[FFmpeg-devel] fftools/ffmpeg_optc AVDictionary **opts, If memory allocation fails,

[Andreas Rheinhardt]

Yu Yang:
> Opts is assigned by setup_find_stream_info_opts(). Opts may be NULL.
> This situation is compatible in avformat_find_stream_info(). 
> Before av_dict_free(), the necessary checks were ignored.
> 
> // in fftools/ffmpeg_opt.c:1266
> 1067 static int open_input_file(OptionsContext *o, const char *filename)
> 1068 {
>       ...
> 1191         AVDictionary **opts = setup_find_stream_info_opts(ic, o->g->codec_opts);
>       ...
> 1196         ret = avformat_find_stream_info(ic, opts);
> 1197 
> 1198         for (i = 0; i < orig_nb_streams; i++)
> 1199             av_dict_free(&opts[i]);
>       ...
> 1342 }
> ```
> ```c
> // in libavutil/dict.c:203
> 203 void av_dict_free(AVDictionary **pm)
> 204 {
> 205     AVDictionary *m = *pm;
>       ...
> 215 }
> 
> coredump backtrace info:
> ==6235==ERROR: AddressSanitizer: SEGV on unknown address 0x000000000000 (pc 0x000006ba9c2f bp 0x7ffc3d5baa30 sp 0x7ffc3d5ba9a0 T0)
> ==6235==The signal is caused by a READ memory access.
> ==6235==Hint: address points to the zero page.
>     #0 0x6ba9c2f in av_dict_free /home/r1/ffmpeg/ffmpeg-4.4.1/build/src/libavutil/dict.c:205:23
>     #1 0x4ce5ac in open_input_file /home/r1/ffmpeg/ffmpeg-4.4.1/build/src/fftools/ffmpeg_opt.c:1199:13
>     #2 0x4c9dc0 in open_files /home/r1/ffmpeg/ffmpeg-4.4.1/build/src/fftools/ffmpeg_opt.c:3338:15
>     #3 0x4c9295 in ffmpeg_parse_options /home/r1/ffmpeg/ffmpeg-4.4.1/build/src/fftools/ffmpeg_opt.c:3378:11
>     #4 0x58f241 in main /home/r1/ffmpeg/ffmpeg-4.4.1/build/src/fftools/ffmpeg.c:4988:11
>     #5 0x7fe35197f0b2 in __libc_start_main /build/glibc-eX1tMB/glibc-2.31/csu/../csu/libc-start.c:308:16
>     #6 0x42033d in _start (/home/r1/ffmpeg/ffmpeg_4.4.1+0x42033d)
> 
> Reported-by: TOTE Robot <oslab at tsinghua.edu.cn>
> Signed-off-by: Yu Yang <young_chelsea at 163.com>
> ---
>  fftools/ffmpeg_opt.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/fftools/ffmpeg_opt.c b/fftools/ffmpeg_opt.c
> index a27263b879..a9fc54d948 100644
> --- a/fftools/ffmpeg_opt.c
> +++ b/fftools/ffmpeg_opt.c
> @@ -1197,10 +1197,11 @@ static int open_input_file(OptionsContext *o, const char *filename)
>          /* If not enough info to get the stream parameters, we decode the
>             first frames to get it. (used in mpeg case for example) */
>          ret = avformat_find_stream_info(ic, opts);
> -
> -        for (i = 0; i < orig_nb_streams; i++)
> -            av_dict_free(&opts[i]);
> -        av_freep(&opts);
> +        if (opts){
> +            for (i = 0; i < orig_nb_streams; i++)
> +                av_dict_free(&opts[i]);
> +            av_freep(&opts);
> +        }
>  
>          if (ret < 0) {
>              av_log(NULL, AV_LOG_FATAL, "%s: could not find codec parameters\n", filename);
> 

You should instead check setup_find_stream_info_opts() (either only call
it if orig_nb_streams is > 0 or modify it to return an error code given
that it can currently return NULL even on nonerror).

- Andreas