[PATCH] libmakepkg/integrity: handle PGP signature files containing multiple signatures

[Jonas Witschel]

PGP signature files can contain multiple signatures from different keys. In
this case, verification is considered to be successful if *all* signatures are
valid, compare e.g. the behaviour of the gpgv verification tool.

parse_gpg_statusfile() is currently not equipped to handle the gpg output for
such signature files: it assumes that the file contains only one signature and
therefore overwrites the verification results of previous signatures,
effectively only considering the last signature in the file.

Therefore the logic needs to be refined so that $success and $trusted are only
true if all signatures are valid and trusted, respectively. We also need to
store the verification results per key (in order to present more specific error
messages) and all the validated fingerprints (in order to check whether they
are in validpgpkeys).

The signatures for the source tarballs of recent GnuPG releases, e.g. version
2.2.35, are examples of such signature files.

Signed-off-by: Jonas Witschel <diabonas at archlinux.org>
---
 .../integrity/verify_signature.sh.in          | 115 ++++++++++--------
 1 file changed, 65 insertions(+), 50 deletions(-)

diff --git a/scripts/libmakepkg/integrity/verify_signature.sh.in b/scripts/libmakepkg/integrity/verify_signature.sh.in
index ad5bb66d..4aa14d94 100644
--- a/scripts/libmakepkg/integrity/verify_signature.sh.in
+++ b/scripts/libmakepkg/integrity/verify_signature.sh.in
@@ -26,6 +26,18 @@ LIBRARY=${LIBRARY:-'@libmakepkgdir@'}
 source "$LIBRARY/util/message.sh"
 source "$LIBRARY/util/pkgbuild.sh"
 
+# Returns the elements of the first array that are not found in the second
+# array as the third array. All arrays are passed by name.
+set_difference() {
+	local -n first=$1
+	local -n second=$2
+	local -n result=$3
+	result=()
+	for element in "${first[@]}"; do
+		! in_array "$element" "${second[@]}" && result+=("$element")
+	done
+}
+
 check_pgpsigs() {
 	(( SKIPPGPCHECK )) && return 0
 	! source_has_signatures && return 0
@@ -56,48 +68,53 @@ check_pgpsigs() {
 		fi
 
 		# these variables are assigned values in parse_gpg_statusfile
-		success=0
-		status=
-		pubkey=
-		fingerprint=
+		success=
+		declare -A status
+		fingerprints=()
 		trusted=
 		parse_gpg_statusfile "$statusfile"
 		if (( ! $success )); then
 			printf '%s' "$(gettext "FAILED")" >&2
-			case "$status" in
-				"missingkey")
-					printf ' (%s)' "$(gettext "unknown public key") $pubkey" >&2
-					;;
-				"revokedkey")
-					printf " ($(gettext "public key %s has been revoked"))" "$pubkey" >&2
-					;;
-				"bad")
-					printf ' (%s)' "$(gettext "bad signature from public key") $pubkey" >&2
-					;;
-				"error")
-					printf ' (%s)' "$(gettext "error during signature verification")" >&2
-					;;
-			esac
+			for pubkey in "${!status[@]}"; do
+				case "${status["$pubkey"]}" in
+					"missingkey")
+						printf ' (%s)' "$(gettext "unknown public key") $pubkey" >&2
+						;;
+					"revokedkey")
+						printf " ($(gettext "public key %s has been revoked"))" "$pubkey" >&2
+						;;
+					"bad")
+						printf ' (%s)' "$(gettext "bad signature from public key") $pubkey" >&2
+						;;
+					"error")
+						printf ' (%s)' "$(gettext "error during signature verification")" >&2
+						;;
+				esac
+			done
 			errors=1
 		else
+			local invalid_keys
+			set_difference fingerprints validpgpkeys invalid_keys
 			if (( ${#validpgpkeys[@]} == 0 && !trusted )); then
-				printf "%s ($(gettext "the public key %s is not trusted"))" $(gettext "FAILED") "$fingerprint" >&2
+				printf "%s ($(gettext "the public key %s is not trusted"))" $(gettext "FAILED") "${fingerprints[*]}" >&2
 				errors=1
-			elif (( ${#validpgpkeys[@]} > 0 )) && ! in_array "$fingerprint" "${validpgpkeys[@]}"; then
-				printf "%s (%s %s)" "$(gettext "FAILED")" "$(gettext "invalid public key")" "$fingerprint" >&2
+			elif (( ${#validpgpkeys[@]} > 0 )) && (( ${#invalid_keys[@]} > 0 )); then
+				printf "%s (%s %s)" "$(gettext "FAILED")" "$(gettext "invalid public key")" "${invalid_keys[*]}" >&2
 				errors=1
 			else
 				printf '%s' "$(gettext "Passed")" >&2
-				case "$status" in
-					"expired")
-						printf ' (%s)' "$(gettext "WARNING:") $(gettext "the signature has expired.")" >&2
-						warnings=1
-						;;
-					"expiredkey")
-						printf ' (%s)' "$(gettext "WARNING:") $(gettext "the key has expired.")" >&2
-						warnings=1
-						;;
-				esac
+				for pubkey in "${!status[@]}"; do
+					case "${status["$pubkey"]}" in
+						"expired")
+							printf " (%s $(gettext "the signature by key %s has expired."))" "$(gettext "WARNING:")" "$pubkey" >&2
+							warnings=1
+							;;
+						"expiredkey")
+							printf " (%s $(gettext "the key %s has expired."))" "$(gettext "WARNING:")" "$pubkey" >&2
+							warnings=1
+							;;
+					esac
+				done
 			fi
 		fi
 		printf '\n' >&2
@@ -201,59 +218,57 @@ verify_git_signature() {
 parse_gpg_statusfile() {
 	local type arg1 arg6 arg10
 
+	success=-1
+	trusted=-1
 	while read -r _ type arg1 _ _ _ _ arg6 _ _ _ arg10 _; do
 		case "$type" in
 			GOODSIG)
-				pubkey=$arg1
-				success=1
-				status="good"
+				success=$((success!=0))
+				status["$arg1"]="good"
 				;;
 			EXPSIG)
-				pubkey=$arg1
-				success=1
-				status="expired"
+				success=$((success!=0))
+				status["$arg1"]="expired"
 				;;
 			EXPKEYSIG)
-				pubkey=$arg1
-				success=1
-				status="expiredkey"
+				success=$((success!=0))
+				status["$arg1"]="expiredkey"
 				;;
 			REVKEYSIG)
-				pubkey=$arg1
 				success=0
-				status="revokedkey"
+				status["$arg1"]="revokedkey"
 				;;
 			BADSIG)
-				pubkey=$arg1
 				success=0
-				status="bad"
+				status["$arg1"]="bad"
 				;;
 			ERRSIG)
-				pubkey=$arg1
 				success=0
 				if [[ $arg6 == 9 ]]; then
-					status="missingkey"
+					status["$arg1"]="missingkey"
 				else
-					status="error"
+					status["$arg1"]="error"
 				fi
 				;;
 			VALIDSIG)
 				if [[ $arg10 ]]; then
 					# If the file was signed with a subkey, arg10 contains
 					# the fingerprint of the primary key
-					fingerprint=$arg10
+					fingerprints+=("$arg10")
 				else
-					fingerprint=$arg1
+					fingerprints+=("$arg1")
 				fi
 				;;
 			TRUST_UNDEFINED|TRUST_NEVER)
 				trusted=0
 				;;
 			TRUST_MARGINAL|TRUST_FULLY|TRUST_ULTIMATE)
-				trusted=1
+				trusted=$((trusted!=0))
 				;;
 		esac
 	done < "$1"
+	success=$((success>0))
+	trusted=$((trusted>0))
 }
 
 source_has_signatures() {
-- 
2.36.1