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Harden monit-access-helper.sh cgroupv2 mount point detection #599

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Harden monit-access-helper.sh cgroupv2 mount point detection #599

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1e4a114
Harden monit-access-helper.sh cgroupv2 mount point detection
gberche-orange May 7, 2026
50cc4d1
Refine error message when cgroupsv2 mount or path are not resolved
gberche-orange May 13, 2026
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11 changes: 6 additions & 5 deletions stemcell_builder/stages/bosh_monit/assets/monit-access-helper.sh
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Original file line number Diff line number Diff line change
Expand Up @@ -19,20 +19,21 @@ monit_isolation_classid=2958295041
#
# Prefer cgroup.controllers; also accept stat(2) filesystem type for hosts where
# the file is missing from the mount view but the root is still cgroup2fs.
monit_using_unified_cgroup_v2() {
system_using_unified_cgroup_v2() {
[ -f /sys/fs/cgroup/cgroup.controllers ] && return 0
[ "$(stat -fc %T /sys/fs/cgroup 2>/dev/null)" = "cgroup2fs" ]
}

permit_monit_access() {
if monit_using_unified_cgroup_v2; then
if system_using_unified_cgroup_v2; then
# cgroupv2 (unified hierarchy)
# Create a sub-cgroup under the current process's cgroup and move into it.
# The iptables rules match on this cgroup path.
cgroup_mount="$(awk '$3 == "cgroup2" { print $2 }' /proc/self/mounts)"
cgroup_mount="$(awk '$1 == "cgroup2" && $3 == "cgroup2" { print $2 }' /proc/self/mounts)"
nb_matching_cgroup_mounts=$(echo "$cgroup_mount" | wc -l)
current_cgroup="$(grep '^0::' /proc/self/cgroup | cut -d: -f3)"
if [ -z "${cgroup_mount}" ] || [ -z "${current_cgroup}" ]; then
echo "permit_monit_access: unable to resolve cgroup v2 mount or path" >&2
if [ -z "${cgroup_mount}" ] || [ "${nb_matching_cgroup_mounts}" -ne 1 ] || [ -z "${current_cgroup}" ]; then
echo "permit_monit_access: unable to resolve cgroup v2 mount or path. current_cgroup=${current_cgroup} cgroup_mount=${cgroup_mount}" >&2
return 1
fi
monit_access_cgroup="${cgroup_mount}${current_cgroup}/monit-api-access"
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