1 // SPDX-License-Identifier: GPL-2.0 2 /* 3 * fs/sysfs/symlink.c - operations for initializing and mounting sysfs 4 * 5 * Copyright (c) 2001-3 Patrick Mochel 6 * Copyright (c) 2007 SUSE Linux Products GmbH 7 * Copyright (c) 2007 Tejun Heo <teheo@suse.de> 8 * 9 * Please see Documentation/filesystems/sysfs.rst for more information. 10 */ 11 12 #include <linux/fs.h> 13 #include <linux/magic.h> 14 #include <linux/mount.h> 15 #include <linux/init.h> 16 #include <linux/slab.h> 17 #include <linux/user_namespace.h> 18 #include <linux/fs_context.h> 19 #include <net/net_namespace.h> 20 21 #include "sysfs.h" 22 23 static struct kernfs_root *sysfs_root; 24 struct kernfs_node *sysfs_root_kn; 25 26 static void sysfs_fs_context_free(struct fs_context *fc) 27 { 28 struct kernfs_fs_context *kfc = fc->fs_private; 29 30 if (kfc->ns_tag) 31 kobj_ns_drop(KOBJ_NS_TYPE_NET, kfc->ns_tag); 32 kernfs_free_fs_context(fc); 33 kfree(kfc); 34 } 35 36 static const struct fs_context_operations sysfs_fs_context_ops = { 37 .free = sysfs_fs_context_free, 38 .get_tree = kernfs_get_tree, 39 }; 40 41 static int sysfs_init_fs_context(struct fs_context *fc) 42 { 43 struct kernfs_fs_context *kfc; 44 struct ns_common *ns; 45 46 if (!(fc->sb_flags & SB_KERNMOUNT)) { 47 if (!kobj_ns_current_may_mount(KOBJ_NS_TYPE_NET)) 48 return -EPERM; 49 } 50 51 kfc = kzalloc_obj(struct kernfs_fs_context); 52 if (!kfc) 53 return -ENOMEM; 54 55 kfc->ns_tag = ns = kobj_ns_grab_current(KOBJ_NS_TYPE_NET); 56 kfc->root = sysfs_root; 57 kfc->magic = SYSFS_MAGIC; 58 fc->fs_private = kfc; 59 fc->ops = &sysfs_fs_context_ops; 60 if (ns) { 61 struct net *netns = to_net_ns(ns); 62 63 put_user_ns(fc->user_ns); 64 fc->user_ns = get_user_ns(netns->user_ns); 65 } 66 fc->global = true; 67 return 0; 68 } 69 70 static void sysfs_kill_sb(struct super_block *sb) 71 { 72 struct ns_common *ns = (struct ns_common *)kernfs_super_ns(sb); 73 74 kernfs_kill_sb(sb); 75 kobj_ns_drop(KOBJ_NS_TYPE_NET, ns); 76 } 77 78 static struct file_system_type sysfs_fs_type = { 79 .name = "sysfs", 80 .init_fs_context = sysfs_init_fs_context, 81 .kill_sb = sysfs_kill_sb, 82 .fs_flags = FS_USERNS_MOUNT | FS_USERNS_MOUNT_RESTRICTED, 83 }; 84 85 int __init sysfs_init(void) 86 { 87 int err; 88 89 sysfs_root = kernfs_create_root(NULL, KERNFS_ROOT_EXTRA_OPEN_PERM_CHECK, 90 NULL); 91 if (IS_ERR(sysfs_root)) 92 return PTR_ERR(sysfs_root); 93 94 sysfs_root_kn = kernfs_root_to_node(sysfs_root); 95 96 err = register_filesystem(&sysfs_fs_type); 97 if (err) { 98 kernfs_destroy_root(sysfs_root); 99 return err; 100 } 101 102 return 0; 103 } 104