Container (and kernel) layers routinely ship symlinks with absolute
targets — /usr/bin/mawk, /lib/modules/<ver>/build, etc. Those are
interpreted relative to the rootfs at runtime (`/` inside the VM),
not against the host filesystem, so they are rooted inside dest by
construction and need no escape check at write time.
The previous logic resolved absolute Linknames literally (against
the host root), compared to the staging dir, and rejected everything
that didn't happen to live under it. That made `banger image pull
docker.io/library/debian:bookworm` fail on the very first symlink
("etc/alternatives/awk -> /usr/bin/mawk").
Relative targets still get the traversal check — a relative
Linkname with ../s can genuinely escape dest at write time even if
in-VM resolution would be safe — so the defense against malicious
relative chains is intact.
Tests:
- TestFlattenAcceptsAbsoluteSymlink replaces the old overly-strict
test, using the exact etc/alternatives/awk -> /usr/bin/mawk case
that broke debian:bookworm.
- TestFlattenRejectsRelativeSymlinkEscape confirms relative-with-
traversal is still rejected with the same "unsafe symlink"
error.
Same fix applied in internal/kernelcat/fetch.go for consistency;
future kernel bundles with absolute symlinks in the modules tree
would otherwise hit the same wall.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Introduces the headline feature of the kernel catalog: pulling a kernel
bundle over HTTP without any local build step.
Catalog format (internal/kernelcat/catalog.go):
- Catalog { Version, Entries } + CatEntry { Name, Distro, Arch,
KernelVersion, TarballURL, TarballSHA256, SizeBytes, Description }.
- catalog.json is embedded via go:embed and ships with each banger
binary. It starts empty (Phase 5's CI pipeline will populate it).
- Lookup(name) returns the matching entry or os.ErrNotExist.
Fetch (internal/kernelcat/fetch.go):
- HTTP GET with streaming SHA256 over the response body.
- zstd-decode (github.com/klauspost/compress/zstd) -> tar extract into
<kernelsDir>/<name>/.
- Hardens against path-traversal tarball entries (members whose
normalised path escapes the target dir, and unsafe symlink
targets) and sha256-mismatch downloads; any failure removes the
partially-populated target dir.
- Regular files, directories, and safe symlinks are supported; other
tar types (hardlinks, devices, fifos) are silently skipped.
- After extraction, recomputes sha256 over the on-disk vmlinux and
writes the manifest with Source="pull:<url>".
Daemon methods (internal/daemon/kernels.go):
- KernelPull(ctx, {Name, Force}) - lookup in embedded catalog, refuse
overwrite unless Force, delegate to kernelcat.Fetch.
- KernelCatalog(ctx) - return the embedded catalog annotated per-entry
with whether it has been pulled locally.
RPC: kernel.pull, kernel.catalog dispatch cases.
CLI:
- `banger kernel pull <name> [--force]`.
- `banger kernel list --available` prints the catalog with a
pulled/available STATE column and a human-readable size.
Tests: fetch round-trip (extract + manifest + sha256), sha256 mismatch
rejection with cleanup, missing-vmlinux rejection, path-traversal
rejection, HTTP error propagation, catalog parsing, lookup,
pulled-status reconciliation. All 20 packages green.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
