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 int sysfs_get_tree(struct fs_context *fc) 27 { 28 struct kernfs_fs_context *kfc = fc->fs_private; 29 int ret; 30 31 ret = kernfs_get_tree(fc); 32 if (ret) 33 return ret; 34 35 if (kfc->new_sb_created) 36 fc->root->d_sb->s_iflags |= SB_I_USERNS_VISIBLE; 37 return 0; 38 } 39 40 static void sysfs_fs_context_free(struct fs_context *fc) 41 { 42 struct kernfs_fs_context *kfc = fc->fs_private; 43 44 if (kfc->ns_tag) 45 kobj_ns_drop(KOBJ_NS_TYPE_NET, kfc->ns_tag); 46 kernfs_free_fs_context(fc); 47 kfree(kfc); 48 } 49 50 static const struct fs_context_operations sysfs_fs_context_ops = { 51 .free = sysfs_fs_context_free, 52 .get_tree = sysfs_get_tree, 53 }; 54 55 static int sysfs_init_fs_context(struct fs_context *fc) 56 { 57 struct kernfs_fs_context *kfc; 58 struct net *netns; 59 60 if (!(fc->sb_flags & SB_KERNMOUNT)) { 61 if (!kobj_ns_current_may_mount(KOBJ_NS_TYPE_NET)) 62 return -EPERM; 63 } 64 65 kfc = kzalloc(sizeof(struct kernfs_fs_context), GFP_KERNEL); 66 if (!kfc) 67 return -ENOMEM; 68 69 kfc->ns_tag = netns = kobj_ns_grab_current(KOBJ_NS_TYPE_NET); 70 kfc->root = sysfs_root; 71 kfc->magic = SYSFS_MAGIC; 72 fc->fs_private = kfc; 73 fc->ops = &sysfs_fs_context_ops; 74 if (netns) { 75 put_user_ns(fc->user_ns); 76 fc->user_ns = get_user_ns(netns->user_ns); 77 } 78 fc->global = true; 79 return 0; 80 } 81 82 static void sysfs_kill_sb(struct super_block *sb) 83 { 84 void *ns = (void *)kernfs_super_ns(sb); 85 86 kernfs_kill_sb(sb); 87 kobj_ns_drop(KOBJ_NS_TYPE_NET, ns); 88 } 89 90 static struct file_system_type sysfs_fs_type = { 91 .name = "sysfs", 92 .init_fs_context = sysfs_init_fs_context, 93 .kill_sb = sysfs_kill_sb, 94 .fs_flags = FS_USERNS_MOUNT, 95 }; 96 97 int __init sysfs_init(void) 98 { 99 int err; 100 101 sysfs_root = kernfs_create_root(NULL, KERNFS_ROOT_EXTRA_OPEN_PERM_CHECK, 102 NULL); 103 if (IS_ERR(sysfs_root)) 104 return PTR_ERR(sysfs_root); 105 106 sysfs_root_kn = sysfs_root->kn; 107 108 err = register_filesystem(&sysfs_fs_type); 109 if (err) { 110 kernfs_destroy_root(sysfs_root); 111 return err; 112 } 113 114 return 0; 115 } 116