cr-check: fill up a root task mount namespace

A root mount namespace list is used to resolve paths to
unix sockets if they are placed on btrfs.

This patch fixes a crash:
 #0 mount_resolve_path at criu/mount.c:213
 #1 phys_stat_resolve_dev at criu/mount.c:240
 #2 phys_stat_dev_match at criu/mount.c:256
 checkpoint-restore#3 unix_process_name at criu/sk-unix.c:565
 checkpoint-restore#4 unix_collect_one at criu/sk-unix.c:620
 checkpoint-restore#5 unix_receive_one at criu/sk-unix.c:692
 checkpoint-restore#6 nlmsg_receive at criu/libnetlink.c:45
 checkpoint-restore#7 do_rtnl_req at criu/libnetlink.c:119
 checkpoint-restore#8 do_collect_req at criu/sockets.c:610
 checkpoint-restore#9 collect_sockets at criu/sockets.c:636

https://bugzilla.redhat.com/show_bug.cgi?id=1381351
Signed-off-by: Andrei Vagin <[email protected]>

Author: avagin

criu/cr-check.c

@@ -1017,7 +1017,7 @@ static int (*chk_feature)(void);
 			} while (0)
 int cr_check(void)
 {
-	struct ns_id ns = { .type = NS_CRIU, .ns_pid = PROC_SELF, .nd = &mnt_ns_desc };
+	struct ns_id *ns;
 	int ret = 0;
 
 	if (!is_root_user())
@@ -1032,9 +1032,11 @@ int cr_check(void)
 	if (collect_pstree_ids())
 		return -1;
 
-	ns.id = root_item->ids->mnt_ns_id;
+	ns = lookup_ns_by_id(root_item->ids->mnt_ns_id, &mnt_ns_desc);
+	if (ns == NULL)
+		return -1;
 
-	mntinfo = collect_mntinfo(&ns, false);
+	mntinfo = collect_mntinfo(ns, false);
 	if (mntinfo == NULL)
 		return -1;