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Date: Mon, 1 May 2017 11:26:37 +0000
From: "Agostino Sarubbo" <ago@...too.org>
To: "oss-security@...ts.openwall.com" <oss-security@...ts.openwall.com>
Subject: libsndfile: heap-based buffer overflow in flac_buffer_copy (flac.c)

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
==26966==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x621000001110 at pc 0x7fd12fe865e6 bp 0x7ffea55e99f0 sp 0x7ffea55e99e8
READ of size 4 at 0x621000001110 thread T0
    #0 0x7fd12fe865e5 in flac_buffer_copy /tmp/portage/media-libs/libsndfile-1.0.28/work/libsndfile-1.0.28/src/flac.c:267:41
    #1 0x7fd12fe86ef4 in flac_read_loop /tmp/portage/media-libs/libsndfile-1.0.28/work/libsndfile-1.0.28/src/flac.c:928:3
    #2 0x7fd12fe721fb in flac_read_flac2i /tmp/portage/media-libs/libsndfile-1.0.28/work/libsndfile-1.0.28/src/flac.c:979:13
    #3 0x7fd12fdca3a2 in sf_readf_int /tmp/portage/media-libs/libsndfile-1.0.28/work/libsndfile-1.0.28/src/sndfile.c:1835:10
    #4 0x514b5d in sfe_copy_data_int /tmp/portage/media-libs/libsndfile-1.0.28/work/libsndfile-1.0.28/programs/common.c:87:16
    #5 0x5138d1 in main /tmp/portage/media-libs/libsndfile-1.0.28/work/libsndfile-1.0.28/programs/sndfile-convert.c:340:3
    #6 0x7fd12ed6578f in __libc_start_main /tmp/portage/sys-libs/glibc-2.23-r3/work/glibc-2.23/csu/../csu/libc-start.c:289
    #7 0x419e18 in _init (/usr/bin/sndfile-convert+0x419e18)

0x621000001110 is located 0 bytes to the right of 4112-byte region [0x621000000100,0x621000001110)
allocated by thread T0 here:
    #0 0x4d94e8 in malloc /tmp/portage/sys-libs/compiler-rt-sanitizers-4.0.0/work/compiler-rt-4.0.0.src/lib/asan/asan_malloc_linux.cc:66
    #1 0x7fd12eb2d492 in safe_malloc_muladd2_ /tmp/portage/media-libs/flac-1.3.2-r1/work/flac-1.3.2/include/share/alloc.h:153
    #2 0x7fd12eb2d492 in allocate_output_ /tmp/portage/media-libs/flac-1.3.2-r1/work/flac-1.3.2/src/libFLAC/stream_decoder.c:1294
    #3 0x7fd12eb2d492 in read_frame_ /tmp/portage/media-libs/flac-1.3.2-r1/work/flac-1.3.2/src/libFLAC/stream_decoder.c:2035

SUMMARY: AddressSanitizer: heap-buffer-overflow /tmp/portage/media-libs/libsndfile-1.0.28/work/libsndfile-1.0.28/src/flac.c:267:41 in flac_buffer_copy
Shadow bytes around the buggy address:
  0x0c427fff81d0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c427fff81e0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c427fff81f0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c427fff8200: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c427fff8210: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
=>0x0c427fff8220: 00 00[fa]fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c427fff8230: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c427fff8240: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c427fff8250: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c427fff8260: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c427fff8270: 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
  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
==26966==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-2017-8363

Reproducer:
https://github.com/asarubbo/poc/blob/master/00266-libsndfile-heapoverflow-flac_buffer_copy

Timeline:
2017-04-12: 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-heap-based-buffer-overflow-in-flac_buffer_copy-flac-c/

--
Agostino Sarubbo
Gentoo Linux Developer


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