From: Reza Arbab <arbab@linux.ibm.com>
To: buildroot@buildroot.org
Date: Wed, 15 Nov 2023 15:59:31 -0600
Message-Id: <20231115215931.860940-6-arbab@linux.ibm.com>
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Subject: [Buildroot] [PATCH v4 5/5] package/petitboot: run UI as non-root
 user
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Cc: Laurent Vivier <laurent@vivier.eu>, Joel Stanley <joel@jms.id.au>
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Though the petitboot UI is a user application, it is currently being
run by root only because we use getty to display it on the console.

Create an unprivileged user to run the UI instead. The unix socket the
pb-discover daemon sets up is accessible to "petitgroup", so that should
be the gid, with arbitrary uid "petituser" to match.

This is currently the chain of processes leading to the UI:

1. /etc/init.d/pb-console start console
2. /usr/libexec/petitboot/pb-console --getty --detach -- -n -i 0 console linux
3. /sbin/getty -l/usr/libexec/petitboot/pb-console -n -i 0 console linux
4. /usr/libexec/petitboot/pb-console
5. /usr/sbin/petitboot-nc

Instead of (3) running the pb-console helper directly with "getty -l",
we can use "agetty -a" to autologin petituser, and run pb-console via
petituser's login shell:

1. /etc/init.d/pb-console start console
2. /usr/libexec/petitboot/pb-console --getty=/sbin/agetty --detach -- -a petituser -n -i console linux
3. /sbin/agetty -a petituser -n -i console linux
4. /home/petituser/.profile
5. /usr/libexec/petitboot/pb-console
6. /usr/sbin/petiboot-nc

Here, everything from (4) down is running as petituser. In (4), use
$PPID to determine if we're logging in via getty, so that logging in by
other means will give a normal 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   | 6 ++++++
 package/petitboot/shell_profile  | 3 +++
 5 files changed, 17 insertions(+), 3 deletions(-)
 create mode 100644 package/petitboot/shell_profile

diff --git a/package/petitboot/Config.in b/package/petitboot/Config.in
index 46327903ed2e..b17ce3253b74 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_PACKAGE_KEXEC_LITE_ARCH_SUPPORTS && !BR2_PACKAGE_KEXEC
 	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..9e8f6c87f8bb 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 petituser: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..8b23b2233dee 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 petituser: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 3d29d103b518..929e0574f6f9 100644
--- a/package/petitboot/petitboot.mk
+++ b/package/petitboot/petitboot.mk
@@ -76,6 +76,8 @@ define PETITBOOT_POST_INSTALL
 		$(TARGET_DIR)/etc/init.d/pb-console
 	$(INSTALL) -D -m 0755 $(PETITBOOT_PKGDIR)/pb-shell \
 		$(TARGET_DIR)/usr/libexec/petitboot/pb-shell
+	$(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 \
@@ -89,4 +91,8 @@ endef
 
 PETITBOOT_POST_INSTALL_TARGET_HOOKS += PETITBOOT_POST_INSTALL
 
+define PETITBOOT_USERS
+	petituser -1 petitgroup -1 * /home/petituser /bin/sh - petitboot user
+endef
+
 $(eval $(autotools-package))
diff --git a/package/petitboot/shell_profile b/package/petitboot/shell_profile
new file mode 100644
index 000000000000..a958ca4402f2
--- /dev/null
+++ b/package/petitboot/shell_profile
@@ -0,0 +1,3 @@
+if [ "$PPID" = "1" ]; then
+	exec /usr/libexec/petitboot/pb-console
+fi
-- 
2.39.3

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