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

[Yy]

> 2021年12月7日 上午1:48，Andreas Rheinhardt <andreas.rheinhardt at outlook.com> 写道：
> 
> Yy:
>> 
>> 
>>> 2021年12月3日 下午8:06，Yy <young_chelsea at 163.com> 写道：
>>> 
>>> 
>>> 
>>>> 2021年12月3日 下午5:42，Andreas Rheinhardt <andreas.rheinhardt at outlook.com <mailto: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
>> Hi, I try to fix this problem lastday and it not work. Today, I refer to your suggestion 
>> above to modify. But I think may be you misunderstood this bug. Because of no alloc memory for stream opts, ‘&opts[I]’ free caused crash.  And if orig_nb_streams == 0, 
>> crash won’t happen. So I think it is unnecessary to fix it call setup_find_stream_info_opts()
>> If orig_nb_streams is > 0. Opts == NULL when  orig_nb_streams == 0 or no alloc memory. 
>> I don’t think it is error. Because avformat_find_stream_info() allow opts == NULL. 
>> But we need to check if opts == NULL before releasing. May be this fix is right?
>> How do you think?   
>> Thx.
>> -Yu Yang
> 
> We don't need to check for opts == NULL before releasing if we actually
> checked that this array has been properly allocated in case it needs to
> be allocated; in case it could not be allocated, we should not call
> avformat_find_stream_info() at all.
I got it now. You mean it is redundant to check opts twice. It should 
return error when it could not be allocated at first time.  I will resubmit a 
new patch today. 
Thanks for your answer.  : )  
> 
> - Andreas
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