glibc 2.5 <= reloc types to crash bug Oct 20 2013 10:50AM
geinblues gmail com
| XADV-2013002 glibc 2.5 <= reloc types to crash bug |

Vulnerable versions:
- glibc 2.5 <=
Not vulnerable versions:
- glibc 2.6 >=
Testbed: linux distro
Type: Local
Impact: crash
Vendor: https://www.gnu.org/software/libc
Author: x90c <geinblues *nospam* gmail dot com>
Site: x90c.org


[Unspecified reloc types bug]
'defaults:' label codes on If not defined RTLD_BOOTSTRAP, glibc 2.5
defined RTLD_BOOTSTRAP default. The elf_machine_rel() of the
vulnerable glibc 2.5 ld-2.5.so doesn't process 'defaults:' In
the symbol relocation time. It means the ELF object 4bytes
altered with unspecified reloc types to crash.
('defaults:' label process unspecified reloc types to
calc reloc addr)

The vulnerable function sets *reloc_addr_arg as 5rd argument
(to reloc addr). and calc reloc addr. The unspecified reloc types
passed Improper value(on elf binary) on reloc_addr. An elf binary
with altered unspecified reloc_types to crash. BUG!

The bug can be used for rootkit technique via altering the ELF object.


auto inline void
__attribute ((always_inline))
elf_machine_rel (struct link_map *map, const Elf32_Rel *reloc,
const Elf32_Sym *sym, const struct r_found_version *version,
void *const reloc_addr_arg)
// reloc_addr = reloc_addr_arg(5rd argument as relative jump)
Elf32_Addr *const reloc_addr = reloc_addr_arg;


switch (r_type)

case R_386_GLOB_DAT:
case R_386_JMP_SLOT:
// *reloc_addr(*relocation addr) = value(relative addr calculated at above codes.)
*reloc_addr = value;
// XXX BUG: 'defaults:' label not exists!

#endif /* !RTLD_BOOTSTRAP */

Altering reloc types on the ELF binary.

add 'defaults:' label on above relocation code

2012/09/04 - The bug Discovered.
2013/10/20 - Advisory released on full-disclosure, bugtraq, exploit-db.

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