[PATCH] dnsmasq: procd-ujail: workaround startup failure, when leasefile location is in /tmp

[Bastian Bittorf]

introduced with 44f694ba1bca1417d24e851c637c284f9f78c06d
("build: select procd-ujail if !SMALL_FLASH") dnsmasq fails
to startup when the leasefile is configured to be in /tmp,
which is just not suited for beeing a jail location.

Workaround this (no jailing for this file for this special case)
and show a proper information in syslog.

without this patch, the syslog shows:
Thu Oct 14 18:32:38 2021 user.err : jail: creat(/tmp/ujail-lhNbFK/tmp/dhcp.leases) failed: Read-only file system
Thu Oct 14 18:32:38 2021 daemon.crit dnsmasq[1]: cannot open or create lease file /tmp/dhcp.leases: Read-only file system
Thu Oct 14 18:32:38 2021 daemon.crit dnsmasq[1]: FAILED to start up

Ref: https://bugs.openwrt.org/index.php?do=details&task_id=4085
Acked-by: Daniel Golle <daniel at makrotopia.org>
Signed-off-by: Bastian Bittorf <bb at npl.de>
---
 .../services/dnsmasq/files/dnsmasq.init       | 19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/package/network/services/dnsmasq/files/dnsmasq.init b/package/network/services/dnsmasq/files/dnsmasq.init
index 3250b2179b..af2effdb26 100644
--- a/package/network/services/dnsmasq/files/dnsmasq.init
+++ b/package/network/services/dnsmasq/files/dnsmasq.init
@@ -616,7 +616,7 @@ dhcp_add() {
 
 		case $ra_management in
 		0)
-			# SLACC with DCHP for extended options
+			# SLACC with DHCP for extended options
 			xappend "--dhcp-range=$nettag::,constructor:$ifname,ra-stateless,ra-names"
 			;;
 		2)
@@ -816,7 +816,7 @@ dnsmasq_start()
 {
 	local cfg="$1"
 	local disabled user_dhcpscript
-	local resolvfile resolvdir localuse=0
+	local resolvfile resolvdir leasedir localuse=0
 
 	config_get_bool disabled "$cfg" disabled 0
 	[ "$disabled" -gt 0 ] && return 0
@@ -994,7 +994,11 @@ dnsmasq_start()
 	fi
 
 	config_get leasefile $cfg leasefile "/tmp/dhcp.leases"
-	[ -n "$leasefile" ] && [ ! -e "$leasefile" ] && touch "$leasefile"
+	[ -n "$leasefile" ] && {
+		leasedir="$( dirname "$leasefile" )" && mkdir -p "$leasedir"
+		[ ! -e "$leasefile" ] && touch "$leasefile"
+	}
+
 	config_get_bool cachelocal "$cfg" cachelocal 1
 
 	config_get_bool noresolv "$cfg" noresolv 0
@@ -1154,6 +1158,15 @@ dnsmasq_start()
 	procd_add_jail_mount $EXTRA_MOUNT $RFC6761FILE $TRUSTANCHORSFILE
 	procd_add_jail_mount $dnsmasqconffile $dnsmasqconfdir $resolvdir $user_dhcpscript
 	procd_add_jail_mount /etc/passwd /etc/group /etc/TZ /etc/hosts /etc/ethers
+
+	[ -d "$leasedir" ] && {
+		[ "$leasedir" = '/tmp' ] && {
+			logger -t dnsmasq \
+				"consider using a more private directory for leasefile" \
+				"because jailing /tmp does not work: choose e.g. /tmp/dnsmasq/leasefile"
+		}
+		procd_add_jail_mount_rw $leasedir
+	}
 	procd_add_jail_mount_rw /var/run/dnsmasq/ $leasefile
 
 	procd_close_instance
-- 
2.30.2