995, and the
problem triggers regardless of commit e7feec374c ("elf: Correct
absolute (SHN_ABS) symbol run-time calculation [BZ #19818]") being
present or not.

Fix the issue then, by permitting `sym->st_value' to be 0 for SHN_ABS
symbols in lookup.

	[BZ #23307]
	* elf/dl-lookup.c (check_match): Do not reject a symbol whose
	`st_value' is 0 if `st_shndx' is SHN_ABS.
	* elf/tst-absolute-zero.c: New file.
	* elf/tst-absolute-zero-lib.c: New file.
	* elf/tst-absolute-zero-lib.lds: New file.
	* elf/Makefile (tests): Add `tst-absolute-zero'.
	(modules-names): Add `tst-absolute-zero-lib'.
	(LDLIBS-tst-absolute-zero-lib.so): New variable.
	($(objpfx)tst-absolute-zero-lib.so): New dependency.
	($(objpfx)tst-absolute-zero: New dependency.
This commit is contained in:
Maciej W. Rozycki 2018-06-29 17:10:43 +01:00
parent e69d994a63
commit bac15a72fc
6 changed files with 85 additions and 2 deletions

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@ -1,3 +1,17 @@
2018-06-29 Maciej W. Rozycki <macro@mips.com>
[BZ #23307]
* elf/dl-lookup.c (check_match): Do not reject a symbol whose
`st_value' is 0 if `st_shndx' is SHN_ABS.
* elf/tst-absolute-zero.c: New file.
* elf/tst-absolute-zero-lib.c: New file.
* elf/tst-absolute-zero-lib.lds: New file.
* elf/Makefile (tests): Add `tst-absolute-zero'.
(modules-names): Add `tst-absolute-zero-lib'.
(LDLIBS-tst-absolute-zero-lib.so): New variable.
($(objpfx)tst-absolute-zero-lib.so): New dependency.
($(objpfx)tst-absolute-zero: New dependency.
2018-06-29 Zack Weinberg <zackw@panix.com> 2018-06-29 Zack Weinberg <zackw@panix.com>
* configure.ac: New command-line option --disable-crypt. * configure.ac: New command-line option --disable-crypt.

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@ -186,7 +186,7 @@ tests += restest1 preloadtest loadfail multiload origtest resolvfail \
tst-tlsalign tst-tlsalign-extern tst-nodelete-opened \ tst-tlsalign tst-tlsalign-extern tst-nodelete-opened \
tst-nodelete2 tst-audit11 tst-audit12 tst-dlsym-error tst-noload \ tst-nodelete2 tst-audit11 tst-audit12 tst-dlsym-error tst-noload \
tst-latepthread tst-tls-manydynamic tst-nodelete-dlclose \ tst-latepthread tst-tls-manydynamic tst-nodelete-dlclose \
tst-debug1 tst-main1 tst-absolute-sym tst-big-note tst-debug1 tst-main1 tst-absolute-sym tst-absolute-zero tst-big-note
# reldep9 # reldep9
tests-internal += loadtest unload unload2 circleload1 \ tests-internal += loadtest unload unload2 circleload1 \
neededtest neededtest2 neededtest3 neededtest4 \ neededtest neededtest2 neededtest3 neededtest4 \
@ -273,7 +273,7 @@ modules-names = testobj1 testobj2 testobj3 testobj4 testobj5 testobj6 \
tst-latepthreadmod $(tst-tls-many-dynamic-modules) \ tst-latepthreadmod $(tst-tls-many-dynamic-modules) \
tst-nodelete-dlclose-dso tst-nodelete-dlclose-plugin \ tst-nodelete-dlclose-dso tst-nodelete-dlclose-plugin \
tst-main1mod tst-libc_dlvsym-dso tst-absolute-sym-lib \ tst-main1mod tst-libc_dlvsym-dso tst-absolute-sym-lib \
tst-big-note-lib tst-absolute-zero-lib tst-big-note-lib
ifeq (yes,$(have-mtls-dialect-gnu2)) ifeq (yes,$(have-mtls-dialect-gnu2))
tests += tst-gnu2-tls1 tests += tst-gnu2-tls1
@ -1467,6 +1467,10 @@ LDLIBS-tst-absolute-sym-lib.so = tst-absolute-sym-lib.lds
$(objpfx)tst-absolute-sym-lib.so: $(LDLIBS-tst-absolute-sym-lib.so) $(objpfx)tst-absolute-sym-lib.so: $(LDLIBS-tst-absolute-sym-lib.so)
$(objpfx)tst-absolute-sym: $(objpfx)tst-absolute-sym-lib.so $(objpfx)tst-absolute-sym: $(objpfx)tst-absolute-sym-lib.so
LDLIBS-tst-absolute-zero-lib.so = tst-absolute-zero-lib.lds
$(objpfx)tst-absolute-zero-lib.so: $(LDLIBS-tst-absolute-zero-lib.so)
$(objpfx)tst-absolute-zero: $(objpfx)tst-absolute-zero-lib.so
# Both the main program and the DSO for tst-libc_dlvsym need to link # Both the main program and the DSO for tst-libc_dlvsym need to link
# against libdl. # against libdl.
$(objpfx)tst-libc_dlvsym: $(libdl) $(objpfx)tst-libc_dlvsym: $(libdl)

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@ -76,6 +76,7 @@ check_match (const char *const undef_name,
unsigned int stt = ELFW(ST_TYPE) (sym->st_info); unsigned int stt = ELFW(ST_TYPE) (sym->st_info);
assert (ELF_RTYPE_CLASS_PLT == 1); assert (ELF_RTYPE_CLASS_PLT == 1);
if (__glibc_unlikely ((sym->st_value == 0 /* No value. */ if (__glibc_unlikely ((sym->st_value == 0 /* No value. */
&& sym->st_shndx != SHN_ABS
&& stt != STT_TLS) && stt != STT_TLS)
|| ELF_MACHINE_SYM_NO_MATCH (sym) || ELF_MACHINE_SYM_NO_MATCH (sym)
|| (type_class & (sym->st_shndx == SHN_UNDEF)))) || (type_class & (sym->st_shndx == SHN_UNDEF))))

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@ -0,0 +1,25 @@
/* BZ #23307 absolute zero symbol calculation shared module.
Copyright (C) 2018 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/>. */
extern char absolute;
void *
get_absolute (void)
{
return &absolute;
}

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@ -0,0 +1 @@
"absolute" = 0;

38
elf/tst-absolute-zero.c Normal file
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@ -0,0 +1,38 @@
/* BZ #23307 absolute zero symbol calculation main executable.
Copyright (C) 2018 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 <support/check.h>
#include <support/support.h>
#include <support/test-driver.h>
void *get_absolute (void);
static int
do_test (void)
{
void *ref = (void *) 0;
void *ptr;
ptr = get_absolute ();
if (ptr != ref)
FAIL_EXIT1 ("Got %p, expected %p\n", ptr, ref);
return 0;
}
#include <support/test-driver.c>