fix(release): stop re-scanning bytes VirusTotal has already scanned

.github/workflows/release.yml

@@ -316,10 +316,23 @@ jobs:
       # install.sh and install.ps1 are the highest-consequence non-executable
       # bytes we publish: users pipe them straight into a shell.
       #
-      # The selected executables are re-submitted too. That is deliberate and
-      # nearly free: VirusTotal is content-addressed, so identical bytes return
-      # the analysis it already holds instead of re-running 70+ engines — the
-      # same property that made the analysis-id equality check untenable.
+      # The selected executables are NOT re-submitted. They were scanned as
+      # candidates, and verify-release-selection.py has just proven every
+      # published container carries exactly those bytes — identity is settled by
+      # hash, so a second scan adds no assurance.
+      #
+      # It also is not free, contrary to what this comment used to claim.
+      # Measured on v0.10.5: all eight re-submissions produced a NEW analysis
+      # (same file-id, timestamp 47 minutes later), and Microsoft's ML engine
+      # answered differently for two of them within that hour — in opposite
+      # directions. The release notes then cited one scan while the links showed
+      # the other. See scripts/ci/exclude-rescanned-selected-objects.sh.
+      - name: Withhold already-scanned selected executables
+        run: |
+          bash scripts/ci/exclude-rescanned-selected-objects.sh \
+            binaries/objects "$RUNNER_TEMP/release-selection.tsv" \
+            binaries/virustotal-withheld.tsv
+
       - name: VirusTotal scan of every extracted release object
         uses: crazy-max/ghaction-virustotal@936d8c5c00afe97d3d9a1af26d017cfdf26800a2 # v5.0.0
         id: virustotal

scripts/ci/exclude-rescanned-selected-objects.sh

@@ -0,0 +1,101 @@
+#!/usr/bin/env bash
+# Withhold the selected executables from the full-surface VirusTotal pass.
+#
+# WHY (measured, not assumed). The verify pass used to submit every extracted
+# object, selected executables included, on the stated grounds that "VirusTotal
+# is content-addressed, so identical bytes return the analysis it already holds
+# instead of re-running 70+ engines". That is not what happens. On the v0.10.5
+# release all EIGHT re-submissions produced a NEW analysis: same VirusTotal
+# file-id, a timestamp 47 minutes later.
+#
+#   candidate: file-id=2c00f485...  ts=1786795957  (12:12:37Z)
+#   verify   : file-id=2c00f485...  ts=1786798758  (12:59:18Z)
+#
+# Re-analysing identical bytes re-rolls a probabilistic classifier, and it
+# answered differently in the same hour, in both directions:
+#
+#   82750cd1 (linux-amd64)   microsoft-ml -> clean
+#   6d3c5be6 (darwin-arm64)  clean        -> microsoft-ml
+#
+# The published release notes then cited the candidate verdict while the linked
+# page showed the verify verdict, so the table said "clean" for a binary
+# VirusTotal was flagging and vice versa. Nothing about the binaries differed:
+# same sha256 in both scans.
+#
+# The second scan also proved nothing the first did not. Identity is already
+# established by hash: verify-release-selection.py reconciles every published
+# container to the selected bytes before this step runs, and checksums.txt binds
+# the same digests publicly. A re-scan adds no assurance and one more roll.
+#
+# What still gets scanned is everything the candidate pass never saw: install.sh,
+# install.ps1, LICENSE, THIRD_PARTY_NOTICES.md, the MCPB manifest.json and the
+# unpacked UI assets. install.sh and install.ps1 are the highest-consequence
+# non-executable bytes we publish - users pipe them straight into a shell - and
+# that coverage is untouched.
+#
+# Fails closed: if nothing matches, the selection binding is broken; if nothing
+# is left, the surface scan would silently become a no-op.
+#
+# Usage: exclude-rescanned-selected-objects.sh <objects-dir> <release-selection.tsv> [manifest-out]
+set -euo pipefail
+
+OBJECTS_DIR="${1:?usage: exclude-rescanned-selected-objects.sh <objects-dir> <selection.tsv> [manifest-out]}"
+SELECTION="${2:?usage: exclude-rescanned-selected-objects.sh <objects-dir> <selection.tsv> [manifest-out]}"
+MANIFEST="${3:-}"
+
+test -d "$OBJECTS_DIR" || { echo "error: no objects directory: $OBJECTS_DIR" >&2; exit 1; }
+test -s "$SELECTION" || { echo "error: no selection evidence: $SELECTION" >&2; exit 1; }
+
+head -n 1 "$SELECTION" | grep -qx '# cbm-release-selection-v1' || {
+  echo "error: wrong evidence marker in $SELECTION" >&2; exit 1; }
+
+# selected_sha256 is the 4th column; skip the '#' metadata block and the header.
+selected="$(mktemp)"
+withheld="$(mktemp)"
+trap 'rm -f "$selected" "$withheld"' EXIT
+# `|| true` on the grep: with `set -o pipefail` a zero-match grep would abort the
+# script here, before the explicit check below could say why. A guard that exits
+# silently is not a guard.
+awk -F '\t' '/^#/ {next} $1=="target" {next} {print $4}' "$SELECTION" \
+  | { grep -E '^[0-9a-f]{64}$' || true; } | sort -u > "$selected"
+if [ ! -s "$selected" ]; then
+  echo "error: no selected sha256 values in $SELECTION — the selection" >&2
+  echo "       evidence names no shipped bytes, so nothing can be matched." >&2
+  exit 1
+fi
+
+kept=0
+for f in "$OBJECTS_DIR"/*; do
+  [ -f "$f" ] || continue
+  sha="$(sha256sum "$f" | awk '{print $1}')"
+  if grep -qx "$sha" "$selected"; then
+    printf '%s\t%s\n' "$sha" "$(basename "$f")" >> "$withheld"
+    rm -f -- "$f"
+  else
+    kept=$((kept + 1))
+  fi
+done
+
+count="$(wc -l < "$withheld" | tr -d ' ')"
+if [ "$count" -eq 0 ]; then
+  echo "error: no extracted object matched a selected sha256 — the release" >&2
+  echo "       containers do not carry the bytes the selection recorded." >&2
+  exit 1
+fi
+if [ "$kept" -eq 0 ]; then
+  echo "error: every extracted object was withheld; the full-surface scan" >&2
+  echo "       would cover nothing." >&2
+  exit 1
+fi
+
+if [ -n "$MANIFEST" ]; then
+  {
+    echo "# cbm-virustotal-withheld-v1"
+    echo "# reason=already-scanned-as-candidate"
+    echo "# evidence=virustotal-candidate-results.tsv"
+    printf 'sha256\tobject\n'
+    cat "$withheld"
+  } > "$MANIFEST"
+fi
+
+echo "withheld $count already-scanned selected executable(s); $kept object(s) remain for the surface scan"