[FFmpeg-devel] [PATCH 3/3] avformat/mxfdec: Reduce overflows in essence_length computation

[Michael Niedermayer]

Fixes: signed integer overflow: -3741319169 - 9223372036823449370 cannot be represented in type 'long'
Fixes: 51896/clusterfuzz-testcase-minimized-ffmpeg_dem_MXF_fuzzer-513039428681728

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
---
 libavformat/mxfdec.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/libavformat/mxfdec.c b/libavformat/mxfdec.c
index e6118e141d..42109cb43a 100644
--- a/libavformat/mxfdec.c
+++ b/libavformat/mxfdec.c
@@ -100,7 +100,7 @@ typedef struct MXFPartition {
     uint64_t previous_partition;
     int index_sid;
     int body_sid;
-    int64_t this_partition;
+    uint64_t this_partition;
     int64_t essence_offset;         ///< absolute offset of essence
     int64_t essence_length;
     int32_t kag_size;
@@ -3519,8 +3519,12 @@ static void mxf_compute_essence_containers(AVFormatContext *s)
             p->essence_offset = p->first_essence_klv.offset;
 
             /* essence container spans to the next partition */
-            if (x < mxf->partitions_count - 1)
-                p->essence_length = mxf->partitions[x+1].this_partition - p->essence_offset;
+            if (x < mxf->partitions_count - 1) {
+                if (mxf->partitions[x+1].this_partition < p->essence_offset) {
+                    p->essence_length = -1;
+                } else
+                    p->essence_length = mxf->partitions[x+1].this_partition - p->essence_offset;
+            }
 
             if (p->essence_length < 0) {
                 /* next ThisPartition < essence_offset */
-- 
2.17.1