Re: [FFmpeg-devel] [PATCH 1/2] fftools/ffmpeg_filter: fix null pointer dereference

[Zhao Zhili <quinkblack@foxmail.com>]

> On Dec 18, 2023, at 19:19, Anton Khirnov <anton@khirnov.net> wrote:
> 
> Quoting Zhao Zhili (2023-12-17 12:01:08)
>> From: Zhao Zhili <zhilizhao@tencent.com>
>> 
>> 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.
>> 
>> 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
>> 
>> Signed-off-by: Zhao Zhili <zhilizhao@tencent.com>
>> ---
>> This bug is trigged by 10bit H.264 which doesn't supported by mediacodec.
>> There is some misleading error messages from ffmpeg cli:
>> 
>> [h264_mediacodec @ 0xb400007513788010] Failed to dequeue output buffer (status=-10000)
>> [vist#0:0/h264 @ 0xb4000074a3786b30] Error submitting packet to decoder: Generic error in an external library
>> [h264_mediacodec @ 0xb400007513788010] Failed to dequeue output buffer (status=-10000)
>> [vist#0:0/h264 @ 0xb4000074a3786b30] Error submitting packet to decoder: Generic error in an external library
>> [vist#0:0/h264 @ 0xb4000074a3786b30] A decoder returned an unexpected error code. This is a bug, please report it.
>> [vist#0:0/h264 @ 0xb4000074a3786b30] Error processing packet in decoder: Internal bug, should not have happened
>> 
>> fftools/ffmpeg_filter.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>> 
>> diff --git a/fftools/ffmpeg_filter.c b/fftools/ffmpeg_filter.c
>> index bb755d7bb4..9dc47f9d90 100644
>> --- a/fftools/ffmpeg_filter.c
>> +++ b/fftools/ffmpeg_filter.c
>> @@ -2192,7 +2192,7 @@ static int close_output(OutputFilterPriv *ofp, FilterGraphThread *fgt)
>> 
>>     // we are finished and no frames were ever seen at this output,
>>     // at least initialize the encoder with a dummy frame
>> -    if (!fgt->got_frame) {
>> +    if (!fgt->got_frame && ofp->format != -1) {
> 
> I don't quite understand how precisely does this happen.
> 
> This code should only be reachable if the filtergraph was configured at
> least once, then configure_filtergraph() should set ofp->format to the
> format reported by the lavfi buffersink. Does this then mean that lavfi
> is configured with AV_PIX_FMT_NONE? Or that this is somehow triggered
> without the filtergraph being configured?


Can reproduced with:

diff --git a/libavcodec/qsvdec.c b/libavcodec/qsvdec.c
index 559f63698a..af4ea37812 100644
--- a/libavcodec/qsvdec.c
+++ b/libavcodec/qsvdec.c
@@ -1050,6 +1050,7 @@ static int qsv_decode_frame(AVCodecContext *avctx, AVFrame *frame,
     QSVDecContext *s = avctx->priv_data;
     int ret;
 
+    return AVERROR_EXTERNAL;
     /* buffer the input packet */
     if (avpkt->size) {
         AVPacket input_ref;

Then
./ffmpeg -c:v h264_qsv -xerror  -I input.mp4 -c:a copy  -c:v libx264  output.mp4 

Looks like filtergraph isn’t being configured.

> 
> -- 
> Anton Khirnov
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