[FFmpeg-devel] [PATCH] cbs_h265: Ensure that a predicted RPS doesn't contain too many pictures

[Mark Thompson]

If the RPS we are predicting from has maximum size then at least one of
the pictures in it must be discarded before adding the current one.

Also revert 588114cea4ee434c9c61353ed91ffc817d2965f5, which added
now-redundant checks for the special case of a too-large RPS with all
pictures being in the same direction from the current one.
---
It would be helpful to test this on the fuzzing samples from 20446/clusterfuzz-testcase-minimized-ffmpeg_BSF_HEVC_METADATA_fuzzer-5707770718584832 which prompted the original incomplete fix.  Is there somewhere I can find them?

 libavcodec/cbs_h265_syntax_template.c | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/libavcodec/cbs_h265_syntax_template.c b/libavcodec/cbs_h265_syntax_template.c
index 5f5531944c..85ff5e5dc5 100644
--- a/libavcodec/cbs_h265_syntax_template.c
+++ b/libavcodec/cbs_h265_syntax_template.c
@@ -522,7 +522,7 @@ static int FUNC(st_ref_pic_set)(CodedBitstreamContext *ctx, RWContext *rw,
         infer(inter_ref_pic_set_prediction_flag, 0);
 
     if (current->inter_ref_pic_set_prediction_flag) {
-        unsigned int ref_rps_idx, num_delta_pocs;
+        unsigned int ref_rps_idx, num_delta_pocs, num_ref_pics;
         const H265RawSTRefPicSet *ref;
         int delta_rps, d_poc;
         int ref_delta_poc_s0[HEVC_MAX_REFS], ref_delta_poc_s1[HEVC_MAX_REFS];
@@ -538,18 +538,28 @@ static int FUNC(st_ref_pic_set)(CodedBitstreamContext *ctx, RWContext *rw,
         ref_rps_idx = st_rps_idx - (current->delta_idx_minus1 + 1);
         ref = &sps->st_ref_pic_set[ref_rps_idx];
         num_delta_pocs = ref->num_negative_pics + ref->num_positive_pics;
+        av_assert0(num_delta_pocs < HEVC_MAX_DPB_SIZE);
 
         flag(delta_rps_sign);
         ue(abs_delta_rps_minus1, 0, INT16_MAX);
         delta_rps = (1 - 2 * current->delta_rps_sign) *
             (current->abs_delta_rps_minus1 + 1);
 
+        num_ref_pics = 0;
         for (j = 0; j <= num_delta_pocs; j++) {
             flags(used_by_curr_pic_flag[j], 1, j);
             if (!current->used_by_curr_pic_flag[j])
                 flags(use_delta_flag[j], 1, j);
             else
                 infer(use_delta_flag[j], 1);
+            if (current->use_delta_flag[i])
+                ++num_ref_pics;
+        }
+        if (num_ref_pics >= HEVC_MAX_DPB_SIZE) {
+            av_log(ctx->log_ctx, AV_LOG_ERROR, "Invalid stream: "
+                   "short-term ref pic set %d "
+                   "contains too many pictures.\n", st_rps_idx);
+            return AVERROR_INVALIDDATA;
         }
 
         // Since the stored form of an RPS here is actually the delta-step
@@ -601,8 +611,6 @@ static int FUNC(st_ref_pic_set)(CodedBitstreamContext *ctx, RWContext *rw,
             }
         }
 
-        if (i > 15)
-            return AVERROR_INVALIDDATA;
         infer(num_negative_pics, i);
         for (i = 0; i < current->num_negative_pics; i++) {
             infer(delta_poc_s0_minus1[i],
@@ -632,8 +640,6 @@ static int FUNC(st_ref_pic_set)(CodedBitstreamContext *ctx, RWContext *rw,
             }
         }
 
-        if (i + current->num_negative_pics > 15)
-            return AVERROR_INVALIDDATA;
         infer(num_positive_pics, i);
         for (i = 0; i < current->num_positive_pics; i++) {
             infer(delta_poc_s1_minus1[i],
-- 
2.26.2