Yu Yang:
> fftools/ffmpegc When `ost->last_frame` is NULL, 'SEGV' occurs when accessing
> its pts.
>
> libavutil/framec `ost->last_frame` may be set NULL by av_frame_alloc(). In
> this situation，
> av_frame_unref() and av_frame_free() do nothing. Frame is
> not released.
>
> ```c
> // in fftools/ffmpeg.c:1145
> 1145 static void do_video_out(OutputFile *of, ...)
>
> 1148 {
> ...
> // `ost->last_frame` is NULL.
> 1272 av_log(NULL, AV_LOG_VERBOSE,
> 1273 "*** dropping frame %d from stream %d at ts %"PRId64"\n",
> 1274 ost->frame_number, ost->st->index, ost->last_frame->pts);
> ...
> 1421 if (!ost->last_frame)
> // `ost->last_frame` may be set NULL here.
> 1422 ost->last_frame = av_frame_alloc();
> ...
>
> 1433 }
> ```
>
> coredump backtrace info:
> ==7192==ERROR: AddressSanitizer: SEGV on unknown address 0x000000000088 (pc
> 0x0000005e87e2 bp 0x7fff84f0ffb0 sp 0x7fff84f0f020 T0)
> ==7192==The signal is caused by a READ memory access.
> ==7192==Hint: address points to the zero page.
> #0 0x5e87e2 in do_video_out
> /home/r1/ffmpeg/ffmpeg-4.4.1/build/src/fftools/ffmpeg.c:1274:68
> #1 0x5df341 in reap_filters
> /home/r1/ffmpeg/ffmpeg-4.4.1/build/src/fftools/ffmpeg.c:1548:25
> #2 0x5d08b7 in transcode_from_filter
> /home/r1/ffmpeg/ffmpeg-4.4.1/build/src/fftools/ffmpeg.c:4644:15
> #3 0x59e557 in transcode_step
> /home/r1/ffmpeg/ffmpeg-4.4.1/build/src/fftools/ffmpeg.c:4729:20
> #4 0x593970 in transcode
> /home/r1/ffmpeg/ffmpeg-4.4.1/build/src/fftools/ffmpeg.c:4805:15
> #5 0x58f7a4 in main
> /home/r1/ffmpeg/ffmpeg-4.4.1/build/src/fftools/ffmpeg.c:5010:9
> #6 0x7f0fa9d900b2 in __libc_start_main
> /build/glibc-eX1tMB/glibc-2.31/csu/../csu/libc-start.c:308:16
> #7 0x42033d in _start (/home/r1/ffmpeg/ffmpeg_4.4.1+0x42033d)
>
> Reported-by: TOTE Robot <[email protected]>
> Signed-off-by: Yu Yang <[email protected]>
> ---
> fftools/ffmpeg.c | 7 ++++---
> libavutil/frame.c | 9 ++++-----
> 2 files changed, 8 insertions(+), 8 deletions(-)
>
> diff --git a/fftools/ffmpeg.c b/fftools/ffmpeg.c
> index cfb04d5eff..cade05f762 100644
> --- a/fftools/ffmpeg.c
> +++ b/fftools/ffmpeg.c
> @@ -1265,9 +1265,10 @@ static void do_video_out(OutputFile *of,
>
> if (nb0_frames == 0 && ost->last_dropped) {
> nb_frames_drop++;
> - av_log(NULL, AV_LOG_VERBOSE,
> - "*** dropping frame %d from stream %d at ts %"PRId64"\n",
> - ost->frame_number, ost->st->index, ost->last_frame->pts);
> + if (ost->last_frame)
> + av_log(NULL, AV_LOG_VERBOSE,
> + "*** dropping frame %d from stream %d at ts %"PRId64"\n",
> + ost->frame_number, ost->st->index, ost->last_frame->pts);
> }
> if (nb_frames > (nb0_frames && ost->last_dropped) + (nb_frames >
> nb0_frames)) {
> if (nb_frames > dts_error_threshold * 30) {
> diff --git a/libavutil/frame.c b/libavutil/frame.c
> index d4d3ad6988..9c866320a7 100644
> --- a/libavutil/frame.c
> +++ b/libavutil/frame.c
> @@ -111,11 +111,10 @@ AVFrame *av_frame_alloc(void)
>
> void av_frame_free(AVFrame **frame)
> {
> - if (!frame || !*frame)
> - return;
> -
> - av_frame_unref(*frame);
> - av_freep(frame);
> + if (*frame)
> + av_frame_unref(*frame);
> + if (frame)
> + av_freep(frame);
> }
>
> static int get_video_buffer(AVFrame *frame, int align)
>
This change to frame.c is also completely wrong; this frame should
probably not be constantly allocated and freed and the code at lines
1422-1428 should actually error out in case of allocation error.
- Andreas
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