hls: disallow opening nested files in child demuxers

libavformat/hls.c

@@ -494,6 +494,16 @@ static int save_avio_options(AVFormatContext *s)
     return ret;
 }
 
+static int nested_io_open(AVFormatContext *s, AVIOContext **pb, const char *url,
+                          int flags, AVDictionary **opts)
+{
+    av_log(s, AV_LOG_ERROR,
+           "A HLS playlist item '%s' referred to an external file '%s'. "
+           "Opening this file was forbidden for security reasons\n",
+           s->filename, url);
+    return AVERROR(EPERM);
+}
+
 static int hls_read_header(AVFormatContext *s)
 {
     HLSContext *c = s->priv_data;
@@ -579,6 +589,7 @@ static int hls_read_header(AVFormatContext *s)
             goto fail;
         }
         v->ctx->pb       = &v->pb;
+        v->ctx->io_open  = nested_io_open;
         v->stream_offset = stream_offset;
         ret = avformat_open_input(&v->ctx, v->segments[0]->url, in_fmt, NULL);
         if (ret < 0)