[FFmpeg-devel] [PATCH v2 1/3] fftools/ffmpeg_filter: fix NULL pointer dereference

[Zhao Zhili]

> On Dec 19, 2023, at 18:32, Anton Khirnov <anton at khirnov.net> wrote:
> 
> Quoting Zhao Zhili (2023-12-19 16:37:01)
>> From: Zhao Zhili <zhilizhao at tencent.com>
>> 
>> In close_output(), a dummy frame is created with format NONE passed
>> to enc_open(), which doesn't prepare for it. The NULL pointer
>> dereference happened at
>> av_pix_fmt_desc_get(enc_ctx->pix_fmt)->comp[0].depth.
>> 
>> When fgt.graph is NULL, skip fg_output_frame() since there is
>> nothing to output.
>> 
>> frame #0: 0x0000005555bc34a4 ffmpeg_g`enc_open(opaque=0xb400007efe2db690, frame=0xb400007efe2d9f70) at ffmpeg_enc.c:235:44
>> frame #1: 0x0000005555bef250 ffmpeg_g`enc_open(sch=0xb400007dde2d4090, enc=0xb400007e4e2daad0, frame=0xb400007efe2d9f70) at ffmpeg_sched.c:1462:11
>> frame #2: 0x0000005555bee094 ffmpeg_g`send_to_enc(sch=0xb400007dde2d4090, enc=0xb400007e4e2daad0, frame=0xb400007efe2d9f70) at ffmpeg_sched.c:1571:19
>> frame #3: 0x0000005555bee01c ffmpeg_g`sch_filter_send(sch=0xb400007dde2d4090, fg_idx=0, out_idx=0, frame=0xb400007efe2d9f70) at ffmpeg_sched.c:2154:12
>> frame #4: 0x0000005555bcf124 ffmpeg_g`close_output(ofp=0xb400007e4e2d85b0, fgt=0x0000007d1790eb08) at ffmpeg_filter.c:2225:15
>> frame #5: 0x0000005555bcb000 ffmpeg_g`fg_output_frame(ofp=0xb400007e4e2d85b0, fgt=0x0000007d1790eb08, frame=0x0000000000000000) at ffmpeg_filter.c:2317:16
>> frame #6: 0x0000005555bc7e48 ffmpeg_g`filter_thread(arg=0xb400007eae2ce7a0) at ffmpeg_filter.c:2836:15
>> frame #7: 0x0000005555bee568 ffmpeg_g`task_wrapper(arg=0xb400007d8e2db478) at ffmpeg_sched.c:2200:21
>> ---
>> fftools/ffmpeg_filter.c | 7 ++-----
>> 1 file changed, 2 insertions(+), 5 deletions(-)
>> 
>> diff --git a/fftools/ffmpeg_filter.c b/fftools/ffmpeg_filter.c
>> index 9fc877b437..69a49a071e 100644
>> --- a/fftools/ffmpeg_filter.c
>> +++ b/fftools/ffmpeg_filter.c
>> @@ -2335,10 +2335,7 @@ static int fg_output_step(OutputFilterPriv *ofp, FilterGraphThread *fgt,
>> 
>>     ret = av_buffersink_get_frame_flags(filter, frame,
>>                                         AV_BUFFERSINK_FLAG_NO_REQUEST);
>> -    if (ret == AVERROR_EOF && !fgt->eof_out[ofp->index]) {
>> -        ret = fg_output_frame(ofp, fgt, NULL);
>> -        return (ret < 0) ? ret : 1;
> 
> Why are you removing this block?

I misread what you mean
> I see, then seems to me it'd be better to run the final loop in
> filter_thread() (the one calling fg_output_frame(, NULL)) only when
> fgt->graph is non-NULL. That should fix this issue as well.
These two flush operations can be combined into a single one, no?

> 
> -- 
> Anton Khirnov
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