[Buildroot] [PATCH v3 7/8] package/petitboot: enable user separation

[Reza Arbab <arbab@linux.ibm.com>]

Run the petitboot UI as an unprivileged user. This requires using the
agetty package instead of the busybox getty utility, running the initial
pb-console helper at user login rather than directly.

If sudo is installed, with a sudoers policy allowing petituser to
perform sudo with no password (or a blank password), the "drop to shell"
feature of petitboot will automatically become a root shell.

Signed-off-by: Reza Arbab <arbab@linux.ibm.com>
---
 package/petitboot/Config.in      |  1 +
 package/petitboot/S15pb-discover |  4 +++-
 package/petitboot/pb-console     |  6 ++++--
 package/petitboot/petitboot.mk   | 12 ++++++++++++
 package/petitboot/shell_config   | 24 ++++++++++++++++++++++++
 package/petitboot/shell_profile  |  2 ++
 6 files changed, 46 insertions(+), 3 deletions(-)
 create mode 100644 package/petitboot/shell_config
 create mode 100644 package/petitboot/shell_profile

diff --git a/package/petitboot/Config.in b/package/petitboot/Config.in
index 5f1d91e77ecb..0f965e71e628 100644
--- a/package/petitboot/Config.in
+++ b/package/petitboot/Config.in
@@ -16,6 +16,7 @@ config BR2_PACKAGE_PETITBOOT
 	select BR2_PACKAGE_KEXEC_LITE if ( BR2_powerpc || BR2_powerpc64 || BR2_powerpc64le )
 	select BR2_PACKAGE_NVME if ( BR2_powerpc || BR2_powerpc64 || BR2_powerpc64le )
 	select BR2_PACKAGE_POWERPC_UTILS if ( BR2_powerpc || BR2_powerpc64 || BR2_powerpc64le )
+	select BR2_PACKAGE_UTIL_LINUX_AGETTY
 	help
 	  Petitboot is a small kexec-based bootloader
 
diff --git a/package/petitboot/S15pb-discover b/package/petitboot/S15pb-discover
index 71ab62d99859..a37e33521f1a 100644
--- a/package/petitboot/S15pb-discover
+++ b/package/petitboot/S15pb-discover
@@ -12,7 +12,9 @@ fi
 
 start() {
 	printf 'Starting %s: ' "$DAEMON"
-	mkdir -p /var/log/petitboot
+	# shellcheck disable=SC2174 # only apply -m to deepest dir
+	mkdir -p -m 0775 /var/log/petitboot
+	chown root:petitgroup /var/log/petitboot
 
 	# shellcheck disable=SC2086 # we need the word splitting
 	start-stop-daemon -S -q -b -m -p "$PIDFILE" -x "/usr/sbin/$DAEMON" \
diff --git a/package/petitboot/pb-console b/package/petitboot/pb-console
index 407ff3b30232..eea40163d02f 100644
--- a/package/petitboot/pb-console
+++ b/package/petitboot/pb-console
@@ -3,14 +3,16 @@
 DAEMON="pb-console"
 
 PB_CONSOLE_PORT=${2:-"console"}
-PB_CONSOLE_ARGS="--getty --detach -- -n -i 0 $PB_CONSOLE_PORT linux"
+PB_CONSOLE_ARGS="--getty=/sbin/agetty --detach -- -a petituser -n -i $PB_CONSOLE_PORT linux"
 
 # shellcheck source=/dev/null
 [ -r "/etc/default/petitboot" ] && . "/etc/default/petitboot"
 
 start() {
 	printf 'Starting %s on %s: ' "$DAEMON" "$PB_CONSOLE_PORT"
-	mkdir -p /var/log/petitboot
+	# shellcheck disable=SC2174 # only apply -m to deepest dir
+	mkdir -p -m 0775 /var/log/petitboot
+	chown root:petitgroup /var/log/petitboot
 
 	# shellcheck disable=SC2086 # we need the word splitting
 	start-stop-daemon -S -q -x "/usr/libexec/petitboot/$DAEMON" \
diff --git a/package/petitboot/petitboot.mk b/package/petitboot/petitboot.mk
index ff87f3498734..5b517eb3b1a6 100644
--- a/package/petitboot/petitboot.mk
+++ b/package/petitboot/petitboot.mk
@@ -71,6 +71,10 @@ define PETITBOOT_POST_INSTALL
 		$(TARGET_DIR)/usr/sbin/kexec-restart
 	$(INSTALL) -D -m 0755 $(PETITBOOT_PKGDIR)/pb-console \
 		$(TARGET_DIR)/etc/init.d/pb-console
+	$(INSTALL) -D -m 0755 $(PETITBOOT_PKGDIR)/shell_config \
+		$(TARGET_DIR)/home/petituser/.shrc
+	$(INSTALL) -D -m 0755 $(PETITBOOT_PKGDIR)/shell_profile \
+		$(TARGET_DIR)/home/petituser/.profile
 
 	mkdir -p $(TARGET_DIR)/etc/udev/rules.d
 	(for port in $(PETITBOOT_GETTY_PORT); do \
@@ -84,4 +88,12 @@ endef
 
 PETITBOOT_POST_INSTALL_TARGET_HOOKS += PETITBOOT_POST_INSTALL
 
+define PETITBOOT_USERS
+	petituser -1 petitgroup -1 * /home/petituser /bin/sh - petitboot user
+endef
+
+define PETITBOOT_PERMISSIONS
+	/var/petitboot d 775 root petitgroup - - - - -
+endef
+
 $(eval $(autotools-package))
diff --git a/package/petitboot/shell_config b/package/petitboot/shell_config
new file mode 100644
index 000000000000..b10b95baae6c
--- /dev/null
+++ b/package/petitboot/shell_config
@@ -0,0 +1,24 @@
+#!/bin/sh
+
+try_sudo() {
+	[ -x "$(command -v sudo)" ] || return
+	sudo -K
+	echo | sudo -S /bin/true >/dev/null 2>&1 || return
+
+	echo "No password required, running as root."
+	sudo -i
+	sudo -K
+	exit
+}
+
+reset
+
+echo "Exiting petitboot. Type 'exit' to return."
+echo "You may run 'pb-sos' to gather diagnostic data."
+
+if [ "$(id -u)" != "0" ]; then
+	try_sudo
+	export PS1='$ '
+else
+	export PS1='# '
+fi
diff --git a/package/petitboot/shell_profile b/package/petitboot/shell_profile
new file mode 100644
index 000000000000..1ca5e6364dba
--- /dev/null
+++ b/package/petitboot/shell_profile
@@ -0,0 +1,2 @@
+export ENV="/home/petituser/.shrc"
+exec /usr/libexec/petitboot/pb-console
-- 
2.39.3

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