build: Sign RPM packages (#8046)

.github/scripts/strategy-matrix/linux.json

@@ -92,7 +92,7 @@
         "build_type": ["Release"],
         "arch": ["amd64"],
         "minimal": false,
-        "image": "ghcr.io/xrplf/xrpld/packaging-debian:sha-028ccea"
+        "image": "ghcr.io/xrplf/xrpld/packaging-debian:sha-a6983f8"
       }
     ],
 
@@ -102,7 +102,7 @@
         "build_type": ["Release"],
         "arch": ["amd64"],
         "minimal": false,
-        "image": "ghcr.io/xrplf/xrpld/packaging-rhel:sha-028ccea"
+        "image": "ghcr.io/xrplf/xrpld/packaging-rhel:sha-a6983f8"
       }
     ]
   }

.github/workflows/on-tag.yml

@@ -49,3 +49,4 @@ jobs:
     secrets:
       remote_username: ${{ secrets.NEXUS_REMOTE_USERNAME }}
       remote_password: ${{ secrets.NEXUS_REMOTE_PASSWORD }}
+      signing_key: ${{ secrets.NEXUS_PACKAGES_PRIVATE_KEY }}

.github/workflows/on-trigger.yml

@@ -120,3 +120,4 @@ jobs:
     secrets:
       remote_username: ${{ secrets.NEXUS_REMOTE_USERNAME }}
       remote_password: ${{ secrets.NEXUS_REMOTE_PASSWORD }}
+      signing_key: ${{ secrets.NEXUS_PACKAGES_PRIVATE_KEY }}

.github/workflows/reusable-package.yml

@@ -29,6 +29,9 @@ on:
       remote_password:
         description: "The password or token for that Nexus account."
         required: false
+      signing_key:
+        description: "Armoured PGP private key used to sign the RPMs. Required when publishing."
+        required: false
 
 defaults:
   run:
@@ -98,6 +101,14 @@ jobs:
           PKG_CHANNEL: ${{ steps.release_info.outputs.channel }}
         run: ./package/build_pkg.sh
 
+      # Before the upload, so the artifact and the published package are the
+      # same bytes. DEBs are not signed, so the key is never set on that job.
+      - name: Sign RPM
+        if: ${{ inputs.publish && matrix.distro == 'rhel' }}
+        env:
+          PKG_SIGNING_KEY: ${{ secrets.signing_key }}
+        run: ./package/sign_rpm.sh "${BUILD_DIR}"
+
       - name: Upload package artifact
         uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a # v7.0.1
         with:

package/README.md

@@ -9,6 +9,7 @@ a build configured with `-Dvalidator_keys=ON`.
 ```
 package/
   build_pkg.sh        Staging and build script (called by the CMake `package` target and CI)
+  sign_rpm.sh         Signs the built RPMs (called by CI when publishing)
   publish_pkg.sh      Uploads built packages to the XRPLF Nexus repositories (called by CI)
   rpm/
     xrpld.spec      RPM spec
@@ -32,7 +33,7 @@ package manager (`apt-get` -> deb, `dnf`/`yum` -> rpm).
 
 | Package type | Image (`package_configs.<distro>[].image` in `linux.json`) | Tools required                                      |
 | ------------ | ---------------------------------------------------------- | --------------------------------------------------- |
-| RPM          | `ghcr.io/xrplf/xrpld/packaging-rhel:sha-<sha>`             | `rpmbuild`                                          |
+| RPM          | `ghcr.io/xrplf/xrpld/packaging-rhel:sha-<sha>`             | `rpmbuild`, `rpmsign`                               |
 | DEB          | `ghcr.io/xrplf/xrpld/packaging-debian:sha-<sha>`           | `dpkg-buildpackage`, debhelper with compat level 13 |
 
 To print the full packaging matrix (artifact names and images) for the current
@@ -152,11 +153,14 @@ any `XRPLF` repository, `on-pr.yml` never. Both authenticate with the
 `NEXUS_REMOTE_USERNAME` / `NEXUS_REMOTE_PASSWORD` secrets already used for the
 Conan remote.
 
-Nexus owns the repository metadata; nothing here signs or indexes anything. Worth
-knowing:
+Nexus owns the repository metadata; nothing here indexes anything. Worth knowing:
 
 - Each apt-hosted repository needs a distribution and a PGP signing keypair
-  configured in Nexus, which rejects one created without a keypair.
+  configured in Nexus, which rejects one created without a keypair. Nexus signs
+  the apt metadata with it, never the packages.
+- Hosted yum repositories cannot be signed by Nexus at all, so `sign_rpm.sh`
+  signs the RPMs before they are uploaded, and rpm clients verify with
+  `gpgcheck=1` rather than `repo_gpgcheck=1`.
 - yum metadata is rebuilt asynchronously, so a successful publish is not
   immediately installable.
 - Each job uploads only what it built, and uploads are not transactional, so a
@@ -212,8 +216,12 @@ fail early.
 Flags are for explicit invocation; environment variables are intended for
 CMake/CI integration. The CI workflow and the CMake `package` target both invoke
 `build_pkg.sh` with no flags; CMake supplies `SRC_DIR`, `BUILD_DIR`, and
-`PKG_RELEASE` via env, while CI supplies `BUILD_DIR` and `PKG_RELEASE` via env
-and lets the script use defaults for the rest.
+`PKG_RELEASE` via env, while CI supplies `BUILD_DIR`, `PKG_RELEASE` and
+`PKG_CHANNEL` via env and lets the script use defaults for the rest.
+
+Signing is not part of this script. `sign_rpm.sh` does it in a separate CI step
+that only runs when publishing, so a published RPM is always signed and a local
+build never needs a key.
 
 It resolves `SRC_DIR` and `BUILD_DIR` to absolute paths, then calls
 `stage_common()` to copy the `xrpld` and `validator-keys` binaries, config files,

package/sign_rpm.sh

@@ -0,0 +1,65 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+# Sign the RPMs built by build_pkg.sh. Nexus cannot sign hosted yum metadata, so
+# the packages carry the signature themselves and rpm clients verify them with
+# gpgcheck=1.
+#
+# Usage: sign_rpm.sh [package-dir]
+#
+#   package-dir  searched recursively for *.rpm ('build' by default)
+#
+# PKG_SIGNING_KEY must hold an armoured PGP private key. It has no flag, to keep
+# the key out of the process list.
+#
+# There is no DEB equivalent: apt trusts the repository metadata, which Nexus
+# signs, rather than the packages themselves.
+
+pkg_dir="${1:-build}"
+
+mapfile -d '' rpms < <(find "${pkg_dir}" -type f -name '*.rpm' -print0)
+
+# Signing nothing would otherwise look like a successful signing.
+if [[ ${#rpms[@]} -eq 0 ]]; then
+    echo "sign_rpm.sh: no RPMs found in ${pkg_dir}." >&2
+    exit 1
+fi
+
+: "${PKG_SIGNING_KEY:?is required}"
+
+# Global, and expanded by the trap when it fires: the keyring holds an
+# unencrypted private key, so it must go even if signing fails.
+signing_home="$(mktemp -d)"
+trap 'rm -rf "${signing_home}"' EXIT
+export GNUPGHOME="${signing_home}"
+
+printf '%s' "${PKG_SIGNING_KEY}" | gpg --batch --quiet --import
+
+# Exactly one secret key, so that picking the first below is not a guess between
+# several.
+secrets="$(gpg --list-secret-keys --with-colons | grep -c '^sec:' || true)"
+if [[ "${secrets}" -ne 1 ]]; then
+    echo "sign_rpm.sh: PKG_SIGNING_KEY must hold exactly one secret key, found ${secrets}." >&2
+    exit 1
+fi
+
+key="$(gpg --list-secret-keys --with-colons | awk -F: '/^fpr:/ { print $10; exit }')"
+echo "Signing ${#rpms[@]} RPM(s) with ${key}."
+
+# Loopback pinentry: the key is unattended, so there is no tty to prompt on.
+rpmsign \
+    --define "_gpg_name ${key}" \
+    --define "_gpg_sign_cmd_extra_args --pinentry-mode loopback --batch --yes" \
+    --addsign "${rpms[@]}"
+
+# rpmsign can exit 0 having attached nothing, and an unsigned package is only
+# rejected later, on the installing machine. Both header tags are checked
+# because an RSA signature lands in RSAHEADER and a DSA or EdDSA one in
+# DSAHEADER.
+for pkg in "${rpms[@]}"; do
+    signature="$(rpm --query --queryformat '%{RSAHEADER:pgpsig}%{DSAHEADER:pgpsig}' --package "${pkg}")"
+    if [[ "${signature}" == "(none)(none)" ]]; then
+        echo "sign_rpm.sh: ${pkg} is unsigned after rpmsign." >&2
+        exit 1
+    fi
+done