libsndfile: global buffer overflow in i2les_array (pcm.c)

["Agostino Sarubbo" <ago () gentoo org>]

Description:
libsndfile is a C library for reading and writing files containing sampled sound.

The complete ASan output of the issue:

# sndfile-convert $FILE out.wav
==27948==ERROR: AddressSanitizer: global-buffer-overflow on address 0x0000013cd13c at pc 0x7f59caaaaace bp 
0x7ffcab360cf0 sp 0x7ffcab360ce8 
READ of size 4 at 0x0000013cd13c thread T0   
    #0 0x7f59caaaaacd in i2les_array /tmp/portage/media-libs/libsndfile-1.0.28/work/libsndfile-1.0.28/src/pcm.c:670:15  
    #1 0x7f59caaaaacd in pcm_write_i2les /tmp/portage/media-libs/libsndfile-1.0.28/work/libsndfile-1.0.28/src/pcm.c:1696
    #2 0x7f59ca7bf831 in sf_writef_int 
/tmp/portage/media-libs/libsndfile-1.0.28/work/libsndfile-1.0.28/src/sndfile.c:2342:10
    #3 0x514b70 in sfe_copy_data_int 
/tmp/portage/media-libs/libsndfile-1.0.28/work/libsndfile-1.0.28/programs/common.c:88:3 
    #4 0x5138d1 in main 
/tmp/portage/media-libs/libsndfile-1.0.28/work/libsndfile-1.0.28/programs/sndfile-convert.c:340:3    
    #5 0x7f59c974178f in __libc_start_main 
/tmp/portage/sys-libs/glibc-2.23-r3/work/glibc-2.23/csu/../csu/libc-start.c:289   
    #6 0x419e18 in _init (/usr/bin/sndfile-convert+0x419e18)

0x0000013cd13c is located 4092 bytes to the right of global variable 'data' defined in 
'/tmp/portage/media-libs/libsndfile-1.0.28/work/libsndfile-1.0.28/programs/common.c:80:14' 
(0x13c8140) of size 16384  
SUMMARY: AddressSanitizer: global-buffer-overflow 
/tmp/portage/media-libs/libsndfile-1.0.28/work/libsndfile-1.0.28/src/pcm.c:670:15 in i2les_array    
Shadow bytes around the buggy address:  
  0x0000802719d0: f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9
  0x0000802719e0: f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9
  0x0000802719f0: f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9
  0x000080271a00: f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9
  0x000080271a10: f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9
=>0x000080271a20: f9 f9 f9 f9 f9 f9 f9[f9]00 00 00 00 00 00 00 00
  0x000080271a30: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x000080271a40: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x000080271a50: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x000080271a60: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x000080271a70: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
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 
  Freed heap region:       fd 
  Stack left redzone:      f1 
  Stack mid redzone:       f2 
  Stack right redzone:     f3 
  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
==27948==ABORTING

Affected version:
1.0.28

Fixed version:
N/A

Commit fix:
https://github.com/erikd/libsndfile/commit/fd0484aba8e51d16af1e3a880f9b8b857b385eb3

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

CVE:
CVE-2017-8365

Reproducer:
https://github.com/asarubbo/poc/blob/master/00263-libsndfile-globaloverflow-i2les_array

Timeline:
2017-04-11: bug discovered and reported to upstream
2017-04-12: upstream released a patch
2017-04-29: blog post about the issue
2017-04-30: CVE assigned

Note:
This bug was found with American Fuzzy Lop.

Permalink:
https://blogs.gentoo.org/ago/2017/04/29/libsndfile-global-buffer-overflow-in-i2les_array-pcm-c/

--
Agostino Sarubbo
Gentoo Linux Developer