[FFmpeg-devel] [PATCH] libavformat/flacdec: Workaround for truncated metadata picture size

[Mattias Wadman]

lavf flacenc could previously write truncated metadata picture size if
the picture data did not fit in 24 bits. Detect this by truncting the
size found inside the picture block and if it matches the block size
use it and read rest of picture data.

flacenc was fixed in e447a4d112bcfee10126c54eb4481fa8712957c8
---
 libavformat/flac_picture.c | 23 +++++++++++++++++++++--
 1 file changed, 21 insertions(+), 2 deletions(-)

diff --git a/libavformat/flac_picture.c b/libavformat/flac_picture.c
index 81ddf80465..17be497f95 100644
--- a/libavformat/flac_picture.c
+++ b/libavformat/flac_picture.c
@@ -32,11 +32,12 @@ int ff_flac_parse_picture(AVFormatContext *s, uint8_t *buf, int buf_size)
     const CodecMime *mime = ff_id3v2_mime_tags;
     enum AVCodecID id = AV_CODEC_ID_NONE;
     AVBufferRef *data = NULL;
-    uint8_t mimetype[64], *desc = NULL;
+    uint8_t mimetype[64], *desc = NULL, *picturebuf = NULL;
     GetByteContext g;
     AVStream *st;
     int width, height, ret = 0;
-    unsigned int len, type;
+    unsigned int type;
+    uint32_t len, left, lendiff;
 
     if (buf_size < 34) {
         av_log(s, AV_LOG_ERROR, "Attached picture metadata block too short\n");
@@ -114,6 +115,23 @@ int ff_flac_parse_picture(AVFormatContext *s, uint8_t *buf, int buf_size)
 
     /* picture data */
     len = bytestream2_get_be32u(&g);
+
+    // Workaround lavf flacenc bug that allowed writing truncated metadata picture block size if
+    // picture size did not fit in 24 bits
+    left = bytestream2_get_bytes_left(&g);
+    if (len > left && (len & 0xffffff) == left) {
+        av_log(s, AV_LOG_INFO, "Correcting truncated metadata picture size from %d to %d\n", left, len);
+
+        picturebuf = av_malloc(len);
+        if (!picturebuf)
+            RETURN_ERROR(AVERROR(ENOMEM));
+        lendiff = len - left;
+        bytestream2_get_buffer(&g, picturebuf, left);
+        if (avio_read(s->pb, picturebuf+left, lendiff) < lendiff)
+            RETURN_ERROR(AVERROR_INVALIDDATA);
+        bytestream2_init(&g, picturebuf, len);
+    }
+
     if (len <= 0 || len > bytestream2_get_bytes_left(&g)) {
         av_log(s, AV_LOG_ERROR, "Attached picture metadata block too short\n");
         if (s->error_recognition & AV_EF_EXPLODE)
@@ -155,6 +173,7 @@ int ff_flac_parse_picture(AVFormatContext *s, uint8_t *buf, int buf_size)
 fail:
     av_buffer_unref(&data);
     av_freep(&desc);
+    av_freep(&picturebuf);
 
     return ret;
 }
-- 
2.18.0