cgroups: rework cg_unified_init()

Cc: stable-4.0
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

diff --git a/src/lxc/cgroups/cgfsng.c b/src/lxc/cgroups/cgfsng.c
index ce8adeee6044b1ffa749b400a51a39a505b98a72..c6d05c37685b038e0d9973f2967c8391491c7a0d 100644 (file)
--- a/src/lxc/cgroups/cgfsng.c
+++ b/src/lxc/cgroups/cgfsng.c
@@ -3298,12 +3298,11 @@ static char *cg_unified_get_current_cgroup(bool relative)
 static int cg_unified_init(struct cgroup_ops *ops, bool relative,
                           bool unprivileged)
 {
-       __do_free char *subtree_path = NULL;
+       __do_close int cgroup_root_fd = -EBADF;
+       __do_free char *base_cgroup = NULL, *controllers_path = NULL;
        int ret;
-       char *mountpoint;
        char **delegatable;
        struct hierarchy *new;
-       char *base_cgroup = NULL;
 
        ret = unified_cgroup_hierarchy();
        if (ret == -ENOMEDIUM)
@@ -3318,14 +3317,18 @@ static int cg_unified_init(struct cgroup_ops *ops, bool relative,
        if (!relative)
                prune_init_scope(base_cgroup);
 
+       cgroup_root_fd = openat(-EBADF, DEFAULT_CGROUP_MOUNTPOINT,
+                               O_NOCTTY | O_CLOEXEC | O_NOFOLLOW | O_DIRECTORY);
+       if (cgroup_root_fd < 0)
+               return -errno;
+
        /*
         * We assume that the cgroup we're currently in has been delegated to
         * us and we are free to further delege all of the controllers listed
         * in cgroup.controllers further down the hierarchy.
         */
-       mountpoint = must_copy_string(DEFAULT_CGROUP_MOUNTPOINT);
-       subtree_path = must_make_path(mountpoint, base_cgroup, "cgroup.controllers", NULL);
-       delegatable = cg_unified_get_controllers(subtree_path);
+       controllers_path = must_make_path_relative(base_cgroup, "cgroup.controllers", NULL);
+       delegatable = cg_unified_get_controllers(cgroup_root_fd, controllers_path);
        if (!delegatable)
                delegatable = cg_unified_make_empty_controller();
        if (!delegatable[0])
@@ -3338,7 +3341,11 @@ static int cg_unified_init(struct cgroup_ops *ops, bool relative,
         * controllers per container.
         */
 
-       new = add_hierarchy(&ops->hierarchies, delegatable, mountpoint, base_cgroup, CGROUP2_SUPER_MAGIC);
+       new = add_hierarchy(&ops->hierarchies,
+                           delegatable,
+                           must_copy_string(DEFAULT_CGROUP_MOUNTPOINT),
+                           move_ptr(base_cgroup),
+                           CGROUP2_SUPER_MAGIC);
        if (unprivileged)
                cg_unified_delegate(&new->cgroup2_chown);