tests: Add mount propagation test

This tests the current behavior of making /sysroot a private mount so
that submounts on /var do not propagate back to /sysroot. It also shows
how submounts of /sysroot do not propagate into separate mount
namespaces for the same reason.

tests/kolainst/destructive/mount-propagation.sh

@@ -0,0 +1,141 @@
+#!/bin/bash
+# https://bugzilla.redhat.com/show_bug.cgi?id=1498281
+set -xeuo pipefail
+
+. ${KOLA_EXT_DATA}/libinsttest.sh
+
+require_writable_sysroot
+
+get_mount() {
+  local target=${1:?No target specified}
+  local pid=${2:?No PID specified}
+
+  # findmnt always looks at /proc/self/mountinfo, so we have to first enter the
+  # mount namespace of the desired process.
+  nsenter --target "${pid}" --mount -- \
+      findmnt --json --list --output +PROPAGATION,OPT-FIELDS \
+      | jq ".filesystems[] | select(.target == \"${target}\")"
+}
+
+assert_has_mount() {
+  local target=${1:?No target specified}
+  local pid=${2:-$$}
+  local mount
+
+  mount=$(get_mount "${target}" "${pid}")
+  if [ -n "${mount}" ]; then
+    echo -e "Process ${pid} has mount '${target}':\n${mount}"
+  else
+    cat "/proc/${pid}/mountinfo" >&2
+    fatal "Mount '${target}' not found in process ${pid}"
+  fi
+}
+
+assert_not_has_mount() {
+  local target=${1:?No target specified}
+  local pid=${2:-$$}
+  local mount
+
+  mount=$(get_mount "${target}" "${pid}")
+  if [ -n "${mount}" ]; then
+    cat "/proc/${pid}/mountinfo" >&2
+    fatal "Mount '${target}' found in process ${pid}"
+  else
+    echo "Process ${pid} does not have mount '${target}'"
+  fi
+}
+
+test_mounts() {
+  local stateroot
+
+  echo "Root namespace mountinfo:"
+  cat "/proc/$$/mountinfo"
+
+  echo "Sub namespace mountinfo:"
+  cat "/proc/${ns_pid}/mountinfo"
+
+  # Make sure the 2 PIDs are really in different mount namespaces.
+  root_ns=$(readlink "/proc/$$/ns/mnt")
+  sub_ns=$(readlink "/proc/${ns_pid}/ns/mnt")
+  assert_not_streq "${root_ns}" "${sub_ns}"
+
+  stateroot=$(rpmostree_query_json '.deployments[0].osname')
+
+  # Check the mounts exist in the root namespace and the /var/foo mount has not
+  # propagated back to /sysroot.
+  assert_has_mount /var/foo
+  assert_has_mount /sysroot/bar
+  assert_not_has_mount "/sysroot/ostree/deploy/${stateroot}/var/foo"
+
+  # Repeat with the sub mount namespace. Since /sysroot is marked private,
+  # /sysroot/bar will not be propagated into it.
+  assert_has_mount /var/foo "${ns_pid}"
+  assert_not_has_mount /sysroot/bar "${ns_pid}"
+  assert_not_has_mount "/sysroot/ostree/deploy/${stateroot}/var/foo" "${ns_pid}"
+}
+
+case "${AUTOPKGTEST_REBOOT_MARK:-}" in
+  "")
+    mkdir -p /var/foo /sysroot/bar
+
+    # Create a process in a separate mount namespace to see if the mounts
+    # propagate into it correctly.
+    unshare -m --propagation unchanged -- sleep infinity &
+    ns_pid=$!
+
+    mount -t tmpfs foo /var/foo
+    mount -t tmpfs bar /sysroot/bar
+
+    test_mounts
+
+    # Now setup for the same test but with the mounts made early via fstab.
+    cat >> /etc/fstab <<"EOF"
+foo /var/foo tmpfs defaults 0 0
+bar /sysroot/bar tmpfs defaults 0 0
+EOF
+
+    # We want to start a process in a separate namespace after ostree-remount
+    # has completed but before systemd starts the fstab generated mount units.
+    cat > /etc/systemd/system/test-mounts.service <<"EOF"
+[Unit]
+DefaultDependencies=no
+After=ostree-remount.service
+Before=var-foo.mount sysroot-bar.mount
+RequiresMountsFor=/var /sysroot
+Conflicts=shutdown.target
+Before=shutdown.target
+
+[Service]
+Type=exec
+ExecStart=/usr/bin/sleep infinity
+ProtectSystem=strict
+
+[Install]
+WantedBy=local-fs.target
+EOF
+    systemctl enable test-mounts.service
+
+    /tmp/autopkgtest-reboot 2
+    ;;
+  2)
+    # Check that the test service is running and get its PID.
+    ns_state=$(systemctl show -P ActiveState test-mounts.service)
+    assert_streq "${ns_state}" active
+    ns_pid=$(systemctl show -P MainPID test-mounts.service)
+
+    # Make sure that test-mounts.service started after ostree-remount.service
+    # but before /var/foo and /sysroot/bar were mounted so that we can see if
+    # the mounts were propagated into its mount namespace.
+    remount_finished=$(journalctl -o json -g Finished -u ostree-remount.service | tail -n1 | jq -r .__MONOTONIC_TIMESTAMP)
+    test_starting=$(journalctl -o json -g Starting -u test-mounts.service | tail -n1 | jq -r .__MONOTONIC_TIMESTAMP)
+    test_started=$(journalctl -o json -g Started -u test-mounts.service | tail -n1 | jq -r .__MONOTONIC_TIMESTAMP)
+    foo_mounting=$(journalctl -o json -g Mounting -u var-foo.mount | tail -n1 | jq -r .__MONOTONIC_TIMESTAMP)
+    bar_mounting=$(journalctl -o json -g Mounting -u sysroot-bar.mount | tail -n1 | jq -r .__MONOTONIC_TIMESTAMP)
+    test "${remount_finished}" -lt "${test_starting}"
+    test "${test_started}" -lt "${foo_mounting}"
+    test "${test_started}" -lt "${bar_mounting}"
+
+    test_mounts
+    ;;
+  *) fatal "Unexpected AUTOPKGTEST_REBOOT_MARK=${AUTOPKGTEST_REBOOT_MARK}" ;;
+esac