From d4e452b67b6cf78aff45415f80da3b12aa5ad5f5 Mon Sep 17 00:00:00 2001
From: Ben <ben@nousresearch.com>
Date: Sat, 23 May 2026 14:59:42 +1000
Subject: [PATCH] fix(docker): SHA256-verify s6-overlay tarballs
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PR #30136 review flagged the s6-overlay install as a supply-chain
regression vs the gosu source it replaced — `tianon/gosu` was
digest-pinned via `FROM ...@sha256:...`, but the three new
ADD/curl downloads had no integrity check at all.

Pin all three tarballs (noarch, symlinks-noarch, per-arch) to
upstream-published SHA256s via ARGs. Verification happens via
`sha256sum -c` against a single checksum file (avoids a piped-shell
hadolint DL4006 warning under dash). To bump S6_OVERLAY_VERSION,
fetch the four `.sha256` files from the new release and update
the ARGs — documented inline.

If upstream artifacts are tampered with mid-build, the build now
fails loudly at the verification step instead of silently
producing a tainted image.
---
 Dockerfile | 22 +++++++++++++++++++---
 1 file changed, 19 insertions(+), 3 deletions(-)

diff --git a/Dockerfile b/Dockerfile
index d350dbeefba..eb5d9fb7e15 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -34,22 +34,38 @@ RUN apt-get update && \
 # — splitting one URL per arch into two ADDs would download both on every
 # build and leave dead bytes in the cache. A single curl + arch-keyed URL
 # is simpler and cache-friendlier.
+#
+# Supply-chain integrity: every tarball is checksum-verified against the
+# upstream-published SHA256. To bump S6_OVERLAY_VERSION, fetch the four
+# `.sha256` files from the corresponding release and update the ARGs. The
+# checksum lookup happens during build, so a compromised release artifact
+# fails the build loudly instead of silently producing a tampered image.
 ARG TARGETARCH
 ARG S6_OVERLAY_VERSION=3.2.3.0
+ARG S6_OVERLAY_NOARCH_SHA256=b720f9d9340efc8bb07528b9743813c836e4b02f8693d90241f047998b4c53cf
+ARG S6_OVERLAY_X86_64_SHA256=a93f02882c6ed46b21e7adb5c0add86154f01236c93cd82c7d682722e8840563
+ARG S6_OVERLAY_AARCH64_SHA256=0952056ff913482163cc30e35b2e944b507ba1025d78f5becbb89367bf344581
+ARG S6_OVERLAY_SYMLINKS_SHA256=a60dc5235de3ecbcf874b9c1f18d73263ab99b289b9329aa950e8729c4789f0e
 ADD https://github.com/just-containers/s6-overlay/releases/download/v${S6_OVERLAY_VERSION}/s6-overlay-noarch.tar.xz /tmp/
 ADD https://github.com/just-containers/s6-overlay/releases/download/v${S6_OVERLAY_VERSION}/s6-overlay-symlinks-noarch.tar.xz /tmp/
 RUN set -eu; \
     case "${TARGETARCH:-amd64}" in \
-        amd64) s6_arch="x86_64" ;; \
-        arm64) s6_arch="aarch64" ;; \
+        amd64) s6_arch="x86_64"; s6_arch_sha="${S6_OVERLAY_X86_64_SHA256}" ;; \
+        arm64) s6_arch="aarch64"; s6_arch_sha="${S6_OVERLAY_AARCH64_SHA256}" ;; \
         *) echo "Unsupported TARGETARCH=${TARGETARCH} for s6-overlay" >&2; exit 1 ;; \
     esac; \
     curl -fsSL --retry 3 -o /tmp/s6-overlay-arch.tar.xz \
         "https://github.com/just-containers/s6-overlay/releases/download/v${S6_OVERLAY_VERSION}/s6-overlay-${s6_arch}.tar.xz"; \
+    { \
+        printf '%s  %s\n' "${S6_OVERLAY_NOARCH_SHA256}" /tmp/s6-overlay-noarch.tar.xz; \
+        printf '%s  %s\n' "${s6_arch_sha}" /tmp/s6-overlay-arch.tar.xz; \
+        printf '%s  %s\n' "${S6_OVERLAY_SYMLINKS_SHA256}" /tmp/s6-overlay-symlinks-noarch.tar.xz; \
+    } > /tmp/s6-overlay.sha256; \
+    sha256sum -c /tmp/s6-overlay.sha256; \
     tar -C / -Jxpf /tmp/s6-overlay-noarch.tar.xz; \
     tar -C / -Jxpf /tmp/s6-overlay-arch.tar.xz; \
     tar -C / -Jxpf /tmp/s6-overlay-symlinks-noarch.tar.xz; \
-    rm /tmp/s6-overlay-*.tar.xz
+    rm /tmp/s6-overlay-*.tar.xz /tmp/s6-overlay.sha256
 
 # Non-root user for runtime; UID can be overridden via HERMES_UID at runtime
 RUN useradd -u 10000 -m -d /opt/data hermes