Fixes: out of array access
Fixes: 
62603/clusterfuzz-testcase-minimized-ffmpeg_DEMUXER_fuzzer-5837632490569728

Found-by: continuous fuzzing process 
https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
---
 libavcodec/cbs_h266_syntax_template.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/libavcodec/cbs_h266_syntax_template.c 
b/libavcodec/cbs_h266_syntax_template.c
index 5654f22878..5a34200a18 100644
--- a/libavcodec/cbs_h266_syntax_template.c
+++ b/libavcodec/cbs_h266_syntax_template.c
@@ -2043,9 +2043,12 @@ static int FUNC(pps) (CodedBitstreamContext *ctx, 
RWContext *rw,
                 }
                 if (i < current->pps_num_slices_in_pic_minus1) {
                     if (current->pps_tile_idx_delta_present_flag) {
+                        // Two conditions must be met:
+                        // 1. −NumTilesInPic + 1 <= pps_tile_idx_delta_val[i] 
<= NumTilesInPic − 1
+                        // 2. 0 <= tile_idx + pps_tile_idx_delta_val[i] <= 
NumTilesInPic − 1
+                        // Combining these conditions yields: -tile_idx <= 
pps_tile_idx_delta_val[i] <= NumTilesInPic - 1 - tile_idx
                         ses(pps_tile_idx_delta_val[i],
-                            -current->num_tiles_in_pic + 1,
-                            current->num_tiles_in_pic - 1, 1, i);
+                            -tile_idx, current->num_tiles_in_pic - 1 - 
tile_idx, 1, i);
                         if (current->pps_tile_idx_delta_val[i] == 0) {
                             av_log(ctx->log_ctx, AV_LOG_ERROR,
                                    "pps_tile_idx_delta_val[i] shall not be 
equal to 0.\n");
-- 
2.25.1

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