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| author | Maciej W. Rozycki <macro@mips.com> | 2018-06-29 17:10:43 +0100 |
|---|---|---|
| committer | Maciej W. Rozycki <macro@mips.com> | 2018-06-29 17:10:43 +0100 |
| commit | bac15a72fcf0ed143dd959604d9317c4bb94160a (patch) | |
| tree | ee1cf8e549a08a11e885efedf4a54ee58d2cf6d3 /elf/dl-lookup.c | |
| parent | e69d994a63afc2d367f286a2a7df28cbf710f0fe (diff) | |
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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 e7feec374c63 ("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.
Diffstat (limited to 'elf/dl-lookup.c')
| -rw-r--r-- | elf/dl-lookup.c | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/elf/dl-lookup.c b/elf/dl-lookup.c index 401bc87c90..68ecc6179f 100644 --- a/elf/dl-lookup.c +++ b/elf/dl-lookup.c @@ -76,6 +76,7 @@ check_match (const char *const undef_name, unsigned int stt = ELFW(ST_TYPE) (sym->st_info); assert (ELF_RTYPE_CLASS_PLT == 1); if (__glibc_unlikely ((sym->st_value == 0 /* No value. */ + && sym->st_shndx != SHN_ABS && stt != STT_TLS) || ELF_MACHINE_SYM_NO_MATCH (sym) || (type_class & (sym->st_shndx == SHN_UNDEF)))) |