kernel/cgroup: use kernfs_create_dir_ns()

By passing the fsugid to kernfs_create_dir_ns(), we don't need
cgroup_kn_set_ugid() any longer.  That function was added for exactly
this purpose by commit 49957f8e2a43 ("cgroup: newly created dirs and
files should be owned by the creator").

Eliminating this piece of duplicate code means we benefit from future
improvements to kernfs_create_dir_ns(); for example, both are lacking
S_ISGID support currently, which my next patch will add to
kernfs_create_dir_ns().  It cannot (easily) be added to
cgroup_kn_set_ugid() because we can't dereference struct kernfs_iattrs
from there.

--
v1 -> v2: 12-digit commit id

Signed-off-by: Max Kellermann <max.kellermann@ionos.com>
Acked-by: Tejun Heo <tj@kernel.org>
Link: https://lore.kernel.org/r/20231208093310.297233-1-max.kellermann@ionos.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 4b9ff41ca603a3a9952d079b3180b43474b9f892..a844b421fd83fc0b9c8388e6f051ad1d77c3fb94 100644 (file)
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -4169,20 +4169,6 @@ static struct kernfs_ops cgroup_kf_ops = {
        .seq_show               = cgroup_seqfile_show,
 };
 
-/* set uid and gid of cgroup dirs and files to that of the creator */
-static int cgroup_kn_set_ugid(struct kernfs_node *kn)
-{
-       struct iattr iattr = { .ia_valid = ATTR_UID | ATTR_GID,
-                              .ia_uid = current_fsuid(),
-                              .ia_gid = current_fsgid(), };
-
-       if (uid_eq(iattr.ia_uid, GLOBAL_ROOT_UID) &&
-           gid_eq(iattr.ia_gid, GLOBAL_ROOT_GID))
-               return 0;
-
-       return kernfs_setattr(kn, &iattr);
-}
-
 static void cgroup_file_notify_timer(struct timer_list *timer)
 {
        cgroup_file_notify(container_of(timer, struct cgroup_file,
@@ -4195,25 +4181,18 @@ static int cgroup_add_file(struct cgroup_subsys_state *css, struct cgroup *cgrp,
        char name[CGROUP_FILE_NAME_MAX];
        struct kernfs_node *kn;
        struct lock_class_key *key = NULL;
-       int ret;
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
        key = &cft->lockdep_key;
 #endif
        kn = __kernfs_create_file(cgrp->kn, cgroup_file_name(cgrp, cft, name),
                                  cgroup_file_mode(cft),
-                                 GLOBAL_ROOT_UID, GLOBAL_ROOT_GID,
+                                 current_fsuid(), current_fsgid(),
                                  0, cft->kf_ops, cft,
                                  NULL, key);
        if (IS_ERR(kn))
                return PTR_ERR(kn);
 
-       ret = cgroup_kn_set_ugid(kn);
-       if (ret) {
-               kernfs_remove(kn);
-               return ret;
-       }
-
        if (cft->file_offset) {
                struct cgroup_file *cfile = (void *)css + cft->file_offset;
 
@@ -5616,7 +5595,9 @@ static struct cgroup *cgroup_create(struct cgroup *parent, const char *name,
                goto out_cancel_ref;
 
        /* create the directory */
-       kn = kernfs_create_dir(parent->kn, name, mode, cgrp);
+       kn = kernfs_create_dir_ns(parent->kn, name, mode,
+                                 current_fsuid(), current_fsgid(),
+                                 cgrp, NULL);
        if (IS_ERR(kn)) {
                ret = PTR_ERR(kn);
                goto out_stat_exit;
@@ -5761,10 +5742,6 @@ int cgroup_mkdir(struct kernfs_node *parent_kn, const char *name, umode_t mode)
         */
        kernfs_get(cgrp->kn);
 
-       ret = cgroup_kn_set_ugid(cgrp->kn);
-       if (ret)
-               goto out_destroy;
-
        ret = css_populate_dir(&cgrp->self);
        if (ret)
                goto out_destroy;