import: require force when cachefile hostid doesn't match on-disk

Previously, if a cachefile is passed to zpool import, the cached config
is mostly offered as-is to ZFS_IOC_POOL_TRYIMPORT->spa_tryimport(), and
the results are taken as the canonical pool config and handed back to
ZFS_IOC_POOL_IMPORT.

In the course of its operation, spa_load() will inspect the pool and
build a new config from what it finds on disk. However, it then
regenerates a new config ready to import, and so rightly sets the hostid
and hostname for the local host in the config it returns.

Because of this, the "require force" checks always decide the pool is
exported and last touched by the local host, even if this is not true,
which is possible in a HA environment when MMP is not enabled. The pool
may be imported on another head, but the import checks still pass here,
so the pool ends up imported on both.

(This doesn't happen when a cachefile isn't used, because the pool
config is discovered in userspace in zpool_find_import(), and that does
find the on-disk hostid and hostname correctly).

Since the systemd zfs-import-cache.service unit uses cachefile imports,
this can lead to a system returning after a crash with a "valid"
cachefile on disk and automatically, quietly, importing a pool that has
already been taken up by a secondary head.

This commit causes the on-disk hostid and hostname to be included in the
ZPOOL_CONFIG_LOAD_INFO item in the returned config, and then changes the
"force" checks for zpool import to use them if present.

This method should give no change in behaviour for old userspace on new
kernels (they won't know to look for the new config items) and for new
userspace on old kernels (the won't find the new config items).

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Rob Norris <rob.norris@klarasystems.com>
Sponsored-by: Klara, Inc.
Sponsored-by: Wasabi Technology, Inc.
Closes openzfs#15290

cmd/zpool/zpool_main.c

@@ -3122,12 +3122,21 @@ zfs_force_import_required(nvlist_t *config)
 	nvlist_t *nvinfo;
 
 	state = fnvlist_lookup_uint64(config, ZPOOL_CONFIG_POOL_STATE);
-	(void) nvlist_lookup_uint64(config, ZPOOL_CONFIG_HOSTID, &hostid);
+	nvinfo = fnvlist_lookup_nvlist(config, ZPOOL_CONFIG_LOAD_INFO);
+
+	/*
+	 * The hostid on LOAD_INFO comes from the MOS label via
+	 * spa_tryimport(). If its not there then we're likely talking to an
+	 * older kernel, so use the top one, which will be from the label
+	 * discovered in zpool_find_import(), or if a cachefile is in use, the
+	 * local hostid.
+	 */
+	if (nvlist_lookup_uint64(nvinfo, ZPOOL_CONFIG_HOSTID, &hostid) != 0)
+		nvlist_lookup_uint64(config, ZPOOL_CONFIG_HOSTID, &hostid);
 
 	if (state != POOL_STATE_EXPORTED && hostid != get_system_hostid())
 		return (B_TRUE);
 
-	nvinfo = fnvlist_lookup_nvlist(config, ZPOOL_CONFIG_LOAD_INFO);
 	if (nvlist_exists(nvinfo, ZPOOL_CONFIG_MMP_STATE)) {
 		mmp_state_t mmp_state = fnvlist_lookup_uint64(nvinfo,
 		    ZPOOL_CONFIG_MMP_STATE);
@@ -3198,15 +3207,21 @@ do_import(nvlist_t *config, const char *newname, const char *mntopts,
 			time_t timestamp = 0;
 			uint64_t hostid = 0;
 
-			if (nvlist_exists(config, ZPOOL_CONFIG_HOSTNAME))
+			if (nvlist_exists(nvinfo, ZPOOL_CONFIG_HOSTNAME))
+				hostname = fnvlist_lookup_string(nvinfo,
+				    ZPOOL_CONFIG_HOSTNAME);
+			else if (nvlist_exists(config, ZPOOL_CONFIG_HOSTNAME))
 				hostname = fnvlist_lookup_string(config,
 				    ZPOOL_CONFIG_HOSTNAME);
 
 			if (nvlist_exists(config, ZPOOL_CONFIG_TIMESTAMP))
 				timestamp = fnvlist_lookup_uint64(config,
 				    ZPOOL_CONFIG_TIMESTAMP);
 
-			if (nvlist_exists(config, ZPOOL_CONFIG_HOSTID))
+			if (nvlist_exists(nvinfo, ZPOOL_CONFIG_HOSTID))
+				hostid = fnvlist_lookup_uint64(nvinfo,
+				    ZPOOL_CONFIG_HOSTID);
+			else if (nvlist_exists(config, ZPOOL_CONFIG_HOSTID))
 				hostid = fnvlist_lookup_uint64(config,
 				    ZPOOL_CONFIG_HOSTID);
 

module/zfs/spa.c

@@ -3935,6 +3935,24 @@ spa_ld_trusted_config(spa_t *spa, spa_import_type_t type,
 	rvd = mrvd;
 	spa_config_exit(spa, SCL_ALL, FTAG);
 
+	/*
+	 * If 'zpool import' used a cached config, then the on-disk hostid and
+	 * hostname may be different to the cached config in ways that should
+	 * prevent import.  Userspace can't discover this without a scan, but
+	 * we know, so we add these values to LOAD_INFO so the caller can know
+	 * the difference.
+	 *
+	 * Note that we have to do this before the config is regenerated,
+	 * because the new config will have the hostid and hostname for this
+	 * host, in readiness for import.
+	 */
+	if (nvlist_exists(mos_config, ZPOOL_CONFIG_HOSTID))
+		fnvlist_add_uint64(spa->spa_load_info, ZPOOL_CONFIG_HOSTID,
+		    fnvlist_lookup_uint64(mos_config, ZPOOL_CONFIG_HOSTID));
+	if (nvlist_exists(mos_config, ZPOOL_CONFIG_HOSTNAME))
+		fnvlist_add_string(spa->spa_load_info, ZPOOL_CONFIG_HOSTNAME,
+		    fnvlist_lookup_string(mos_config, ZPOOL_CONFIG_HOSTNAME));
+
 	/*
 	 * We will use spa_config if we decide to reload the spa or if spa_load
 	 * fails and we rewind. We must thus regenerate the config using the

tests/zfs-tests/tests/functional/cli_root/zpool_import/zpool_import_hostid_changed_cachefile_unclean_export.ksh

@@ -20,8 +20,8 @@
 
 #
 # DESCRIPTION:
-# A pool that wasn't cleanly exported should be importable from a cachefile
-# without force even if the local hostid doesn't match the on-disk hostid.
+# A pool that wasn't cleanly exported should not be importable from a cachefile
+# without force if the local hostid doesn't match the on-disk hostid.
 #
 # STRATEGY:
 #	1. Set a hostid.
@@ -32,8 +32,9 @@
 #	4.2. Export the pool.
 #	4.3. Restore the device state from the copy.
 #	5. Change the hostid.
-#	6. Verify that importing the pool from the cachefile succeeds
-#	   without force.
+#	6. Verify that importing the pool from the cachefile fails.
+#	7. Verify that importing the pool from the cachefile with force
+#	   succeeds.
 #
 
 verify_runnable "global"
@@ -64,8 +65,11 @@ log_must rm -f $VDEV0.bak
 # 5. Change the hostid.
 log_must zgenhostid -f $HOSTID2
 
-# 6. Verify that importing the pool from the cachefile succeeds without force.
-log_must zpool import -c $CPATHBKP $TESTPOOL1
+# 6. Verify that importing the pool from the cachefile fails.
+log_mustnot zpool import -c $CPATHBKP $TESTPOOL1
 
-log_pass "zpool import can import pool from cachefile if not cleanly " \
-    "exported when hostid changes."
+# 7. Verify that importing the pool from the cachefile with force succeeds.
+log_must zpool import -f -c $CPATHBKP $TESTPOOL1
+
+log_pass "zpool import from cachefile requires force if not cleanly " \
+    "exported and hostid changes."