[FFmpeg-devel] [PATCH 2/2] avformat/matroskaenc: Fix and simplify check for invalid crop values

[Andreas Rheinhardt <andreas.rheinhardt@outlook.com>]

The check "left >= INT_MAX - right" is supposed to check for
whether left + right does not overflow/wraparound, but given that
left and top are uint32_t INT_MAX - right can already wraparound
for big values of right (and ordinary 32-bit ints):
If right == UINT32_MAX, INT_MAX - right is INT_MAX + 1;
for left in 0..par->width both checks will be passed.

Fix this and simplify the check by using 64-bit types,
where the addition is guaranteed not to overflow.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
---
 libavformat/matroskaenc.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/libavformat/matroskaenc.c b/libavformat/matroskaenc.c
index e1adc0eba6..4b91283119 100644
--- a/libavformat/matroskaenc.c
+++ b/libavformat/matroskaenc.c
@@ -1786,16 +1786,14 @@ static int mkv_write_track_video(AVFormatContext *s, MatroskaMuxContext *mkv,
                                  st->codecpar->nb_coded_side_data,
                                  AV_PKT_DATA_FRAME_CROPPING);
     if (sd && sd->size == sizeof(uint32_t) * 4) {
-        uint32_t top, bottom, left, right;
+        uint64_t top, bottom, left, right;
 
         top    = AV_RL32(sd->data +  0);
         bottom = AV_RL32(sd->data +  4);
         left   = AV_RL32(sd->data +  8);
         right  = AV_RL32(sd->data + 12);
 
-        if (left >= INT_MAX - right ||
-            top >= INT_MAX - bottom ||
-            (left + right) >= par->width ||
+        if ((left + right) >= par->width ||
             (top + bottom) >= par->height) {
             av_log(s, AV_LOG_ERROR, "Invalid cropping dimensions in stream side data\n");
             return AVERROR(EINVAL);
-- 
2.40.1

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