[gentoo-dev] [PATCH 1/5] verify-sig.eclass: New eclass to verify OpenPGP sigs

[Michał Górny]

verify-sig eclass provides a streamlined approach to verifying upstream
signatures on distfiles.  Its primary purpose is to permit developers
to easily verify signatures while bumping packages.  The eclass removes
the risk of developer forgetting to perform the verification,
or performing it incorrectly, e.g. due to additional keys in the local
keyring.  It also permits users to verify the developer's work.
---
 eclass/verify-sig.eclass | 177 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 177 insertions(+)
 create mode 100644 eclass/verify-sig.eclass

diff --git a/eclass/verify-sig.eclass b/eclass/verify-sig.eclass
new file mode 100644
index 000000000000..8bf48446f427
--- /dev/null
+++ b/eclass/verify-sig.eclass
@@ -0,0 +1,177 @@
+# Copyright 2020 Gentoo Authors
+# Distributed under the terms of the GNU General Public License v2
+
+# @ECLASS: verify-sig.eclass
+# @MAINTAINER:
+# Michał Górny <mgorny@g.o>
+# @SUPPORTED_EAPIS: 7
+# @AUTHOR:
+# Michał Górny <mgorny@g.o>
+# @BLURB: Eclass to verify upstream signatures on distfiles
+# @DESCRIPTION:
+# verify-sig eclass provides a streamlined approach to verifying
+# upstream signatures on distfiles.  Its primary purpose is to permit
+# developers to easily verify signatures while bumping packages.
+# The eclass removes the risk of developer forgetting to perform
+# the verification, or performing it incorrectly, e.g. due to additional
+# keys in the local keyring.  It also permits users to verify
+# the developer's work.
+#
+# To use the eclass, start by packaging the upstream's key
+# as app-crypt/openpgp-keys-*.  Then inherit the eclass, add detached
+# signatures to SRC_URI and set VERIFY_SIG_OPENPGP_KEY_PATH.  The eclass
+# provides verify-sig USE flag to toggle the verification.
+#
+# Example use:
+# @CODE
+# inherit verify-sig
+#
+# SRC_URI="https://example.org/${P}.tar.gz
+#   verify-sig? ( https://example.org/${P}.tar.gz.sig )"
+# BDEPEND="
+#   verify-sig? ( app-crypt/openpgp-keys-example )"
+#
+# VERIFY_SIG_OPENPGP_KEY_PATH=/usr/share/openpgp-keys/example.asc
+# @CODE
+
+case "${EAPI:-0}" in
+	0|1|2|3|4|5|6)
+		die "Unsupported EAPI=${EAPI} (obsolete) for ${ECLASS}"
+		;;
+	7)
+		;;
+	*)
+		die "Unsupported EAPI=${EAPI} (unknown) for ${ECLASS}"
+		;;
+esac
+
+EXPORT_FUNCTIONS src_unpack
+
+if [[ ! ${_VERIFY_SIG_ECLASS} ]]; then
+
+IUSE="+verify-sig"
+
+BDEPEND="
+	verify-sig? (
+		app-crypt/gnupg
+		>=app-portage/gemato-16
+	)"
+
+# @ECLASS-VARIABLE: VERIFY_SIG_OPENPGP_KEY_PATH
+# @DEFAULT_UNSET
+# @DESCRIPTION:
+# Path to key bundle used to perform the verification.  This is required
+# when using default src_unpack.  Alternatively, the key path can be
+# passed directly to the verification functions.
+
+# @ECLASS-VARIABLE: VERIFY_SIG_OPENPGP_KEYSERVER
+# @DEFAULT_UNSET
+# @DESCRIPTION:
+# Keyserver used to refresh keys.  If not specified, the keyserver
+# preference from the key will be respected.  If no preference
+# is specified by the key, the GnuPG default will be used.
+
+# @ECLASS-VARIABLE: VERIFY_SIG_OPENPGP_KEY_REFRESH
+# @USER_VARIABLE
+# @DESCRIPTION:
+# Attempt to refresh keys via WKD/keyserver.  Set it to "yes"
+# in make.conf to enable.  Note that this requires working Internet
+# connection.
+: ${VERIFY_SIG_OPENPGP_KEY_REFRESH:=no}
+
+# @FUNCTION: verify-sig_verify_detached
+# @USAGE: <file> <sig-file> [<key-file>]
+# @DESCRIPTION:
+# Read the detached signature from <sig-file> and verify <file> against
+# it.  <key-file> can either be passed directly, or it defaults
+# to VERIFY_SIG_OPENPGP_KEY_PATH.  The function dies if verification
+# fails.
+verify-sig_verify_detached() {
+	local file=${1}
+	local sig=${2}
+	local key=${3:-${VERIFY_SIG_OPENPGP_KEY_PATH}}
+
+	[[ -n ${key} ]] ||
+		die "${FUNCNAME}: no key passed and VERIFY_SIG_OPENPGP_KEY_PATH unset"
+
+	local extra_args=()
+	[[ ${VERIFY_SIG_OPENPGP_KEY_REFRESH} == yes ]] || extra_args+=( -R )
+	[[ -n ${VERIFY_SIG_OPENPGP_KEYSERVER+1} ]] && extra_args+=(
+		--keyserver "${VERIFY_SIG_OPENPGP_KEYSERVER}"
+	)
+
+	einfo "Verifying ${file##*/} ..."
+	gemato gpg-wrap -K "${key}" "${extra_args[@]}" -- \
+		gpg --verify "${sig}" "${file}" ||
+		die "PGP signature verification failed"
+}
+
+# @FUNCTION: verify-sig_src_unpack
+# @DESCRIPTION:
+# Default src_unpack override that verifies signatures for all
+# distfiles if 'verify-sig' flag is enabled.  The function dies if any
+# of the signatures fails to verify or if any distfiles are not signed.
+# Please write src_unpack() yourself if you need to perform partial
+# verification.
+verify-sig_src_unpack() {
+	if use verify-sig; then
+		local f suffix found
+		local distfiles=() signatures=() nosigfound=() straysigs=()
+
+		# find all distfiles and signatures, and combine them
+		for f in ${A}; do
+			found=
+			for suffix in .sig; do
+				if [[ ${f} == *${suffix} ]]; then
+					signatures+=( "${f}" )
+					found=sig
+					break
+				else
+					if has "${f}${suffix}" ${A}; then
+						distfiles+=( "${f}" )
+						found=dist+sig
+						break
+					fi
+				fi
+			done
+			if [[ ! ${found} ]]; then
+				nosigfound+=( "${f}" )
+			fi
+		done
+
+		# check if all distfiles are signed
+		if [[ ${#nosigfound[@]} -gt 0 ]]; then
+			eerror "The following distfiles lack detached signatures:"
+			for f in "${nosigfound[@]}"; do
+				eerror "  ${f}"
+			done
+			die "Unsigned distfiles found"
+		fi
+
+		# check if there are no stray signatures
+		for f in "${signatures[@]}"; do
+			if ! has "${f%.*}" "${distfiles[@]}"; then
+				straysigs+=( "${f}" )
+			fi
+		done
+		if [[ ${#straysigs[@]} -gt 0 ]]; then
+			eerror "The following signatures do not match any distfiles:"
+			for f in "${straysigs[@]}"; do
+				eerror "  ${f}"
+			done
+			die "Unused signatures found"
+		fi
+
+		# now perform the verification
+		for f in "${signatures[@]}"; do
+			verify-sig_verify_detached \
+				"${DISTDIR}/${f%.*}" "${DISTDIR}/${f}"
+		done
+	fi
+
+	# finally, unpack the distfiles
+	default_src_unpack
+}
+
+_VERIFY_SIG_ECLASS=1
+fi
-- 
2.28.0