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>
`banger kernel import <name> --from <dir>` copies a staged kernel
bundle into the local catalog. <dir> is the output of
`make void-kernel` or `make alpine-kernel` (build/manual/void-kernel/
or build/manual/alpine-kernel/).
kernelcat.DiscoverPaths locates artifacts under <dir>:
1. Prefers metadata.json (written by make-void-kernel.sh).
2. Falls back to globbing: boot/vmlinux-* or vmlinuz-* (Alpine
fallback), boot/initramfs-*, lib/modules/<latest>.
The daemon's KernelImport copies kernel + optional initrd via
system.CopyFilePreferClone and modules via system.CopyDirContents
(no-sudo mode — catalog lives under ~/.local/state), computes SHA256
over the kernel, and writes the manifest via kernelcat.WriteLocal.
While wiring this up, fixed a latent bug in system.CopyDirContents:
filepath.Join(sourceDir, ".") silently drops the trailing dot, so
`cp -a source source/contents target/` was copying the whole source
directory (including its basename) instead of just its contents.
Replaced the join with a manual "/." suffix. imagemgr.StageBootArtifacts
(the only existing caller) silently benefits.
scripts/register-void-image.sh and scripts/register-alpine-image.sh
are rewritten to use `banger kernel import … && banger image register
--kernel-ref …` instead of the find-and-pass-paths dance. Preserves
the same user-facing commands and env vars.
Tests cover: metadata.json preference, glob fallback, Alpine vmlinuz
fallback, kernel-missing error, round-trip copy into the catalog, and
the --from required flag.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Introduces a read/write kernel catalog on disk without any network
dependency, so later phases (image register --kernel-ref, import, pull)
can build on a working foundation.
Layout: adds KernelsDir to paths.Layout, ensured under
~/.local/state/banger/kernels/. Each cataloged kernel lives at
<KernelsDir>/<name>/ with a manifest.json alongside vmlinux and optional
initrd.img / modules/.
New internal/kernelcat package owns the disk format:
- Entry (Name, Distro, Arch, KernelVersion, SHA256, Source, ImportedAt)
- ValidateName (alphanumeric + dots/hyphens/underscores, no traversal)
- ReadLocal / ListLocal / WriteLocal / DeleteLocal
- SumFile helper
The daemon exposes three RPC methods dispatched in daemon.go:
kernel.list, kernel.show, kernel.delete. Implementations live in a new
internal/daemon/kernels.go and are thin wrappers over kernelcat using
d.layout.KernelsDir.
CLI: new top-level `banger kernel` with list / show / rm subcommands
mirroring the image-command pattern (ensureDaemon, RPC call, table or
JSON output). No sudo required — kernel ops are user-space only.
Users can now manually populate ~/.local/state/banger/kernels/<name>/
and see it via `banger kernel list`. Phase 2 wires --kernel-ref into
image register; Phase 3 adds `banger kernel import`; Phase 4 adds
remote pulls.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
