[FFmpeg-devel] [PATCH v1] libavcodec/flac_parser: Validate subframe zero bit and type

[Michael Niedermayer]

On Wed, Oct 13, 2021 at 06:15:26PM +0200, Mattias Wadman wrote:
> Reduces the risk of finding false frames that happens to have valid values and CRC.
> 
> Fixes ticket #9185 ffmpeg flac decoder incorrectly finds junk frame
> https://trac.ffmpeg.org/ticket/9185
> ---
>  libavcodec/flac_parser.c | 30 ++++++++++++++++++++++++++++--
>  1 file changed, 28 insertions(+), 2 deletions(-)

After this was applied out of array accesses appeared

tools/target_dem_flac_fuzzer: Running 1 inputs 1 time(s) each.
Running: libfuzz-repro/40109/clusterfuzz-testcase-minimized-ffmpeg_dem_FLAC_fuzzer-4805686811295744
=================================================================
==30399==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x633000052800 at pc 0x000001734048 bp 0x7ffd3598d090 sp 0x7ffd3598d088
READ of size 4 at 0x633000052800 thread T0
    #0 0x1734047 in get_bits libavcodec/get_bits.h:404:5
    #1 0x1734047 in frame_header_is_valid libavcodec/flac_parser.c:118
    #2 0x173ac77 in find_headers_search_validate libavcodec/flac_parser.c:202:9
    #3 0x173a851 in find_headers_search libavcodec/flac_parser.c:248:31
    #4 0x172f29b in find_new_headers libavcodec/flac_parser.c:268:18
    #5 0x172f29b in flac_parse libavcodec/flac_parser.c:666
    #6 0x13fb138 in av_parser_parse2 libavcodec/parser.c:165:13
    #7 0x6f1dba in parse_packet libavformat/demux.c:1127:15
    #8 0x6befe7 in read_frame_internal libavformat/demux.c:1322:24
    #9 0x6bafca in av_read_frame libavformat/demux.c:1426:17
    #10 0x4c7832 in LLVMFuzzerTestOneInput tools/target_dem_fuzzer.c:197:15
    #11 0x27055bd in fuzzer::Fuzzer::ExecuteCallback(unsigned char const*, unsigned long) Fuzzer/build/../FuzzerLoop.cpp:495:13
    #12 0x26fa192 in fuzzer::RunOneTest(fuzzer::Fuzzer*, char const*, unsigned long) Fuzzer/build/../FuzzerDriver.cpp:273:6
    #13 0x26ff391 in fuzzer::FuzzerDriver(int*, char***, int (*)(unsigned char const*, unsigned long)) Fuzzer/build/../FuzzerDriver.cpp:690:9
    #14 0x26f9e70 in main Fuzzer/build/../FuzzerMain.cpp:20:10
    #15 0x7f5d338b8bf6 in __libc_start_main /build/glibc-S9d2JN/glibc-2.27/csu/../csu/libc-start.c:310
    #16 0x41fb79 in _start (tools/target_dem_flac_fuzzer+0x41fb79)

0x633000052800 is located 0 bytes to the right of 106496-byte region [0x633000038800,0x633000052800)
allocated by thread T0 here:
    #0 0x498597 in posix_memalign /b/swarming/w/ir/cache/builder/src/third_party/llvm/compiler-rt/lib/asan/asan_malloc_linux.cc:226:3
    #1 0x26112c8 in av_malloc libavutil/mem.c:104:9
    #2 0x25a67b3 in av_fifo_alloc_array libavutil/fifo.c:51:20
    #3 0x172c9b6 in flac_parse_init libavcodec/flac_parser.c:747:21
    #4 0x13f7d67 in av_parser_init libavcodec/parser.c:67:15
    #5 0x6ce0b8 in avformat_find_stream_info libavformat/demux.c:2453:27
    #6 0x4c77d0 in LLVMFuzzerTestOneInput tools/target_dem_fuzzer.c:192:11
    #7 0x27055bd in fuzzer::Fuzzer::ExecuteCallback(unsigned char const*, unsigned long) Fuzzer/build/../FuzzerLoop.cpp:495:13
    #8 0x26fa192 in fuzzer::RunOneTest(fuzzer::Fuzzer*, char const*, unsigned long) Fuzzer/build/../FuzzerDriver.cpp:273:6
    #9 0x26ff391 in fuzzer::FuzzerDriver(int*, char***, int (*)(unsigned char const*, unsigned long)) Fuzzer/build/../FuzzerDriver.cpp:690:9
    #10 0x26f9e70 in main Fuzzer/build/../FuzzerMain.cpp:20:10
    #11 0x7f5d338b8bf6 in __libc_start_main /build/glibc-S9d2JN/glibc-2.27/csu/../csu/libc-start.c:310

SUMMARY: AddressSanitizer: heap-buffer-overflow libavcodec/get_bits.h:404:5 in get_bits
Shadow bytes around the buggy address:
  0x0c66800024b0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c66800024c0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c66800024d0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c66800024e0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c66800024f0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
=>0x0c6680002500:[fa]fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c6680002510: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c6680002520: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c6680002530: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c6680002540: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c6680002550: 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
  Shadow gap:              cc
==30399==ABORTING

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

The misfortune of the wise is better than the prosperity of the fool.
-- Epicurus
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 195 bytes
Desc: not available
URL: <https://ffmpeg.org/pipermail/ffmpeg-devel/attachments/20211020/4070cec8/attachment.sig>