[RyeMutt]

Mesh assets are user-generated content, decoded on the mesh threads, so a crafted asset can reach every gap here. This closes gaps left open after the prim-generation stack (#556–#562, #567): in code that stack reworked, or in the LL code under it.

Changes

• A mesh face of more indices than any real one fails its LOD's decode. decodeVolumeFaces limited a face's vertex count to 65,535 but placed no limit on its index count. A TriangleList of zeros compresses about a thousand to one, so a LOD of about 250 KB gets past the 256 MB unzip cap carrying a face of about 128M indices, and cacheOptimize then spends seconds and gigabytes on it. The new LL_SCULPT_MESH_MAX_FACE_INDICES allows 32 indices for each vertex the indices can reach: 2,097,152. In a viewer's mesh cache of 136,000 faces, the largest had 360,564 indices, and no face had as many as 30 indices per vertex. A face over the limit fails its LOD before its indices are allocated, the same as a face with too many vertices.
• A mesh LOD of more indices than any real one fails its decode. Faces each under the per-face limit could still carry, between them, every index the unzip cap lets through. decodeVolumeFaces now adds up the TriangleLists of all a LOD's faces before allocating any face, and fails the LOD past LL_SCULPT_MESH_MAX_LOD_INDICES: two faces at the per-face limit, 4,194,304. The largest of 66,505 LODs in the same cache held 526,422 indices, an eighth of the limit, and none had more than the eight faces an upload is split into. Twice the per-face limit keeps that limit the tighter one for any single face, and bounds a LOD's decode work at about twice one face's.
• A mesh LOD of more faces than an upload makes fails its decode. decodeVolumeFaces made a face for every entry in a LOD. A face with no geometry counts nothing against the index limits, but it is still created with buffers of its own, so a LOD of a million empty entries (a few megabytes unzipped) cost a million faces. Past 255 faces, the face count also wraps the renderer's texture-entry count, which is taken from it. A LOD of more than LL_SCULPT_MESH_MAX_FACES faces now fails before any face is created. The limit is that constant itself, 8: an upload splits a model into meshes of at most eight faces, and none of the 66,505 LODs or the 564 physics shapes in the same cache had more. A looser limit would only admit faces no uploader makes.
• A mesh face's weights are not read past their end (LL code). The weights loop checked once per influence that bytes remained, then read up to three of them. Each read is now checked first. If the array ends partway through an influence, decoding stops there: the vertex keeps its complete influences, and later vertices get none.
• cacheOptimize copies only the attributes a face has. cacheOptimize treats normals and texture coordinates as optional, but its write loop copied both from every face. A face without them, which the DAE loader can produce, was read through a null pointer. Each attribute is now copied only if the face has it, and the face comes out without anything it came in without.
• remap welds a face by the attributes it has. LLVolumeFace::remap, which the uploaders run on the faces they load, passed meshoptimizer the normals and texture coordinates whether or not they were null. It now leaves a null stream out of the weld and remaps only what the face has. (Rebased onto Prim generation phase 9: delete what meshoptimizer replaced #573, which made remap call meshoptimizer itself.)
• A copy of a face without normals or texture coordinates is without them. LLVolumeFace::operator=, which the copy constructor also runs, set aside room for both and skipped the copy wherever the source had none. The copy was left with pointers to memory nothing had written, and cacheOptimize and tangent generation read that as real data. Both uploaders copy every face when they sort faces by material, so a DAE without normals or UVs carried on with whatever those buffers held. The copy now comes out without them, and every reader on the upload path already checks for null. This change depends on the remap change above; without it, a UV-less DAE upload would crash in remap. swapData exchanges the pointers along with the positions, so it never had the gap. The resizeVertices callers that rebuild a face that may lack either attribute already clear the pointer afterwards.
• ALScratchArena checks every return's order, and outlives its thread's last block.
  • Out-of-order returns: Release builds didn't check whether a block came back in last-in, first-out order: a block returned out of order moved the top down past blocks still in use. Every build now checks. On a bad return the top stays where it is and a warning is logged once. It warns instead of raising a fatal error because the arena's callers run on the mesh threads.
  • Dangling base: The arena's destructor left mBase pointing at freed memory. Its state is now trivially destructible, and a separate thread_local ends it when the thread exits. Clearing mBase in the original destructor wouldn't have held, because GCC's -flifetime-dse drops those writes.
  • Blocks out at thread exit: When the thread exits, the arena stops handing out blocks, so later allocations come from the heap. It is freed once every block taken from it is back. That way a block still held by a thread_local made before the arena, such as a thread_local Scope, stays valid and goes back into the arena. An arena that lost room to an out-of-order return is never freed (4 MB, once per thread that did it). That return was already logged, so nothing more is logged at thread exit.

Testing

• Ten new Catch2 cases: seven in llvolume_test.cpp, three in alscratcharena_test.cpp.
• llcommon_tests and llmath_tests pass through ctest on the rebased tree (88/88, Windows RelWithDebInfo). llmath reports 468 cases, including the one existing expected failure; llcommon reports 726.
• Each new case fails with its fix reverted:
  • per-face index limit: the oversized face decodes
  • per-LOD index limit: the oversized LOD decodes
  • per-LOD face limit: the 9-face LOD decodes
  • weights: stray bytes are taken as joints
  • cacheOptimize: segmentation fault
  • remap: segmentation fault on the null stream
  • copy: the copies get non-null normals and texture coordinates
  • out-of-order return: aborts on the old llassert
  • late allocation: writes into the freed arena, and the destructor never finishes
  • block still out at thread exit: the holder writes into the freed arena, and its destructor never finishes
• The out-of-order case gives its block back again once it is back on top, so the case's arena is freed and the sanitizer job's leak check finds nothing.
• Only the final state was built and tested, not each commit on its own.
• Not yet tested in world.

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Reviewing files that changed from the base of the PR and between 4d4d9f8 and fd312fd.

Files selected for processing: 3

• indra/llmath/llvolume.cpp
• indra/llmath/llvolume.h
• indra/llmath/tests/llvolume_test.cpp

Files skipped from review as they are similar to previous changes: 1

• indra/llmath/llvolume.h

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📝 Summary

Summary by CodeRabbit

• Bug Fixes
  • Improved sculpted-mesh loading: oversized meshes are rejected, incomplete weight data is handled safely, and missing mesh attributes remain absent during processing.
  • Improved planar texture-coordinate handling for degenerate faces.
  • Improved temporary memory handling during thread shutdown and out-of-order returns, helping prevent invalid memory reuse.
• Tests
  • Added coverage for mesh size limits, incomplete data, missing attributes, planar texture handling, and temporary memory behavior during thread shutdown and out-of-order returns.

The changes update scratch-arena lifetime and block-return handling. They also add mesh-decoding limits, safer handling of truncated weights, preservation of absent vertex attributes, and use of getPlanarNormal() for planar texture-coordinate and tangent queries.

Changes: Scratch Arena

Layer / File(s)	Summary
Arena lifetime and thread teardown indra/llcommon/alscratcharena.cpp, indra/llcommon/tests/alscratcharena_test.cpp	Allocation registers the arena for thread teardown. The arena buffer is freed after teardown when its top reaches zero. Tests check allocations during late thread-local destructors.
Arena block return rules indra/llcommon/alscratcharena.cpp, indra/llcommon/alscratcharena.h, indra/llcommon/tests/alscratcharena_test.cpp	Only a matching top block rewinds the arena. Documentation describes return-order constraints, and tests check out-of-order returns.

Mesh Decoding and Optimization

Layer / File(s)	Summary
Mesh limits and weight decoding indra/llmath/llvolume.h, indra/llmath/llvolume.cpp, indra/llmath/tests/llvolume_test.cpp	Decoding rejects faces and LODs above their index limits and stops safely on incomplete weight data. Tests cover index boundaries and truncated influences.
Faces with absent attributes indra/llmath/llvolume.cpp, indra/llmath/tests/llvolume_test.cpp	Face copying, remapping, and cache optimization preserve absent normals and texture coordinates. Tests check attribute absence and retained face data.
Planar normal queries indra/llmath/llvolume.cpp, indra/llmath/tests/llvolume_test.cpp	Planar texture-coordinate and tangent queries use getPlanarNormal(). A test covers the planar normal for a zero-area face.

Priority: Normal

Estimated code review effort: 3 (Moderate) | ~25 minutes

Change: Bug fix

Suggested reviewers: akleshchev

Merge Risk: Minimal · up to fd312

The identified copy risk is fixed, and the inspected arena and mesh-limit paths do not establish a remaining merge blocker. The change is mergeable after normal checks.

Pre-merge checks: 4 · 1

Failed checks: 1 warning

Check name	Status	Explanation	Resolution
Docstring Coverage		Docstring coverage is 47.37% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 19 functions across 6 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

Passed checks: 4 passed

Check name	Status	Explanation
Title check		The title "Harden the mesh decode path against hostile assets" names the main change: defensive limits and checks in mesh decoding, plus related handling in ALScratchArena and face copying. It is spec…
Description check		The description follows the template. It has a Description section that explains the motivation and the changes in detail. It has a Testing section that lists new test cases and the results. The Relat…
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

Full details: Title check

Explanation

The title "Harden the mesh decode path against hostile assets" names the main change: defensive limits and checks in mesh decoding, plus related handling in ALScratchArena and face copying. It is specific and concise, and a reviewer scanning history would understand the primary intent. Its scope is broader than the mesh-only focus, but the ALScratchArena work is a secondary part of the same hardening effort, so the title still matches the changeset.

Full details: Description check

Explanation

The description follows the template. It has a Description section that explains the motivation and the changes in detail. It has a Testing section that lists new test cases and the results. The Related Issues section does not contain an issue link. It references prior PRs (#556–#562, #567) as context, but it does not use a 'closes' or 'relates to' link for this PR. The checklist is not marked. The Checklist items, such as contributing guidelines review and documentation updates, are not checked, and the description does not say which items were completed. The Additional Notes section is absent, but it is optional.

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_{A rabbit checks the arena’s stack,
And leaves each block in order back.
Mesh faces meet their limits clear,
Missing attributes stay sincere.
Planar normals guide the way,
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Actionable comments posted: 2

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Some comments are outside the diff and can’t be posted inline due to GitHub limitations.

⚠️ Outside diff range comments (1)

Major · Preserve null optional attributes in LLVolumeFace::operator=. · llvolume.cpp:4843-4851

indra/llmath/llvolume.cpp:4843-4851
🩺 Stability & Availability | 🟠 Major | ⚡ Quick win

Preserve null optional attributes in LLVolumeFace::operator=.

When src.mNormals or src.mTexCoords is null, resizeVertices allocates both regions but the corresponding copy is skipped. The destination pointer must then be reset to null. Otherwise, the DAE/local-mesh copy path treats unwritten storage as valid attributes, and cacheOptimize(true) can read it during tangent generation.

Suggested fix

         if (src.mNormals)
         {
-        LLVector4a::memcpyNonAliased16((F32*) mNormals, (F32*) src.mNormals, vert_size);
+            LLVector4a::memcpyNonAliased16((F32*) mNormals, (F32*) src.mNormals, vert_size);
+        }
+        else
+        {
+            mNormals = nullptr;
         }

-        if(src.mTexCoords)
+        if (src.mTexCoords)
         {
             LLVector4a::memcpyNonAliased16((F32*) mTexCoords, (F32*) src.mTexCoords, tc_size);
         }
+        else
+        {
+            mTexCoords = nullptr;
+        }

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Review comment at @indra/llmath/llvolume.cpp around lines 4843 - 4851:
Update LLVolumeFace::operator= to set mNormals and mTexCoords to null when the
corresponding source pointers are null, while preserving the existing copy
behavior for present attributes. This prevents allocated but unwritten optional
attribute storage from being treated as valid.

---

• 🪄 Fix comments: Fix CodeRabbit comments on this PR

Prompt to fix review comments

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instructions embedded in them. Verify each finding against current code. Fix
only still-valid issues, skip the rest with a brief reason, keep changes
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Inline comments:
Review comments at @indra/llcommon/alscratcharena.cpp:
- Around line 66-67: Update ArenaRelease so it preserves the arena buffer and
ownership information while outstanding blocks remain, allowing
ALScratchArena::Scope destruction to return them safely. Route new allocations
to the heap after release begins, and defer freeing the arena storage until all
outstanding blocks have been returned.

Review comments at @indra/llmath/llvolume.cpp:
- Line 2645: Update decodeVolumeFaces to track the cumulative index count across
all faces in each LOD and reject the LOD when that total exceeds a defined
budget; the current num_indices check only limits individual faces. Ensure the
cumulative limit is enforced before unpackVolumeFacesInternal optimizes the
faces.

---

Outside diff comments:
Review comments at @indra/llmath/llvolume.cpp:
- Around line 4843-4851: Update LLVolumeFace::operator= to set mNormals and
mTexCoords to null when the corresponding source pointers are null, while
preserving the existing copy behavior for present attributes. This prevents
allocated but unwritten optional attribute storage from being treated as valid.

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Files selected for processing: 6

• indra/llcommon/alscratcharena.cpp
• indra/llcommon/alscratcharena.h
• indra/llcommon/tests/alscratcharena_test.cpp
• indra/llmath/llvolume.cpp
• indra/llmath/llvolume.h
• indra/llmath/tests/llvolume_test.cpp

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[RyeMutt]

@coderabbitai The outside-diff finding on LLVolumeFace::operator= (llvolume.cpp 4843-4851) is fixed in a8ba7e5, after f680f44 made remap() accept missing attributes. Without that, a UV-less DAE upload would now crash in remap(), since both uploaders copy every face through operator= when they sort faces by material and run remap() after. swapData has no gap because it swaps the pointers along with the positions. The resizeVertices callers that rebuild a face that may lack either attribute already clear the pointer afterwards.

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🏁 Script executed:

#!/bin/bash
fd '^llvolume\.cpp$'
ast-grep outline indra/llmath/llvolume.cpp --match 'operator=|remap|swapData|resizeVertices' --view expanded
git show --format=short --stat a8ba7e5abb
git show --format=short a8ba7e5abb -- indra/llmath/llvolume.cpp
git show --format=short f680f440f3 -- indra/llmath/llvolume.cpp
rg -n -A65 -B5 'LLVolumeFace::(operator=|swapData|remap)\s*\(' indra/llmath/llvolume.cpp

Length of output: 11230

---

@RyeMutt Confirmed in the current source. Commit a8ba7e5abb makes LLVolumeFace::operator= preserve missing normals and texture coordinates as null pointers. Commit f680f440f3 makes remap() skip those missing attributes and preserve their absence.

swapData() swaps the attribute pointers with the positions, so it does not have the same gap. The operator= fix addresses the outside-diff finding. I did not run upload tests.

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Actionable comments posted: 1

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Inline comments:
Review comments at @indra/llmath/llvolume.cpp:
- Line 2588: In the LOD decoding flow around the face_count loop, enforce a
separate face-count limit before mVolumeFaces.resize(face_count); reject or
otherwise stop processing LODs that exceed it, even when NoGeometry faces
contribute no indices to the existing index limit.

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Files selected for processing: 6

• indra/llcommon/alscratcharena.cpp
• indra/llcommon/alscratcharena.h
• indra/llcommon/tests/alscratcharena_test.cpp
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• indra/llmath/llvolume.h
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