libav: stack-based buffer overflow in aac_sync (aac_parser.c)

Description:
Libav is an open source set of tools for audio and video processing.

A crafted file causes a stack-based buffer overflow. The ASan report may be confused because it mentions get_bits, but the issue is in aac_sync.
This issue was discovered the past year, I reported it to Luca Barbato privately and I didn’t follow the state.
Before I made the report, the bug was noticed by Janne Grunau because the fate test reported a failure, then he fixed it, but at that time there wasn’t stable release(s) that included the fix.

The complete ASan output:

~ # avconv -i $FILE -f null -
==20736==ERROR: AddressSanitizer: stack-buffer-overflow on address 0x7ffd3bd34f4a at pc 0x7f0805611189 bp 0x7ffd3bd34e20 sp 0x7ffd3bd34e18
READ of size 4 at 0x7ffd3bd34f4a thread T0
    #0 0x7f0805611188 in get_bits /var/tmp/portage/media-video/libav-11.3/work/libav-11.3/libavcodec/get_bits.h:244:5
    #1 0x7f0805611188 in avpriv_aac_parse_header /var/tmp/portage/media-video/libav-11.3/work/libav-11.3/libavcodec/aacadtsdec.c:58
    #2 0x7f080560f19e in aac_sync /var/tmp/portage/media-video/libav-11.3/work/libav-11.3/libavcodec/aac_parser.c:43:17
    #3 0x7f080560a87b in ff_aac_ac3_parse /var/tmp/portage/media-video/libav-11.3/work/libav-11.3/libavcodec/aac_ac3_parser.c:48:25
    #4 0x7f0806fcd8e6 in av_parser_parse2 /var/tmp/portage/media-video/libav-11.3/work/libav-11.3/libavcodec/parser.c:157:13
    #5 0x7f0808efd4dd in parse_packet /var/tmp/portage/media-video/libav-11.3/work/libav-11.3/libavformat/utils.c:794:15
    #6 0x7f0808edae64 in read_frame_internal /var/tmp/portage/media-video/libav-11.3/work/libav-11.3/libavformat/utils.c:960:24
    #7 0x7f0808ee8783 in avformat_find_stream_info /var/tmp/portage/media-video/libav-11.3/work/libav-11.3/libavformat/utils.c:2156:15
    #8 0x4f62f6 in open_input_file /var/tmp/portage/media-video/libav-11.3/work/libav-11.3/avconv_opt.c:726:11
    #9 0x4f474f in open_files /var/tmp/portage/media-video/libav-11.3/work/libav-11.3/avconv_opt.c:2127:15
    #10 0x4f3f62 in avconv_parse_options /var/tmp/portage/media-video/libav-11.3/work/libav-11.3/avconv_opt.c:2164:11
    #11 0x528727 in main /var/tmp/portage/media-video/libav-11.3/work/libav-11.3/avconv.c:2629:11
    #12 0x7f0803c83aa4 in __libc_start_main /var/tmp/portage/sys-libs/glibc-2.20-r2/work/glibc-2.20/csu/libc-start.c:289
    #13 0x43a5d6 in _start (/usr/bin/avconv+0x43a5d6)

Address 0x7ffd3bd34f4a is located in stack of thread T0 at offset 170 in frame
    #0 0x7f080560ee3f in aac_sync /var/tmp/portage/media-video/libav-11.3/work/libav-11.3/libavcodec/aac_parser.c:31

  This frame has 3 object(s):
    [32, 64) 'bits'
    [96, 116) 'hdr'
    [160, 168) 'tmp' 0x10002779e9e0: 00 00 04 f2 f2 f2 f2 f2 00[f3]f3 f3 00 00 00 00                                                                                                                                                                                                              
  0x10002779e9f0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00                                                                                                                                                                                                              
  0x10002779ea00: 00 00 00 00 00 00 00 00 00 00 00 00 f1 f1 f1 f1                                                                                                                                                                                                              
  0x10002779ea10: 00 f2 f2 f2 04 f2 04 f3 00 00 00 00 00 00 00 00                                                                                                                                                                                                              
  0x10002779ea20: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00                                                                                                                                                                                                              
  0x10002779ea30: f1 f1 f1 f1 00 f3 f3 f3 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                                                                                                                                                                                                                                                  
  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                                                                                                                                                                                                                                                  
==20736==ABORTING                                                                                                                                                                                                                                                              

Affected version:
11.3 (and maybe past versions)

Fixed version:
11.5

Commit fix:
https://git.libav.org/?p=libav.git;a=commit;h=fb1473080223a634b8ac2cca48a632d037a0a69d

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

CVE:
CVE-2016-7393

Timeline:
2015-07-27: bug discovered
2015-07-28: bug reported privately to upstream
2016-08-20: blog post about the issue
2016-09-10: CVE sssigned

Note:
This bug was found with American Fuzzy Lop.
This bug does not affect ffmpeg.
A same fix, was applied to another part of (similar) code in the ac3_parser.c file.

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libav: stack-based buffer overflow in aac_sync (aac_parser.c)

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