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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
parent
e69d994a63
commit
bac15a72fc
14
ChangeLog
14
ChangeLog
@ -1,3 +1,17 @@
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2018-06-29 Maciej W. Rozycki <macro@mips.com>
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[BZ #23307]
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* elf/dl-lookup.c (check_match): Do not reject a symbol whose
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`st_value' is 0 if `st_shndx' is SHN_ABS.
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* elf/tst-absolute-zero.c: New file.
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* elf/tst-absolute-zero-lib.c: New file.
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* elf/tst-absolute-zero-lib.lds: New file.
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* elf/Makefile (tests): Add `tst-absolute-zero'.
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(modules-names): Add `tst-absolute-zero-lib'.
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(LDLIBS-tst-absolute-zero-lib.so): New variable.
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($(objpfx)tst-absolute-zero-lib.so): New dependency.
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($(objpfx)tst-absolute-zero: New dependency.
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2018-06-29 Zack Weinberg <zackw@panix.com>
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* configure.ac: New command-line option --disable-crypt.
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@ -186,7 +186,7 @@ tests += restest1 preloadtest loadfail multiload origtest resolvfail \
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tst-tlsalign tst-tlsalign-extern tst-nodelete-opened \
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tst-nodelete2 tst-audit11 tst-audit12 tst-dlsym-error tst-noload \
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tst-latepthread tst-tls-manydynamic tst-nodelete-dlclose \
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tst-debug1 tst-main1 tst-absolute-sym tst-big-note
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tst-debug1 tst-main1 tst-absolute-sym tst-absolute-zero tst-big-note
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# reldep9
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tests-internal += loadtest unload unload2 circleload1 \
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neededtest neededtest2 neededtest3 neededtest4 \
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@ -273,7 +273,7 @@ modules-names = testobj1 testobj2 testobj3 testobj4 testobj5 testobj6 \
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tst-latepthreadmod $(tst-tls-many-dynamic-modules) \
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tst-nodelete-dlclose-dso tst-nodelete-dlclose-plugin \
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tst-main1mod tst-libc_dlvsym-dso tst-absolute-sym-lib \
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tst-big-note-lib
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tst-absolute-zero-lib tst-big-note-lib
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ifeq (yes,$(have-mtls-dialect-gnu2))
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tests += tst-gnu2-tls1
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@ -1467,6 +1467,10 @@ LDLIBS-tst-absolute-sym-lib.so = tst-absolute-sym-lib.lds
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$(objpfx)tst-absolute-sym-lib.so: $(LDLIBS-tst-absolute-sym-lib.so)
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$(objpfx)tst-absolute-sym: $(objpfx)tst-absolute-sym-lib.so
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LDLIBS-tst-absolute-zero-lib.so = tst-absolute-zero-lib.lds
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$(objpfx)tst-absolute-zero-lib.so: $(LDLIBS-tst-absolute-zero-lib.so)
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$(objpfx)tst-absolute-zero: $(objpfx)tst-absolute-zero-lib.so
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# Both the main program and the DSO for tst-libc_dlvsym need to link
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# against libdl.
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$(objpfx)tst-libc_dlvsym: $(libdl)
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@ -76,6 +76,7 @@ check_match (const char *const undef_name,
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unsigned int stt = ELFW(ST_TYPE) (sym->st_info);
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assert (ELF_RTYPE_CLASS_PLT == 1);
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if (__glibc_unlikely ((sym->st_value == 0 /* No value. */
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&& sym->st_shndx != SHN_ABS
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&& stt != STT_TLS)
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|| ELF_MACHINE_SYM_NO_MATCH (sym)
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|| (type_class & (sym->st_shndx == SHN_UNDEF))))
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25
elf/tst-absolute-zero-lib.c
Normal file
25
elf/tst-absolute-zero-lib.c
Normal file
@ -0,0 +1,25 @@
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/* BZ #23307 absolute zero symbol calculation shared module.
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Copyright (C) 2018 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<http://www.gnu.org/licenses/>. */
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extern char absolute;
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void *
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get_absolute (void)
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{
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return &absolute;
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}
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1
elf/tst-absolute-zero-lib.lds
Normal file
1
elf/tst-absolute-zero-lib.lds
Normal file
@ -0,0 +1 @@
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"absolute" = 0;
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38
elf/tst-absolute-zero.c
Normal file
38
elf/tst-absolute-zero.c
Normal file
@ -0,0 +1,38 @@
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/* BZ #23307 absolute zero symbol calculation main executable.
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Copyright (C) 2018 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<http://www.gnu.org/licenses/>. */
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#include <support/check.h>
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#include <support/support.h>
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#include <support/test-driver.h>
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void *get_absolute (void);
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static int
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do_test (void)
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{
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void *ref = (void *) 0;
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void *ptr;
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ptr = get_absolute ();
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if (ptr != ref)
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FAIL_EXIT1 ("Got %p, expected %p\n", ptr, ref);
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return 0;
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}
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#include <support/test-driver.c>
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