[FFmpeg-devel] [PATCH] avformat/aacdec: fix demuxing of very small frames

James Almer jamrial at gmail.com
Fri Apr 26 01:04:01 EEST 2019


10 bytes (id3v2 header amount of bytes) were being read before any checks
were made on the bitstream. The result was that we were overreading into
the next frame if the current one was 8 or 9 bytes long.

Fixes tickets #7271 and #7869.

Signed-off-by: James Almer <jamrial at gmail.com>
---
 libavformat/aacdec.c | 34 +++++++++++++++++++++-------------
 1 file changed, 21 insertions(+), 13 deletions(-)

diff --git a/libavformat/aacdec.c b/libavformat/aacdec.c
index bd324a1420..8a5450880b 100644
--- a/libavformat/aacdec.c
+++ b/libavformat/aacdec.c
@@ -20,6 +20,7 @@
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
+#include "libavutil/avassert.h"
 #include "libavutil/intreadwrite.h"
 #include "avformat.h"
 #include "avio_internal.h"
@@ -154,17 +155,8 @@ static int adts_aac_read_packet(AVFormatContext *s, AVPacket *pkt)
 {
     int ret, fsize;
 
-    // Parse all the ID3 headers between frames
-    while (1) {
-        ret = av_get_packet(s->pb, pkt, FFMAX(ID3v2_HEADER_SIZE, ADTS_HEADER_SIZE));
-        if (ret >= ID3v2_HEADER_SIZE && ff_id3v2_match(pkt->data, ID3v2_DEFAULT_MAGIC)) {
-            if ((ret = handle_id3(s, pkt)) >= 0) {
-                continue;
-            }
-        }
-        break;
-    }
-
+retry:
+    ret = av_get_packet(s->pb, pkt, ADTS_HEADER_SIZE);
     if (ret < 0)
         return ret;
 
@@ -174,8 +166,24 @@ static int adts_aac_read_packet(AVFormatContext *s, AVPacket *pkt)
     }
 
     if ((AV_RB16(pkt->data) >> 4) != 0xfff) {
-        av_packet_unref(pkt);
-        return AVERROR_INVALIDDATA;
+        // Parse all the ID3 headers between frames
+        int append = ID3v2_HEADER_SIZE - ADTS_HEADER_SIZE;
+
+        av_assert2(append > 0);
+        ret = av_append_packet(s->pb, pkt, append);
+        if (ret != append) {
+            av_packet_unref(pkt);
+            return AVERROR(EIO);
+        }
+        if (!ff_id3v2_match(pkt->data, ID3v2_DEFAULT_MAGIC)) {
+            av_packet_unref(pkt);
+            return AVERROR_INVALIDDATA;
+        }
+        ret = handle_id3(s, pkt);
+        if (ret < 0)
+            return ret;
+
+        goto retry;
     }
 
     fsize = (AV_RB32(pkt->data + 3) >> 13) & 0x1FFF;
-- 
2.21.0



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