[FFmpeg-devel] [PATCH] fftools/ffprobe: Loop over correct number of streams when flushing decoders

* [FFmpeg-devel] [PATCH] fftools/ffprobe: Loop over correct number of streams when flushing decoders
@ 2022-11-03 15:17 Derek Buitenhuis
  2022-11-06 11:23 ` Derek Buitenhuis
  0 siblings, 1 reply; 4+ messages in thread
From: Derek Buitenhuis @ 2022-11-03 15:17 UTC (permalink / raw)
  To: ffmpeg-devel

Some formats like FLV can dynamically add streams during packet reading.
FFprobe does check for this an reallocate the global stream info, but does
not reallocate InputFrame's streams and decoders when this happens, which,
as a result, could have caused flushing to occur on an out of bounds stream
index, since the flush loop iterates over fmt_ctx's nb_streams, an not
ifiles, despite using ifile's streams.

This fixes an out of bounds read and segfult.

Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>
---
Sample file: https://www.dropbox.com/s/ocu1ta6xzw8j6e7/dynamic_stream_segfault.flv?dl=0

Repro commands:

    1. ffprobe -select_streams 1 -read_intervals '%+#60' -show_frames dynamic_stream_segfault.flv
    2. ffprobe -select_streams 1 -show_frames dynamic_stream_segfault.flv
---
 fftools/ffprobe.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fftools/ffprobe.c b/fftools/ffprobe.c
index 9b7e82fd8c..99adf615ae 100644
--- a/fftools/ffprobe.c
+++ b/fftools/ffprobe.c
@@ -2893,7 +2893,7 @@ static int read_interval_packets(WriterContext *w, InputFile *ifile,
     }
     av_packet_unref(pkt);
     //Flush remaining frames that are cached in the decoder
-    for (i = 0; i < fmt_ctx->nb_streams; i++) {
+    for (i = 0; i < ifile->nb_streams; i++) {
         pkt->stream_index = i;
         if (do_read_frames) {
             while (process_frame(w, ifile, frame, pkt, &(int){1}) > 0);
-- 
2.37.2

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