makepkg: Introduce validpgpkeys array

If validpgpkeys is set in the PKGBUILD, signature checking fails if
the fingerprint of the key used to create the signature is not listed
in the array.

The key's trust value is ignored.

Signed-off-by: Allan McRae <allan@archlinux.org>

doc/PKGBUILD.5.txt

@@ -128,6 +128,14 @@ Files in the source array with extensions `.sig`, `.sign` or, `.asc` are
 recognized by makepkg as PGP signatures and will be automatically used to verify
 the integrity of the corresponding source file.
 
+*validpgpkeys (array)*::
+	An array of PGP fingerprints. If this array is non-empty, makepkg will
+	only accept signatures from the keys listed here and will ignore the
+	trust values from the keyring. If the source file was signed with a
+	subkey, makepkg will still use the primary key for comparison.
++
+Fingerprints must be uppercase and must not contain whitespace characters.
+
 *noextract (array)*::
 	An array of file names corresponding to those from the source array. Files
 	listed here will not be extracted with the rest of the source files. This

scripts/makepkg.sh.in

@@ -1245,9 +1245,9 @@ check_checksums() {
 }
 
 parse_gpg_statusfile() {
-	local type arg1 arg6
+	local type arg1 arg6 arg10
 
-	while read -r _ type arg1 _ _ _ _ arg6 _; do
+	while read -r _ type arg1 _ _ _ _ arg6 _ _ _ arg10 _; do
 		case "$type" in
 			GOODSIG)
 				pubkey=$arg1
@@ -1283,6 +1283,15 @@ parse_gpg_statusfile() {
 					status="error"
 				fi
 				;;
+			VALIDSIG)
+				if [[ $arg10 ]]; then
+					# If the file was signed with a subkey, arg10 contains
+					# the fingerprint of the primary key
+					fingerprint=$arg10
+				else
+					fingerprint=$arg1
+				fi
+				;;
 			TRUST_UNDEFINED|TRUST_NEVER)
 				trusted=0
 				;;
@@ -1299,7 +1308,7 @@ check_pgpsigs() {
 
 	msg "$(gettext "Verifying source file signatures with %s...")" "gpg"
 
-	local file ext decompress found pubkey success status trusted
+	local file ext decompress found pubkey success status fingerprint trusted
 	local warning=0
 	local errors=0
 	local statusfile=$(mktemp)
@@ -1346,6 +1355,7 @@ check_pgpsigs() {
 		success=0
 		status=
 		pubkey=
+		fingerprint=
 		trusted=
 		parse_gpg_statusfile "$statusfile"
 		if (( ! $success )); then
@@ -1366,9 +1376,12 @@ check_pgpsigs() {
 			esac
 			errors=1
 		else
-			if (( ! $trusted )); then
+			if (( ${#validpgpkeys[@]} == 0 && ! $trusted )); then
 				printf "%s ($(gettext "the public key %s is not trusted"))" $(gettext "FAILED") "$pubkey" >&2
 				errors=1
+			elif (( ${#validpgpkeys[@]} > 0 )) && ! in_array "$fingerprint" "${validpgpkeys[@]}"; then
+				printf "%s (%s $pubkey)" "$(gettext "FAILED")" "$(gettext "invalid public key")"
+				errors=1
 			else
 				printf '%s' "$(gettext "Passed")" >&2
 				case "$status" in
@@ -2881,7 +2894,7 @@ fi
 
 unset pkgname pkgbase pkgver pkgrel epoch pkgdesc url license groups provides
 unset md5sums replaces depends conflicts backup source install changelog build
-unset makedepends optdepends options noextract
+unset makedepends optdepends options noextract validpgpkeys
 
 BUILDFILE=${BUILDFILE:-$BUILDSCRIPT}
 if [[ ! -f $BUILDFILE ]]; then