In most cases, flv_read_metabody reads pass the beginning of the meta_pos.
if the beginning of the meta_pos had been flushed from the IO buffer,
we would not be able to seek to the right position (for a nonseekable stream).

Is better to check the seek result and skip the current flv body if necessary, than to silently try to read from a
desynchronized stream that will only be interpreted as garbage.

Signed-off-by: Armstrong Huang <armstr...@sweelia.com>
---
 libavformat/flvdec.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/libavformat/flvdec.c b/libavformat/flvdec.c
index d83edff727..9d2b0730f1 100644
--- a/libavformat/flvdec.c
+++ b/libavformat/flvdec.c
@@ -1096,7 +1096,14 @@ retry:
             } else if (type == TYPE_UNKNOWN) {
                 stream_type = FLV_STREAM_TYPE_DATA;
             }
-            avio_seek(s->pb, meta_pos, SEEK_SET);
+            if (avio_seek(s->pb, meta_pos, SEEK_SET) != meta_pos) {
+                // This can happen after flv_read_metabody
+                // above, on a non-seekable input, and the
+                // preceding data has been flushed out from
+                // the IO buffer.
+ av_log(s, AV_LOG_ERROR, "Unable to seek back to the flv tag body\n");
+                goto skip;
+            }
         }
     } else {
         av_log(s, AV_LOG_DEBUG,
--
2.20.1

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