[jeffqjiangNew]

Motivation

A review pass over avc_parser.cpp turned up three out-of-bounds accesses in the slice
header's reference picture handling. All three share the same shape: the loop index is not
derived from a syntax element at all, it is bounded only by a terminator value appearing
in the bitstream. A stream that simply never emits the terminator runs the index without
limit.

The slice header is parsed into a stack local (AvcVideoParser::ParseNalUnit()), so an
unterminated list walks off the end of a stack object.

Two of the three arrays are also sized smaller than the specification allows, so the last
legal entry of a conforming stream already wrote one element past the end. That means a
bare capacity check would have rejected valid streams; the arrays are resized as well.

The third finding is a read-side overflow with a correctness bug attached, described below.

Technical Details

Ref pic list modification — ParseSliceHeader()

modification_l0 and modification_l1 were filled by do { ... } while (modification_of_pic_nums_idc != 3). The index had no bound other than that terminator,
against arrays of AVC_MAX_REF_PICTURE_NUM (32) entries.

7.4.3.1 bounds the list: the number of entries with modification_of_pic_nums_idc not equal
to 3 shall not exceed num_ref_idx_lX_active_minus1 + 1. Both loops are now capped at
num_ref_idx_lX_active_minus1 + 1, allowing for the terminating entry.
num_ref_idx_lX_active_minus1 is already range checked to 31 or less on every path that
reaches these loops — the PPS defaults at ParsePps() and the slice override at
ParseSliceHeader(), whose check is inside the same slice_type guard that gates the L0
loop, with the L1 loop reachable only for B slices — so the largest index is 32.

That is one past the end of a 32-entry array, and it is reachable from a conforming stream:
a field-coded slice may carry 32 active references and 32 modification entries, plus the
terminator. Both arrays are therefore sized with a new AVC_MAX_REF_LIST_MOD_NUM, 32
entries plus the terminator.

Decoded reference picture marking — ParseSliceHeader()

The MMCO loop has the same structure, terminating on
memory_management_control_operation == 0, writing into mmco[AVC_MAX_REF_PICTURE_NUM].

Unlike the modification lists, the specification places no single limit on the number of
MMCO operations in a slice, so the previous size of 32 was an assumption rather than a
bound. A limit is derived instead: each of the up to 32 reference fields can be marked
unused for reference by operation 1 or 2 and be assigned a long term frame index by
operation 3 or 6, plus one operation 4, one operation 5, and the terminating operation 0.
That becomes AVC_MAX_MMCO_NUM (67), the array is resized to it, and the loop is capped
by it.

Ref pic list modification process — ModifiyRefList()

ModifiyRefList() is called once per list, receiving modification_l0 or modification_l1
as a parameter, but the advance at the bottom of its while loop was hardcoded to
p_slice_header->ref_pic_list.modification_l0 regardless. Only the first entry came from
the array the caller passed.

This is an out-of-bounds read as well as a correctness bug. The loop's only exit condition
is finding modification_of_pic_nums_idc == 3 in the array it is walking. On the L1 call it
looked for that terminator in L0's array, and when ref_pic_list_modification_flag_l0 is 0
nothing was ever parsed into modification_l0 for this slice — the slice header is an
uninitialized stack local, copied wholesale into slice_info_list_, so the walk searched
indeterminate memory for a terminator that need not be there.

The fix saves the base pointer on entry and advances within the list the caller passed.
Indexing by ref_idx_lx is unchanged and remains correct: each iteration consumes exactly
one entry and increments ref_idx_lx exactly once, for modification_of_pic_nums_idc 0, 1
and 2 alike, so the entry index and ref_idx_lx stay in step.

This also corrects list 1 construction, which previously drew on list 0's operations
whenever an L1 modification carried more than one entry.

Debug dump — PrintSliceHeader()

The three dump loops iterated a hardcoded 32 entries, which after the resizes would print
neither the full modification lists nor a meaningful fraction of the MMCO array. They now
follow the new sizes and stop at the terminator, and at mmco_count for the MMCO dump. This
runs only at ROCDEC_LOG_LEVEL=4.

Issue Tracking

JIRA ID: ROCM-31875, AICV-310

Test Plan

Run /validate

Test Result

Full validation passed.

╔══════════════════════════════╗
║ rocDecode Validation Summary ║
╠══════════════════════════════╣
║ CTest (16 tests) ✓ PASSED ║
║ Conformance AVC ✓ PASSED ║
║ Conformance AV1 ✓ PASSED ║
║ Conformance HEVC ✓ PASSED ║
║ Conformance VP9 ✓ PASSED ║
╠══════════════════════════════╣
║ Overall ✓ PASSED ║
╚══════════════════════════════╝

Conformance breakdown

┌───────┬─────────┬────────┬────────┬────────────┐
│ Codec │ Streams │ Passed │ Failed │ Unfinished │
├───────┼─────────┼────────┼────────┼────────────┤
│ AVC │ 127 │ 127 │ 0 │ 0 │
├───────┼─────────┼────────┼────────┼────────────┤
│ AV1 │ 162 │ 162 │ 0 │ 0 │
├───────┼─────────┼────────┼────────┼────────────┤
│ HEVC │ 135 │ 135 │ 0 │ 0 │
├───────┼─────────┼────────┼────────┼────────────┤
│ VP9 │ 108 │ 108 │ 0 │ 0 │
├───────┼─────────┼────────┼────────┼────────────┤
│ Total │ 532 │ 532 │ 0 │ 0 │
└───────┴─────────┴────────┴────────┴────────────┘

Submission Checklist

• Look over the contributing guidelines at https://github.com/ROCm/rocm-systems/blob/develop/CONTRIBUTING.md.

[therock-pr-bot]

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[Copilot]

Copilot review overview

🟢 Approval recommended

The changes consistently prevent the identified overflows while preserving valid AVC limits and correcting L1 processing.

Review effort: Balanced
Findings: None

What changed in this PR

Bounds AVC reference-list and MMCO parsing to prevent out-of-bounds access while correcting list-1 modification handling.

Changes:

• Adds correctly sized limits for modification and MMCO arrays.
• Enforces parser bounds on bitstream-driven loops.
• Corrects list selection and debug output iteration.

File	Description
projects/​rocdecode/​src/​parser/​avc_parser.cpp	Adds bounds checks, fixes list traversal, and updates debug dumps.
projects/​rocdecode/​src/​parser/​avc_defines.h	Defines expanded capacities for modification and MMCO entries.

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[systems-assistant]

TheRock Submodule Bump Activity

Newest first

• 2026-10-05 — Included in TheRock via ROCm/TheRock#8732.