vp8l: reject images with dimensions exceeding 128 megapixels

[herdiyana256]

A crafted VP8L header with width=16384 and height=16384 (the
maximum values encodable in 14-bit fields) causes decodePix to
allocate 41638416384 = 1,073,741,824 bytes (~1 GB) per Decode
call. The allocation succeeds silently: Decode returns a nil
error, so callers cannot detect or limit the resource consumption.

Attack: a 28-byte file is sufficient to trigger the allocation.
No authentication or special knowledge is required. Five concurrent
requests produce ~5.37 GB of heap pressure, enough to OOM-kill a
typical containerized service.

Fix: add a pixel-count guard in decodeHeader, before any pixel
data is read, that returns an error when width*height exceeds
1<<27 (~128 megapixels; 512 MB at 4 bytes per pixel).

This is consistent with:

• The guard added to the tiff decoder for CVE-2026-33809
  (x/image/tiff: OOM from malicious IFD offset go#78267, fixed in v0.38.0)
• The existing VP8X canvas-size check in webp/decode.go

A regression test is included: TestDecodeOversizedDimensions
verifies that the crafted 28-byte input returns an error without
allocating the 1 GB buffer.

Updates golang/go#78267

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Patch Set 1:

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Message from herdiyanitdev:

Patch Set 1:

(1 comment)

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Patch Set 2:

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Patch Set 3: Code-Review+1

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