Yy: > > >> 2021年12月3日 下午8:06，Yy <young_chel...@163.com> 写道： >> >> >> >>> 2021年12月3日 下午5:42，Andreas Rheinhardt <andreas.rheinha...@outlook.com >>> <mailto:andreas.rheinha...@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 <os...@tsinghua.edu.cn> >>>> Signed-off-by: Yu Yang <young_chel...@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. - Andreas _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".
