[openwrt/openwrt] failsafe: fix console failsafe shell

[LEDE Commits]

robimarko pushed a commit to openwrt/openwrt.git, branch main:
https://git.openwrt.org/1310e4f1aecef6c2c1b68227216ba7cc04006002

commit 1310e4f1aecef6c2c1b68227216ba7cc04006002
Author: Mark Mentovai <mark at mentovai.com>
AuthorDate: Mon Jun 6 14:53:31 2022 -0400

    failsafe: fix console failsafe shell
    
    When running a failsafe shell on a console, job control was unavailable,
    and ^C did not function correctly.
    
    This change invokes console failsafe shells via `setsid`, making them
    session leaders and allowing them to claim controlling terminals, which
    makes job control function properly. To support this, the busybox
    `setsid` utility is enabled. This has a minimal 149-byte size impact on
    a test x86_64 squashfs rootfs image.
    
    ^C was ignored in subprocesses of failsafe shells: it was not possible
    to ^C out of a program that would not exit on its own, such as many
    typical `ping` invocations. As job control was unavailable, it was not
    possible to suspend these subprocesses either, causing a hung program to
    tie up a console indefinitely, unless another means to signal the
    program was available. This was caused by SIGINT being placed at
    disposition SIG_IGN by the shell running preinit, which it did because
    the console shell was executed asynchronously with &. That disposition
    was inherited by the console shell and its subprocesses, generally
    causing ^C to have no effect.
    
    As there is no way in busybox `ash` to reset the disposition of a signal
    already ignored at shell entry, and no apparent way to avoid SIGINT
    being placed at SIG_IGN when & is used in preinit, an alternative
    construct is needed. Now, `start-stop-daemon` is used to start (-S) the
    console failsafe shell in the background (-b). This approach does not
    alter SIGINT, allowing the console shell to be started with that
    signal's handling intact, and normal ^C processing to occur.
    
    busybox `ash` has some behaviors conditional on SHLVL, and while the
    console shells ought to run at SHLVL=1, they were not by virtue of being
    started by the shell-based preinit system. Additionally, a variety of
    detritus was present in the console shell's environment, carried over
    from preinit. These conditions are corrected by running the console
    shell via `env -i` to clear the environment and establish a minimum and
    correct set of environment variables for operation, in the same manner
    as `login`. HOME is not explicitly set, because it's addressed in
    /etc/profile. For non-failsafe console shells when
    system. at system[0].ttylogin = 0, `login -f root` achieves a similar
    effect. (`login` already started non-failsafe console shells when
    ttylogin = 1 and behaved correctly. This brings the ttylogin = 0 case to
    parity.) Note that even `login -f` is somewhat undesirable for failsafe
    shells because it requires a viable /etc/passwd, hence the `env -i`
    construct in that case.
    
    The TERM environment variable from the preinit environment, with value
    "linux", would rarely be correct for serial consoles. Now, the preinit
    TERM value is preserved (or set to "linux" if unset) only when the
    console is /dev/console or /dev/tty[0-9]*. Otherwise, it will be set to
    a safe default appropriate for serial consoles, "vt102", as used for
    serial consoles by busybox init. This "linux"/"vt102" TERM setting is
    also duplicated for non-failsafe console shells.
    
    This also indicates failsafe mode by showing "- failsafe -" on all
    consoles (not just the last-defined one). It sets a hostname of
    "OpenWrt-failsafe" in failsafe mode which is rendered in the shell's
    prompt as a reminder of the mode during interactive failsafe use.
    Previously, no hostname was set, which resulted in the kernel-default
    hostname, "(none)", appearing in failsafe shell prompts.
    
    Signed-off-by: Mark Mentovai <mark at mentovai.com>
    Link: https://github.com/openwrt/openwrt/pull/16113
    Signed-off-by: Robert Marko <robimarko at gmail.com>
---
 .../base-files/files/lib/preinit/10_indicate_failsafe  |  7 ++++++-
 package/base-files/files/lib/preinit/30_failsafe_wait  |  5 ++++-
 .../base-files/files/lib/preinit/99_10_failsafe_login  | 18 +++++++++++++-----
 package/base-files/files/usr/libexec/login.sh          | 14 +++++++++++++-
 package/utils/busybox/Config-defaults.in               |  2 +-
 5 files changed, 37 insertions(+), 9 deletions(-)

diff --git a/package/base-files/files/lib/preinit/10_indicate_failsafe b/package/base-files/files/lib/preinit/10_indicate_failsafe
index 7bf5e029e4..8c950bff74 100644
--- a/package/base-files/files/lib/preinit/10_indicate_failsafe
+++ b/package/base-files/files/lib/preinit/10_indicate_failsafe
@@ -9,9 +9,14 @@ indicate_failsafe_led () {
 
 indicate_failsafe() {
 	[ "$pi_preinit_no_failsafe" = "y" ] && return
-	echo "- failsafe -"
+	local consoles="$(cat /sys/class/tty/console/active)"
+	[ -n "$consoles" ] || consoles=console
+	for console in $consoles; do
+		[ -c "/dev/$console" ] && echo "- failsafe -" >"/dev/$console"
+	done
 	preinit_net_echo "Entering Failsafe!\n"
 	indicate_failsafe_led
+	echo OpenWrt-failsafe > /proc/sys/kernel/hostname
 }
 
 boot_hook_add failsafe indicate_failsafe
diff --git a/package/base-files/files/lib/preinit/30_failsafe_wait b/package/base-files/files/lib/preinit/30_failsafe_wait
index 9ab2e8bd4d..c792089ece 100644
--- a/package/base-files/files/lib/preinit/30_failsafe_wait
+++ b/package/base-files/files/lib/preinit/30_failsafe_wait
@@ -40,7 +40,7 @@ fs_wait_for_key () {
 		rm -f $keypress_wait
 	} &
 
-	local consoles="$(sed -e 's/ /\n/g' /proc/cmdline | grep '^console=' | sed -e 's/^console=//' -e 's/,.*//')"
+	local consoles="$(cat /sys/class/tty/console/active)"
 	[ -n "$consoles" ] || consoles=console
 	for console in $consoles; do
 		[ -c "/dev/$console" ] || continue
@@ -78,6 +78,9 @@ fs_wait_for_key () {
 	keypressed=1
 	[ "$(cat $keypress_true)" = "true" ] && keypressed=0
 
+	trap - INT
+	trap - USR1
+
 	rm -f $keypress_true
 	rm -f $keypress_wait
 	rm -f $keypress_sec
diff --git a/package/base-files/files/lib/preinit/99_10_failsafe_login b/package/base-files/files/lib/preinit/99_10_failsafe_login
index 6f4af3f28b..f72a35ed53 100644
--- a/package/base-files/files/lib/preinit/99_10_failsafe_login
+++ b/package/base-files/files/lib/preinit/99_10_failsafe_login
@@ -2,14 +2,22 @@
 # Copyright (C) 2010 Vertical Communications
 
 failsafe_shell() {
-	local consoles="$(sed -e 's/ /\n/g' /proc/cmdline | grep '^console=' | sed -e 's/^console=//' -e 's/,.*//')"
+	local consoles="$(cat /sys/class/tty/console/active)"
 	[ -n "$consoles" ] || consoles=console
 	for console in $consoles; do
-		[ -c "/dev/$console" ] && while true; do
-			ash --login <"/dev/$console" >"/dev/$console" 2>"/dev/$console"
-			sleep 1
-		done &
+		case "$console" in
+			console|tty[0-9]*)
+				term=${TERM:-linux}
+				;;
+			*)
+				term=vt102
+				;;
+		esac
+		# Running asynchronously via the shell's & would ignore SIGINT,
+		# breaking ^C. Use start-stop-daemon instead.
+		[ -c "/dev/$console" ] && start-stop-daemon -Sb -p /dev/null -- env -i ash -c "while true; do setsid -c env -i USER=root LOGNAME=root SHELL=/bin/ash TERM="$term" ash --login <\"/dev/$console\" >\"/dev/$console\" 2>\"/dev/$console\"; sleep 1; done"
 	done
+
 }
 
 boot_hook_add failsafe failsafe_shell
diff --git a/package/base-files/files/usr/libexec/login.sh b/package/base-files/files/usr/libexec/login.sh
index 1fff39c6a0..e2f898e850 100755
--- a/package/base-files/files/usr/libexec/login.sh
+++ b/package/base-files/files/usr/libexec/login.sh
@@ -1,5 +1,17 @@
 #!/bin/sh
 
-[ "$(uci -q get system. at system[0].ttylogin)" = 1 ] || exec /bin/ash --login
+[ -t 0 ] && {
+	tty_dev=$(readlink /proc/self/fd/0)
+	case "$tty_dev" in
+		/dev/console|/dev/tty[0-9]*)
+			export TERM=${TERM:-linux}
+			;;
+		/dev/*)
+			export TERM=vt102
+			;;
+	esac
+}
+
+[ "$(uci -q get system. at system[0].ttylogin)" = 1 ] || exec /bin/login -f root
 
 exec /bin/login
diff --git a/package/utils/busybox/Config-defaults.in b/package/utils/busybox/Config-defaults.in
index 515bea3d1d..f88f395e2c 100644
--- a/package/utils/busybox/Config-defaults.in
+++ b/package/utils/busybox/Config-defaults.in
@@ -1801,7 +1801,7 @@ config BUSYBOX_DEFAULT_FEATURE_SETPRIV_CAPABILITY_NAMES
 	default n
 config BUSYBOX_DEFAULT_SETSID
 	bool
-	default n
+	default y
 config BUSYBOX_DEFAULT_SWAPON
 	bool
 	default y