initrd/gpg: fix passphrase fd leaks and review issues

Replace --passphrase-file with --passphrase-fd 3 3< <(...)
to avoid leaking the PIN value through /proc/<pid>/cmdline
of the child echo/printf process in factory reset, card
identity, and key import commands.

Also fix 6 instances of $? clobbered by intervening
TRACE_FUNC/DEBUG calls.  Fix algo_code extraction to
use head -1 against multi-key outputs.  Fix STATUS_OK
on public partition mount (only on success).  Return
actual hotp_verification error code.

Signed-off-by: Thierry Laurion <insurgo@riseup.net>

Author: tlaurion

initrd/etc/gpg_functions.sh

@@ -192,7 +192,7 @@ gpg_card_factory_reset() {
 		echo y             # confirm
 		echo yes           # confirm
 	} | DO_WITH_DEBUG gpg --command-fd=0 --status-fd=1 --pinentry-mode=loopback \
-		--passphrase-file <(echo -n "$card_admin_pin") --card-edit \
+		--passphrase-fd 3 3< <(echo -n "$card_admin_pin") --card-edit \
 		>/tmp/gpg_card_edit_output 2>&1
 	rc=$?
 	TRACE_FUNC
@@ -339,7 +339,7 @@ gpg_set_card_identity() {
 		fi
 		echo "quit"
 	} | DO_WITH_DEBUG gpg --command-fd=0 --status-fd=2 --pinentry-mode=loopback \
-		--passphrase-file <(printf '%s' "$card_admin_pin") --card-edit \
+		--passphrase-fd 3 3< <(echo -n "$card_admin_pin") --card-edit \
 		>/tmp/gpg_card_edit_output 2>&1 ||
 		DIE "Failed to set identity fields on OpenPGP smartcard"
 
@@ -511,7 +511,7 @@ reprovision_smartcard_from_backup() {
 	# Phase 3: import the private key (master + subkeys) into ~/.gnupg.
 	# --import-options restore brings in the full key material.
 	STATUS "Importing GPG keys from backup"
-	if ! gpg --pinentry-mode=loopback --passphrase-file <(printf '%s' "$admin_pin") \
+	if ! gpg --pinentry-mode=loopback --passphrase-fd 3 3< <(echo -n "$admin_pin") \
 		--import-options restore --import /media/privkey.sec >/dev/null 2>/tmp/gpg_import_err; then
 		umount /media 2>/dev/null || true
 		ERROR="$(cat /tmp/gpg_import_err)"