libdwarf: heap-based buffer overflow in _dwarf_skim_forms (dwarf_macro5.c)

[Agostino Sarubbo <ago () gentoo org>]

If it is suitable for a CVE please assign one. Thanks.

Description:
libdwarf is a library to consume and produce DWARF debug information.

A fuzz on an updated version revealed a buffer overflow.

The complete ASan output:

# dwarfdump $FILE
==2437==ERROR: AddressSanitizer: heap-buffer-overflow on address 
0x62000000fe5b at pc 0x000000462c7c bp 0x7ffea0d4b690 sp 0x7ffea0d4ae40
READ of size 29 at 0x62000000fe5b thread T0
    #0 0x462c7b in __interceptor_strlen /var/tmp/portage/sys-devel/llvm-3.8.1-
r2/work/llvm-3.8.1.src/projects/compiler-rt/lib/asan/asan_interceptors.cc:581
    #1 0x5edea2 in _dwarf_skim_forms 
/tmp/dwarf-20161021/libdwarf/dwarf_macro5.c:185:17
    #2 0x5edea2 in _dwarf_get_macro_ops_count_internal 
/tmp/dwarf-20161021/libdwarf/dwarf_macro5.c:346
    #3 0x5eb886 in _dwarf_internal_macro_context_by_offset 
/tmp/dwarf-20161021/libdwarf/dwarf_macro5.c:1338:11
    #4 0x5eb886 in _dwarf_internal_macro_context 
/tmp/dwarf-20161021/libdwarf/dwarf_macro5.c:1201
    #5 0x5ed10e in dwarf_get_macro_context_by_offset 
/tmp/dwarf-20161021/libdwarf/dwarf_macro5.c:1467:11
    #6 0x54f7be in print_macros_5style_this_cu 
/tmp/dwarf-20161021/dwarfdump/print_macro.c:288:16
    #7 0x514d0f in print_one_die_section 
/tmp/dwarf-20161021/dwarfdump/print_die.c:869:21
    #8 0x512262 in print_infos 
/tmp/dwarf-20161021/dwarfdump/print_die.c:371:16
    #9 0x4faafa in process_one_file 
/tmp/dwarf-20161021/dwarfdump/dwarfdump.c:1371:9
    #10 0x4faafa in main /tmp/dwarf-20161021/dwarfdump/dwarfdump.c:654
    #11 0x7f74b22e761f in __libc_start_main /var/tmp/portage/sys-
libs/glibc-2.22-r4/work/glibc-2.22/csu/libc-start.c:289
    #12 0x419588 in _start (/usr/bin/dwarfdump-asan+0x419588)

0x62000000fe5b is located 0 bytes to the right of 3547-byte region 
[0x62000000f080,0x62000000fe5b)
allocated by thread T0 here:
    #0 0x4c0ad8 in malloc /var/tmp/portage/sys-devel/llvm-3.8.1-
r2/work/llvm-3.8.1.src/projects/compiler-rt/lib/asan/asan_malloc_linux.cc:52
    #1 0x7f74b33c1206 in __libelf_set_rawdata_wrlock /tmp/portage/dev-
libs/elfutils-0.166/work/elfutils-0.166/libelf/elf_getdata.c:318

SUMMARY: AddressSanitizer: heap-buffer-overflow /var/tmp/portage/sys-
devel/llvm-3.8.1-r2/work/llvm-3.8.1.src/projects/compiler-
rt/lib/asan/asan_interceptors.cc:581 in __interceptor_strlen
Shadow bytes around the buggy address:
  0x0c407fff9f70: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c407fff9f80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c407fff9f90: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c407fff9fa0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c407fff9fb0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
=>0x0c407fff9fc0: 00 00 00 00 00 00 00 00 00 00 00[03]fa fa fa fa
  0x0c407fff9fd0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c407fff9fe0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c407fff9ff0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c407fffa000: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c407fffa010: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
Shadow byte legend (one shadow byte represents 8 application bytes):
  Addressable:           00
  Partially addressable: 01 02 03 04 05 06 07 
  Heap left redzone:       fa
  Heap right redzone:      fb
  Freed heap region:       fd
  Stack left redzone:      f1
  Stack mid redzone:       f2
  Stack right redzone:     f3
  Stack partial redzone:   f4
  Stack after return:      f5
  Stack use after scope:   f8
  Global redzone:          f9
  Global init order:       f6
  Poisoned by user:        f7
  Container overflow:      fc
  Array cookie:            ac
  Intra object redzone:    bb
  ASan internal:           fe
  Left alloca redzone:     ca
  Right alloca redzone:    cb
==2437==ABORTING

Affected version:
20161021

Fixed version:
N/A

Commit fix:
https://sourceforge.net/p/libdwarf/code/ci/583f8834083b5ef834c497f5b47797e16101a9a6/

Credit:
This bug was discovered by Agostino Sarubbo of Gentoo.

CVE:
N/A

Reproducer:
https://github.com/asarubbo/poc/blob/master/00027-libdwarf-heapoverflow-_dwarf_skim_forms

Timeline:
2016-11-02: bug discovered and reported to upstream
2016-11-05: upstream released a patch
2016-11-07: blog post about the issue

Note:
This bug was found with American Fuzzy Lop.

Permalink:
https://blogs.gentoo.org/ago/2016/11/07/libdwarf-heap-based-buffer-overflow-in-_dwarf_skim_forms-dwarf_macro5-c