heap overflow in ffmpeg (base64.c:133)

[Youngseok Choi]

Hi, while running afl++ on ffmpeg,
I found heap overflow in ffmpeg.

How to reproduce:

% ./ffmpeg -i "data:/;;,doubleweend"

Stack Trace:

==19450==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x609000000407 at pc 0x55838811cade bp 0x7ffd42d3c400 sp 0x7ffd42d3c3f0
WRITE of size 1 at 0x609000000407 thread T0
    #0 0x55838811cadd in av_base64_decode libavutil/base64.c:133
    #1 0x558385eb5f9e in data_open libavformat/data_uri.c:79
    #2 0x5583859af0ef in ffurl_connect libavformat/avio.c:209
    #3 0x5583859b015c in ffurl_open_whitelist libavformat/avio.c:347
    #4 0x5583859ba239 in ffio_open_whitelist libavformat/aviobuf.c:1230
    #5 0x558385d0c9d0 in io_open_default libavformat/options.c:151
    #6 0x558385a061c4 in init_input libavformat/demux.c:174
    #7 0x558385a06c66 in avformat_open_input libavformat/demux.c:254
    #8 0x558384ef1532 in ifile_open fftools/ffmpeg_demux.c:1051
    #9 0x558384f372f4 in open_files fftools/ffmpeg_opt.c:1244
    #10 0x558384f37669 in ffmpeg_parse_options fftools/ffmpeg_opt.c:1283
    #11 0x558384f750df in main fftools/ffmpeg.c:4160
    #12 0x7fcc4980fc86 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21c86)
    #13 0x558384ee0499 in _start (/home/youngseok/latest-subjects/ffmpeg/ffmpeg+0x52f499)

Environment:

• OS: Ubuntu 18.04
• gcc: 7.5.0
• ffmpeg: version N-109968-gcc76e8340d (git-master)

Note that I built ffmpeg with address sanitizer.

./configure --extra-cflags="-fsanitize=address -g -O0" \
--extra-cxxflags="-fsanitize=address -g -O0" --extra-ldflags="-fsanitize=address -g -O0" \
--disable-optimizations --disable-stripping

[mkver]

Fixed in 2d216566f258badd07bc58de1e089b6e4175dc46.