Feat/bounded tar extraction - #5
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Add a Feature Briefing section requiring a plain-English what/why/how summary to the user before starting any roadmap feature. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Unbounded io.Copy let a malicious layer fill the disk (tar bomb), and symlink/hardlink targets were never checked against the extraction root. Add an Extractor with per-entry and cumulative size caps via LimitReader, reject absolute paths and ".." components, and validate symlink/hardlink targets stay in-tree (treating absolute targets literally so they cannot re-root through filepath.Join). Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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Why:
The extractor unpacked container image layers with an unbounded io.Copy, so a malicious or corrupted image could carry a tar bomb that inflates to fill the disk. Symlink and hardlink entries were also never validated against the extraction root, leaving a path-traversal hole. For a tool whose whole job is scanning untrusted images, both are unacceptable.
What changed:
Introduced an Extractor with configurable per-entry (FileSizeCap, default 512 MiB) and cumulative (TotalSizeCap, default 2 GiB) size caps, enforced via io.LimitReader.
Reject absolute paths and .. components before touching the filesystem.
Validate symlink/hardlink targets stay in-tree, treating absolute targets literally so they can't re-root through filepath.Join.
ExtractImage delegates to New().Untar(...) — no change to existing callers.
Added table-driven tests covering safe/rejected entries, size caps, and a multi-hop chained-symlink escape.
Verified: go test -race ./..., golangci-lint run, and govulncheck ./... all clean. No new dependencies.