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

[Yy]

> 2021年12月3日 下午5:42，Andreas Rheinhardt <andreas.rheinhardt at outlook.com> 写道：
> 
> 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).
Thanks for your advice, i will try to fix it again.
> 
> - Andreas
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