avcodec/avcodec: Limit the number of side data elements per packet

Fixes: 1293/clusterfuzz-testcase-minimized-6054752074858496

See: [FFmpeg-devel] [PATCH] avcodec/avcodec: Limit the number of side data elements per packet

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/targets/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit d5711cb891)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/avcodec.h

@@ -1583,6 +1583,16 @@ enum AVPacketSideDataType {
      * to the AVSphericalMapping structure.
      */
     AV_PKT_DATA_SPHERICAL,
+
+    /**
+     * The number of side data elements (in fact a bit more than it).
+     * This is not part of the public API/ABI in the sense that it may
+     * change when new side data types are added.
+     * This must stay the last enum value.
+     * If its value becomes huge, some code using it
+     * needs to be updated as it assumes it to be smaller than other limits.
+     */
+    AV_PKT_DATA_NB
 };
 
 #define AV_PKT_DATA_QUALITY_FACTOR AV_PKT_DATA_QUALITY_STATS //DEPRECATED

libavcodec/avpacket.c

@@ -298,7 +298,7 @@ int av_packet_add_side_data(AVPacket *pkt, enum AVPacketSideDataType type,
     AVPacketSideData *tmp;
     int elems = pkt->side_data_elems;
 
-    if ((unsigned)elems + 1 > INT_MAX / sizeof(*pkt->side_data))
+    if ((unsigned)elems + 1 > AV_PKT_DATA_NB)
         return AVERROR(ERANGE);
 
     tmp = av_realloc(pkt->side_data, (elems + 1) * sizeof(*tmp));
@@ -436,6 +436,9 @@ int av_packet_split_side_data(AVPacket *pkt){
             p-= size+5;
         }
 
+        if (i > AV_PKT_DATA_NB)
+            return AVERROR(ERANGE);
+
         pkt->side_data = av_malloc_array(i, sizeof(*pkt->side_data));
         if (!pkt->side_data)
             return AVERROR(ENOMEM);