[FFmpeg-devel] [PATCH 3/6] avformat/aviobuf: Don't use NULL as src for memcpy

[Andreas Rheinhardt <andreas.rheinhardt@outlook.com>]

This might happen in avio_write() if size == 0
when the direct codepath is taken. It is undefined behaviour
according to the spec although it happens to work in practice.
Fixes the webm-webvtt-remux FATE-test under UBSan.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
---
 libavformat/aviobuf.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/libavformat/aviobuf.c b/libavformat/aviobuf.c
index b20b1a611a..5b6a42d7f4 100644
--- a/libavformat/aviobuf.c
+++ b/libavformat/aviobuf.c
@@ -231,6 +231,8 @@ void ffio_fill(AVIOContext *s, int b, int64_t count)
 
 void avio_write(AVIOContext *s, const unsigned char *buf, int size)
 {
+    if (size <= 0)
+        return;
     if (s->direct && !s->update_checksum) {
         avio_flush(s);
         writeout(s, buf, size);
@@ -246,7 +248,7 @@ void avio_write(AVIOContext *s, const unsigned char *buf, int size)
 
         buf += len;
         size -= len;
-    }
+    } while (size > 0);
 }
 
 void avio_flush(AVIOContext *s)
-- 
2.34.1

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