[FFmpeg-devel] [PATCH] lavc/vvc: Validate temporal MVP references

[Frank Plowman <post@frankplowman.com>]

Per VVCv3 p. 157, the collocated reference picture used in temporal
motion vector prediction must have RprConstraintsActiveFlag equal to
zero and the same CTU size as the current picture.  Add these checks,
fixing crashes decoding some fuzzed bitstreams.

Additionally, only set up the collocated reference picture if it is
actually going to be used (i.e. if ph_temporal_mvp_enabled_flag is 1),
else legal RPR bitstreams will fail the new checks.

Co-authored-by: Nuo Mi <nuomi2021@gmail.com>
Signed-off-by: Frank Plowman <post@frankplowman.com>
---
 libavcodec/vvc/refs.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/libavcodec/vvc/refs.c b/libavcodec/vvc/refs.c
index fb42963034..8b7ba639a3 100644
--- a/libavcodec/vvc/refs.c
+++ b/libavcodec/vvc/refs.c
@@ -506,9 +506,14 @@ int ff_vvc_slice_rpl(VVCContext *s, VVCFrameContext *fc, SliceContext *sc)
                 return ret;
             }
         }
-        if ((!rsh->sh_collocated_from_l0_flag) == lx &&
-            rsh->sh_collocated_ref_idx < rpl->nb_refs)
-            fc->ref->collocated_ref = rpl->refs[rsh->sh_collocated_ref_idx].ref;
+        if (ph->r->ph_temporal_mvp_enabled_flag &&
+            (!rsh->sh_collocated_from_l0_flag) == lx &&
+            rsh->sh_collocated_ref_idx < rpl->nb_refs) {
+            const VVCRefPic *refp = rpl->refs + rsh->sh_collocated_ref_idx;
+            if (refp->is_scaled || refp->ref->sps->ctb_log2_size_y != sps->ctb_log2_size_y)
+                return AVERROR_INVALIDDATA;
+            fc->ref->collocated_ref = refp->ref;
+        }
     }
     return 0;
 }
-- 
2.44.0

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