fix(video): validate PipeWire chunk ranges and accept NV12 - #2871
fix(video): validate PipeWire chunk ranges and accept NV12#2871kixelated wants to merge 8 commits into
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Two problems in the PipeWire screen capture path, both reachable today on the shared-memory path that every compositor currently uses. The chunk header was trusted as-is. `offset` is a ring position within the allocation rather than a guaranteed-in-range index, `size` is only what the producer wrote, and neither was checked against the rows `convert` goes on to sample. A short or mislabeled buffer produced a silent dropped frame at best. Wrap the offset, clamp the size to `maxsize`, and compute the byte span through the last sampled row up front, so a buffer that cannot hold a complete frame is rejected with a reason instead. The stride fallback also assumed 4 bytes per pixel, which is only true for the packed RGB layouts. That made NV12 unrepresentable, so the format offer never asked for it even though compositors commonly prefer it. Offer NV12 last (packed RGB stays preferred) and deinterleave it to I420, keying the chroma plane off the unclamped source height so an odd-height source does not read its last luma row as chroma. An empty chunk (`SPA_CHUNK_FLAG_EMPTY`) now skips alongside a corrupted one. It means "nothing new", so the existing pacing tick re-emits the last real frame rather than the capture forwarding a frame with no pixels. Verified on Linux with libpipewire 1.6.8: `cargo clippy -p moq-video --features pipewire --all-targets` clean, and the six new unit tests pass alongside the existing suite. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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WalkthroughPipeWire capture now advertises and processes NV12 frames. Frame processing normalizes chunk offsets and sizes, handles wrapped data, validates buffer coverage, and creates color-aware neutral frames for empty chunks. Conversion supports strided NV12 deinterleaving and packed RGB through Merge Risk: 🟠 High · up to Valid padded NV12 captures may still fail on the first frame and stop video capture, so the PR is not ready to merge until the required buffer span is corrected or the failure is safely contained. 🚥 Pre-merge checks | ✅ 5✅ Passed checks (5 passed)
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In `@rs/moq-video/src/capture/pipewire.rs`:
- Around line 579-600: Update nv12_to_i420 so the UV-plane slice and per-row
indexing consume only width bytes per row, matching frame_data_size’s
width-precise buffer contract and avoiding any requirement for trailing padding
after the final UV row. Add a regression test for nv12_to_i420 using exactly the
byte count returned by frame_data_size for a padded NV12 layout, ensuring
conversion succeeds without the final row’s padding.
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rs/moq-video/src/capture/pipewire.rsrs/moq-video/src/frame.rs
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| let uv_len = stride | ||
| .checked_mul(height / 2) | ||
| .ok_or_else(|| Error::Codec(anyhow::anyhow!("NV12 chroma size overflow")))?; | ||
| if stride < width || data.len() < y_len + uv_len { |
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When stride > width, the process callback passes exactly frame_data_size(...) bytes, which deliberately stops at the last visible chroma byte, but this check requires stride * (source_height + height / 2) bytes and therefore includes padding after the final chroma row. For the added 4x2 test layout with stride 6, production passes 16 bytes while this helper requires 18, so every padded-stride NV12 frame fails conversion and stops capture. Validate and slice each final row by its visible width, and add a regression test that exercises the production-sized slice. (Written by GPT-5.6 Sol)
AGENTS.md reference: AGENTS.md:L123-L123
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| if size == 0 || data.chunk().flags().contains(spa::buffer::ChunkFlags::CORRUPTED) { | ||
| // An empty chunk means "nothing new", so the pacing tick below | ||
| // keeps re-emitting the last real frame. | ||
| if size == 0 || data.chunk().flags().intersects(skip_flags()) { |
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When a compositor marks a video chunk SPA_CHUNK_FLAG_EMPTY, PipeWire defines that flag as neutral media such as a black frame, not as “nothing new.” Skipping it here leaves state.last unchanged, so after an EMPTY black frame the pacing timer can keep publishing the previous screen contents indefinitely. Synthesize the format's neutral frame, or convert any supplied pixels, rather than treating EMPTY like CORRUPTED. (Written by GPT-5.6 Sol)
AGENTS.md reference: AGENTS.md:L100-L100
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Co-Authored-By: OpenAI Codex <noreply@openai.com>
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| .checked_sub(1)?, | ||
| _ => height.checked_sub(1)?, | ||
| }; | ||
| last_row.checked_mul(stride)?.checked_add(row_size) |
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When a packed RGB frame has stride > width * 4, this calculation slices the input to (height - 1) * stride + width * 4, but I420::from_bgra and from_rgba pass that slice to the yuv converter, which validates a strided image against stride * height. The conversion therefore returns an error and the process callback stops capture for padded RGB buffers. The new NV12 regression test does not cover this separate packed-RGB path; retain the full final stride for these formats or repack the rows before conversion. (Written by GPT-5.6 Sol)
AGENTS.md reference: AGENTS.md:L123-L123
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| return; | ||
| }; | ||
| let Some(bytes) = bytes.get(offset..offset + size) else { | ||
| let Some(bytes) = bytes.get(offset..end) else { |
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When the normalized offset is nonzero and offset + required > maxsize, the PipeWire chunk's valid data wraps from the allocation tail to its head, but this contiguous get(offset..end) returns None and silently drops the frame even though required <= size. The helper-only offset test covers modulo normalization but not this production slice, so offsets such as 18 in a 16-byte allocation still fail whenever the frame crosses the boundary; assemble the tail and head before conversion or otherwise process both spans. (Written by GPT-5.6 Sol)
AGENTS.md reference: AGENTS.md:L123-L123
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| packed[packed_uv + row * width..packed_uv + (row + 1) * width] | ||
| .copy_from_slice(&uv[row * stride..row * stride + width]); | ||
| } | ||
| I420::from_nv12(&packed, width as u32, height as u32) |
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When PipeWire negotiates NV12 with an explicit full-range or non-size-default color matrix, this deinterleaves the samples through I420::from_nv12, which returns color: None, while the negotiated VideoInfoRaw color range and matrix are discarded. encode::Config::resolved_color then substitutes the size-based, always-limited Color::infer, so the encoded VUI disagrees with the captured samples and produces crushed full-range or incorrectly tinted output. Propagate the negotiated color into capture and encoder configuration, or normalize the samples into the inferred space, and cover the non-default range/matrix case with a regression test. (Written by GPT-5.6 Sol)
AGENTS.md reference: AGENTS.md:L123-L123
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| } | ||
| spa::sys::SPA_VIDEO_COLOR_MATRIX_BT709 => true, | ||
| spa::sys::SPA_VIDEO_COLOR_MATRIX_BT601 => false, | ||
| _ => return None, |
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When PipeWire declares NV12 with a valid SPA matrix such as BT.2020 or SMPTE 240M, this arm returns None. camera.color() then supplies None to the encoder config, whose resolved_color substitutes size-inferred BT.601/709 rather than leaving the VUI unspecified, so these samples remain mislabeled and display with incorrect colors. Fresh evidence in this revision is this fallback arm after the prior color fix; represent or normalize these matrices, or reject such a negotiation, and cover the case with a regression test. (Written by GPT-5.6 Sol)
AGENTS.md reference: AGENTS.md:L123-L123
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| encoder_config.bitrate = encode.bitrate; | ||
| encoder_config.codec = encode.codec; | ||
| encoder_config.kind = encode.kind.clone(); | ||
| encoder_config.color = camera.color(); |
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When PipeWire renegotiates the NV12 range or matrix without changing dimensions, param_changed retains the stream because it only restarts for geometry changes, while subsequent frames are tagged from the new state.format. This line configures the encoder only once from the initial pending frame, so its fixed VUI remains in the old color space and the encoder's mismatch path merely warns while continuing to publish incorrectly labeled video. Restart capture and encoding on any color-affecting format change, with a same-size renegotiation regression test. (Written by GPT-5.6 Sol)
AGENTS.md reference: AGENTS.md:L123-L123
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| if format.format() != VideoFormat::NV12 { | ||
| return Ok(None); | ||
| } | ||
| color_from_pipewire(format.color_range(), format.color_matrix(), Size::new(width, height)) |
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When NV12 supplies a supported BT.601/709 matrix and range but explicit color_primaries or transfer_function values incompatible with that Color, this call ignores those fields and accepts the format. The encoder expands Color into a fixed primaries/transfer/matrix VUI tuple, so the unchanged samples are mislabeled and can render with the wrong gamut or transfer curve. Validate the remaining VideoInfoRaw color fields, reject combinations Color cannot represent, and cover an explicit mismatch with a regression test. (Written by GPT-5.6 Sol)
AGENTS.md reference: AGENTS.md:L123-L123
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| tracing::warn!(width = size.width, height = size.height, "unusable capture size"); | ||
| return; | ||
| } | ||
| let color = match pipewire_color(state.format, width, height) { |
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When a same-size NV12 renegotiation omits optional color properties after the previous format supplied them, VideoInfoRaw::parse leaves those absent fields unchanged in this reused state.format. Consequently, this call observes the old range and matrix, format_requires_restart sees no change, and subsequent samples continue to be encoded under the stale color description. Parse each format into a fresh VideoInfoRaw before assigning it, and cover an explicit-to-omitted color renegotiation with a regression test. (Written by GPT-5.6 Sol)
AGENTS.md reference: AGENTS.md:L123-L123
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| if range == spa::sys::SPA_VIDEO_COLOR_RANGE_UNKNOWN && matrix == spa::sys::SPA_VIDEO_COLOR_MATRIX_UNKNOWN { | ||
| return Ok(None); |
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When an NV12 format leaves both range and matrix unknown but supplies explicit metadata such as BT.2020 primaries or a PQ transfer function, this early return bypasses validate_pipewire_description. The encoder then infers BT.601/709 and emits a VUI that contradicts the negotiated metadata. Fresh evidence in this revision is that the newly added validator is only called for Some(color); validate the explicit fields before this return and add a regression test for the unknown-range/matrix case. (Written by GPT-5.6 Sol)
AGENTS.md reference: AGENTS.md:L123-L123
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Summary
Split out of #2839, which bundled this with the Linux DMA-BUF work. These fixes stand alone, are reachable today on the shared-memory path every compositor currently uses, and are unit-testable without hardware.
offsetis a ring position within the allocation rather than a guaranteed-in-range index,sizeis only what the producer wrote, and neither was checked against the rowsconvertgoes on to sample. A short or mislabeled buffer produced a silently dropped frame at best. Now the offset normalizes, wrapped shared-memory chunks are reassembled, the size clamps tomaxsize, and each converter's required byte span is computed up front, so an incomplete frame is rejected with a reason.publish_captureconfigures the encoder. Unsupported or incompatible matrix, primaries, and transfer descriptions are rejected, and a same-size color renegotiation restarts capture so the encoder's fixed VUI cannot become stale. Each renegotiation is parsed into fresh state so omitted optional fields reset to unknown.SPA_CHUNK_FLAG_EMPTY) now emits neutral media. SPA defines the flag as media-specific neutral data, so capture publishes black I420 in the negotiated range instead of replaying old pixels.The DMA-BUF negotiation,
Surface::DmaBuf, and the Vulkan import stay on #2839.Public API changes
None.
I420::from_nv12anddeinterleave_uvarepub(crate); their#[cfg]widens from Windows-only to also cover Linux +pipewire.Test plan
nix develop --accept-flake-config --command cargo test -p moq-video --features pipewire --lib: 83 passed, 1 interactive portal test ignorednix develop --accept-flake-config --command cargo clippy -p moq-video --features pipewire --all-targets -- -D warningsnix develop --accept-flake-config --command cargo fmt -p moq-videogit diff --checkNo Cross-Package Sync row applies: this is internal to
moq-video's Linux capture backend, with no wire, FFI, or CLI surface.(Written by Claude Opus 5 and OpenAI Codex)