[FFmpeg-devel] segfault in af_afade.c::activate

[Mark Niebur]

I just checked out master and I see the fix you mentioned.  This does not completely fix acrossfade for me.  I also had to apply the following patch:
diff --git a/libavfilter/af_afade.c b/libavfilter/af_afade.c
index 195fb65..446aa0a 100644
--- a/libavfilter/af_afade.c
+++ b/libavfilter/af_afade.c
@@ -459,11 +459,11 @@ static int activate(AVFilterContext *ctx)
         } else if (ff_inlink_acknowledge_status(ctx->inputs[1], &status, &pts)) {
             ff_outlink_set_status(ctx->outputs[0], status, pts);
             return 0;
-        } else {
-            if (ff_outlink_frame_wanted(ctx->outputs[0]) && !in) {
+        } else if (!in) {
+            if (ff_outlink_frame_wanted(ctx->outputs[0])) {
                 ff_inlink_request_frame(ctx->inputs[1]);
-                return 0;
             }
+           return 0;
         }
         in->pts = s->pts;
         s->pts += av_rescale_q(in->nb_samples,

Thanks,
Mark

> On Oct 15, 2019, at 2:26 PM, Paul B Mahol <onemda at gmail.com> wrote:
> 
> On 10/15/19, Mark Niebur <mniebur at thuuz.com> wrote:
>> Hello,
>> I'm trying to debug an issue I'm seeing where the filter "acrossfade"
>> produces a segfault.  This seemingly only happens in docker containers, and
>> I am seeing it when running a rather large filter chain.  I'm trying to get
>> to the bottom of it, but it would be really helpful to understand the
>> context around how libavfilter fills the filter input fifos.  This is the
>> code where I'm seeing the segfault:
>> 449     AVFrame *in = NULL, *out, *cf[2] = { NULL };
>> ...
>> 474     if (ff_inlink_queued_samples(ctx->inputs[0]) > s->nb_samples) {
>> 475         // consume some samples - this is not a crossfade overlap
>> 486     } else if (ff_inlink_queued_samples(ctx->inputs[1]) >=
>> s->nb_samples) {
>> 487         if (s->overlap) {
>> 488             out = ff_get_audio_buffer(outlink, s->nb_samples);
>> 489             if (!out)
>> 490                 return AVERROR(ENOMEM);
>> 491             // NO CHECK IS DONE HERE THAT ENOUGH SAMPLES ARE PRESENT
>> 491             // In our case, there are 0 samples, so
>> ff_inlink_consume_samples returns early and does not set cf[0]
>> 492             ret = ff_inlink_consume_samples(ctx->inputs[0],
>> s->nb_samples, s->nb_samples, &cf[0]);
>> 493             if (ret < 0) {
>> 494                 av_frame_free(&out);
>> 495                 return ret;
>> 496             }
>> 497             // SEGFAULT HERE
>> 498             ret = ff_inlink_consume_samples(ctx->inputs[1],
>> s->nb_samples, s->nb_samples, &cf[1]);
>> 499             if (ret < 0) {
>> 500                 av_frame_free(&out);
>> 501                 return ret;
>> 502             }
>> 
>> How does avfilter add samples to an inlink?  Does it just fill it randomly
>> or will it fill input 0 completely and then move on to input 1, 2, 3?  Even
>> when I fix this segfault by ensuring that
>> ff_inlink_queued_samples(ctx->inputs[0]) == s->nb_samples, I will still get
>> additional segfaults in the acrossfade code where ff_inlink_consume_samples
>> returns 0 and does not set the frame pointer.
> 
> I think this was just reported and fixed very recently.
> 
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