ffmpeg | branch: master | Andreas Rheinhardt <andreas.rheinha...@outlook.com> | 
Mon Feb 26 22:37:04 2024 +0100| [1bb7d5ca9fc6dc1b961014255ada03dee40bac31] | 
committer: Andreas Rheinhardt

avformat/mov: Don't use entry[-1] in pointer arithmetic

It is undefined behaviour.
Fixes many failed tests with UBSan and GCC 13 like
"src/libavformat/mov.c:4229:44: runtime error: store to address
0x5572abe20f80 with insufficient space for an object of type 'struct
MOVIndexRange'"
(The line number does not refer to the line where &entry[-1]
is assigned.)

Reviewed-by: James Almer <jamr...@gmail.com>
Signed-off-by: Andreas Rheinhardt <andreas.rheinha...@outlook.com>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=1bb7d5ca9fc6dc1b961014255ada03dee40bac31
---

 libavformat/mov.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/libavformat/mov.c b/libavformat/mov.c
index 71e8f7ae8f..97caaa7723 100644
--- a/libavformat/mov.c
+++ b/libavformat/mov.c
@@ -4022,7 +4022,7 @@ static void mov_fix_index(MOVContext *mov, AVStream *st)
     int num_discarded_begin = 0;
     int first_non_zero_audio_edit = -1;
     int packet_skip_samples = 0;
-    MOVIndexRange *current_index_range;
+    MOVIndexRange *current_index_range = NULL;
     int found_keyframe_after_edit = 0;
     int found_non_empty_edit = 0;
 
@@ -4038,7 +4038,6 @@ static void mov_fix_index(MOVContext *mov, AVStream *st)
         return;
     }
     msc->current_index_range = msc->index_ranges;
-    current_index_range = msc->index_ranges - 1;
 
     // Clean AVStream from traces of old index
     sti->index_entries = NULL;
@@ -4225,8 +4224,9 @@ static void mov_fix_index(MOVContext *mov, AVStream *st)
             }
 
             // Update the index ranges array
-            if (current_index_range < msc->index_ranges || index != 
current_index_range->end) {
-                current_index_range++;
+            if (!current_index_range || index != current_index_range->end) {
+                current_index_range = current_index_range ? 
current_index_range + 1
+                                                          : msc->index_ranges;
                 current_index_range->start = index;
             }
             current_index_range->end = index + 1;
@@ -4289,7 +4289,8 @@ static void mov_fix_index(MOVContext *mov, AVStream *st)
     av_freep(&frame_duration_buffer);
 
     // Null terminate the index ranges array
-    current_index_range++;
+    current_index_range = current_index_range ? current_index_range + 1
+                                              : msc->index_ranges;
     current_index_range->start = 0;
     current_index_range->end = 0;
     msc->current_index = msc->index_ranges[0].start;

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