cgroup: avoid pointless cred reference count bump

of->file->f_cred already holds a reference count that is stable during
the operation.

Link: https://lore.kernel.org/r/[email protected]
Reviewed-by: Jeff Layton <[email protected]>
Reviewed-by: Jens Axboe <[email protected]>
Signed-off-by: Christian Brauner <[email protected]>

Author: brauner

kernel/cgroup/cgroup.c

@@ -5216,11 +5216,11 @@ static ssize_t __cgroup_procs_write(struct kernfs_open_file *of, char *buf,
 	 * permissions using the credentials from file open to protect against
 	 * inherited fd attacks.
 	 */
-	saved_cred = override_creds(get_new_cred(of->file->f_cred));
+	saved_cred = override_creds(of->file->f_cred);
 	ret = cgroup_attach_permissions(src_cgrp, dst_cgrp,
 					of->file->f_path.dentry->d_sb,
 					threadgroup, ctx->ns);
-	put_cred(revert_creds(saved_cred));
+	revert_creds(saved_cred);
 	if (ret)
 		goto out_finish;