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32 results

mlock.c

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  • proc_sysctl.c 41.01 KiB
    // SPDX-License-Identifier: GPL-2.0
    /*
     * /proc/sys support
     */
    #include <linux/init.h>
    #include <linux/sysctl.h>
    #include <linux/poll.h>
    #include <linux/proc_fs.h>
    #include <linux/printk.h>
    #include <linux/security.h>
    #include <linux/sched.h>
    #include <linux/cred.h>
    #include <linux/namei.h>
    #include <linux/mm.h>
    #include <linux/module.h>
    #include "internal.h"
    
    static const struct dentry_operations proc_sys_dentry_operations;
    static const struct file_operations proc_sys_file_operations;
    static const struct inode_operations proc_sys_inode_operations;
    static const struct file_operations proc_sys_dir_file_operations;
    static const struct inode_operations proc_sys_dir_operations;
    
    /* Support for permanently empty directories */
    
    struct ctl_table sysctl_mount_point[] = {
    	{ }
    };
    
    static bool is_empty_dir(struct ctl_table_header *head)
    {
    	return head->ctl_table[0].child == sysctl_mount_point;
    }
    
    static void set_empty_dir(struct ctl_dir *dir)
    {
    	dir->header.ctl_table[0].child = sysctl_mount_point;
    }
    
    static void clear_empty_dir(struct ctl_dir *dir)
    
    {
    	dir->header.ctl_table[0].child = NULL;
    }
    
    void proc_sys_poll_notify(struct ctl_table_poll *poll)
    {
    	if (!poll)
    		return;
    
    	atomic_inc(&poll->event);
    	wake_up_interruptible(&poll->wait);
    }
    
    static struct ctl_table root_table[] = {
    	{
    		.procname = "",
    		.mode = S_IFDIR|S_IRUGO|S_IXUGO,
    	},
    	{ }
    };
    static struct ctl_table_root sysctl_table_root = {
    	.default_set.dir.header = {
    		{{.count = 1,
    		  .nreg = 1,
    		  .ctl_table = root_table }},
    		.ctl_table_arg = root_table,
    		.root = &sysctl_table_root,
    		.set = &sysctl_table_root.default_set,
    	},
    };
    
    static DEFINE_SPINLOCK(sysctl_lock);
    
    static void drop_sysctl_table(struct ctl_table_header *header);
    static int sysctl_follow_link(struct ctl_table_header **phead,
    	struct ctl_table **pentry);
    static int insert_links(struct ctl_table_header *head);
    static void put_links(struct ctl_table_header *header);
    
    static void sysctl_print_dir(struct ctl_dir *dir)
    {
    	if (dir->header.parent)
    		sysctl_print_dir(dir->header.parent);
    	pr_cont("%s/", dir->header.ctl_table[0].procname);
    }
    
    static int namecmp(const char *name1, int len1, const char *name2, int len2)
    {
    	int minlen;
    	int cmp;
    
    	minlen = len1;
    	if (minlen > len2)
    		minlen = len2;
    
    	cmp = memcmp(name1, name2, minlen);
    	if (cmp == 0)
    		cmp = len1 - len2;
    	return cmp;
    }
    
    /* Called under sysctl_lock */
    static struct ctl_table *find_entry(struct ctl_table_header **phead,
    	struct ctl_dir *dir, const char *name, int namelen)
    {
    	struct ctl_table_header *head;
    	struct ctl_table *entry;
    	struct rb_node *node = dir->root.rb_node;
    
    	while (node)
    	{
    		struct ctl_node *ctl_node;
    		const char *procname;
    		int cmp;
    
    		ctl_node = rb_entry(node, struct ctl_node, node);
    		head = ctl_node->header;
    		entry = &head->ctl_table[ctl_node - head->node];
    		procname = entry->procname;
    
    		cmp = namecmp(name, namelen, procname, strlen(procname));
    		if (cmp < 0)
    			node = node->rb_left;
    		else if (cmp > 0)
    			node = node->rb_right;
    		else {
    			*phead = head;
    			return entry;
    		}
    	}
    	return NULL;
    }
    
    static int insert_entry(struct ctl_table_header *head, struct ctl_table *entry)
    {
    	struct rb_node *node = &head->node[entry - head->ctl_table].node;
    	struct rb_node **p = &head->parent->root.rb_node;
    	struct rb_node *parent = NULL;
    	const char *name = entry->procname;
    	int namelen = strlen(name);
    
    	while (*p) {
    		struct ctl_table_header *parent_head;
    		struct ctl_table *parent_entry;
    		struct ctl_node *parent_node;
    		const char *parent_name;
    		int cmp;
    
    		parent = *p;
    		parent_node = rb_entry(parent, struct ctl_node, node);
    		parent_head = parent_node->header;
    		parent_entry = &parent_head->ctl_table[parent_node - parent_head->node];
    		parent_name = parent_entry->procname;
    
    		cmp = namecmp(name, namelen, parent_name, strlen(parent_name));
    		if (cmp < 0)
    			p = &(*p)->rb_left;
    		else if (cmp > 0)
    			p = &(*p)->rb_right;
    		else {
    			pr_err("sysctl duplicate entry: ");
    			sysctl_print_dir(head->parent);
    			pr_cont("/%s\n", entry->procname);
    			return -EEXIST;
    		}
    	}
    
    	rb_link_node(node, parent, p);
    	rb_insert_color(node, &head->parent->root);
    	return 0;
    }
    
    static void erase_entry(struct ctl_table_header *head, struct ctl_table *entry)
    {
    	struct rb_node *node = &head->node[entry - head->ctl_table].node;
    
    	rb_erase(node, &head->parent->root);
    }
    
    static void init_header(struct ctl_table_header *head,
    	struct ctl_table_root *root, struct ctl_table_set *set,
    	struct ctl_node *node, struct ctl_table *table)
    {
    	head->ctl_table = table;
    	head->ctl_table_arg = table;
    	head->used = 0;
    	head->count = 1;
    	head->nreg = 1;
    	head->unregistering = NULL;
    	head->root = root;
    	head->set = set;
    	head->parent = NULL;
    	head->node = node;
    	INIT_HLIST_HEAD(&head->inodes);
    	if (node) {
    		struct ctl_table *entry;
    		for (entry = table; entry->procname; entry++, node++)
    			node->header = head;
    	}
    }
    
    static void erase_header(struct ctl_table_header *head)
    {
    	struct ctl_table *entry;
    	for (entry = head->ctl_table; entry->procname; entry++)
    		erase_entry(head, entry);
    }
    
    static int insert_header(struct ctl_dir *dir, struct ctl_table_header *header)
    {
    	struct ctl_table *entry;
    	int err;
    
    	/* Is this a permanently empty directory? */
    	if (is_empty_dir(&dir->header))
    		return -EROFS;
    
    	/* Am I creating a permanently empty directory? */
    	if (header->ctl_table == sysctl_mount_point) {
    		if (!RB_EMPTY_ROOT(&dir->root))
    			return -EINVAL;
    		set_empty_dir(dir);
    	}
    
    	dir->header.nreg++;
    	header->parent = dir;
    	err = insert_links(header);
    	if (err)
    		goto fail_links;
    	for (entry = header->ctl_table; entry->procname; entry++) {
    		err = insert_entry(header, entry);
    		if (err)
    			goto fail;
    	}
    	return 0;
    fail:
    	erase_header(header);
    	put_links(header);
    fail_links:
    	if (header->ctl_table == sysctl_mount_point)
    		clear_empty_dir(dir);
    	header->parent = NULL;
    	drop_sysctl_table(&dir->header);
    	return err;
    }
    
    /* called under sysctl_lock */
    static int use_table(struct ctl_table_header *p)
    {
    	if (unlikely(p->unregistering))
    		return 0;
    	p->used++;
    	return 1;
    }
    
    /* called under sysctl_lock */
    static void unuse_table(struct ctl_table_header *p)
    {
    	if (!--p->used)
    		if (unlikely(p->unregistering))
    			complete(p->unregistering);
    }
    
    static void proc_sys_prune_dcache(struct ctl_table_header *head)
    {
    	struct inode *inode;
    	struct proc_inode *ei;
    	struct hlist_node *node;
    	struct super_block *sb;
    
    	rcu_read_lock();
    	for (;;) {
    		node = hlist_first_rcu(&head->inodes);
    		if (!node)
    			break;
    		ei = hlist_entry(node, struct proc_inode, sysctl_inodes);
    		spin_lock(&sysctl_lock);
    		hlist_del_init_rcu(&ei->sysctl_inodes);
    		spin_unlock(&sysctl_lock);
    
    		inode = &ei->vfs_inode;
    		sb = inode->i_sb;
    		if (!atomic_inc_not_zero(&sb->s_active))
    			continue;
    		inode = igrab(inode);
    		rcu_read_unlock();
    		if (unlikely(!inode)) {
    			deactivate_super(sb);
    			rcu_read_lock();
    			continue;
    		}
    
    		d_prune_aliases(inode);
    		iput(inode);
    		deactivate_super(sb);
    
    		rcu_read_lock();
    	}
    	rcu_read_unlock();
    }
    
    /* called under sysctl_lock, will reacquire if has to wait */
    static void start_unregistering(struct ctl_table_header *p)
    {
    	/*
    	 * if p->used is 0, nobody will ever touch that entry again;
    	 * we'll eliminate all paths to it before dropping sysctl_lock
    	 */
    	if (unlikely(p->used)) {
    		struct completion wait;
    		init_completion(&wait);
    		p->unregistering = &wait;
    		spin_unlock(&sysctl_lock);
    		wait_for_completion(&wait);
    	} else {
    		/* anything non-NULL; we'll never dereference it */
    		p->unregistering = ERR_PTR(-EINVAL);
    		spin_unlock(&sysctl_lock);
    	}
    	/*
    	 * Prune dentries for unregistered sysctls: namespaced sysctls
    	 * can have duplicate names and contaminate dcache very badly.
    	 */
    	proc_sys_prune_dcache(p);
    	/*
    	 * do not remove from the list until nobody holds it; walking the
    	 * list in do_sysctl() relies on that.
    	 */
    	spin_lock(&sysctl_lock);
    	erase_header(p);
    }
    
    static struct ctl_table_header *sysctl_head_grab(struct ctl_table_header *head)
    {
    	BUG_ON(!head);
    	spin_lock(&sysctl_lock);
    	if (!use_table(head))
    		head = ERR_PTR(-ENOENT);
    	spin_unlock(&sysctl_lock);
    	return head;
    }
    
    static void sysctl_head_finish(struct ctl_table_header *head)
    {
    	if (!head)
    		return;
    	spin_lock(&sysctl_lock);
    	unuse_table(head);
    	spin_unlock(&sysctl_lock);
    }
    
    static struct ctl_table_set *
    lookup_header_set(struct ctl_table_root *root)
    {
    	struct ctl_table_set *set = &root->default_set;
    	if (root->lookup)
    		set = root->lookup(root);
    	return set;
    }
    
    static struct ctl_table *lookup_entry(struct ctl_table_header **phead,
    				      struct ctl_dir *dir,
    				      const char *name, int namelen)
    {
    	struct ctl_table_header *head;
    	struct ctl_table *entry;
    
    	spin_lock(&sysctl_lock);
    	entry = find_entry(&head, dir, name, namelen);
    	if (entry && use_table(head))
    		*phead = head;
    	else
    		entry = NULL;
    	spin_unlock(&sysctl_lock);
    	return entry;
    }
    
    static struct ctl_node *first_usable_entry(struct rb_node *node)
    {
    	struct ctl_node *ctl_node;
    
    	for (;node; node = rb_next(node)) {
    		ctl_node = rb_entry(node, struct ctl_node, node);
    		if (use_table(ctl_node->header))
    			return ctl_node;
    	}
    	return NULL;
    }
    
    static void first_entry(struct ctl_dir *dir,
    	struct ctl_table_header **phead, struct ctl_table **pentry)
    {
    	struct ctl_table_header *head = NULL;
    	struct ctl_table *entry = NULL;
    	struct ctl_node *ctl_node;
    
    	spin_lock(&sysctl_lock);
    	ctl_node = first_usable_entry(rb_first(&dir->root));
    	spin_unlock(&sysctl_lock);
    	if (ctl_node) {
    		head = ctl_node->header;
    		entry = &head->ctl_table[ctl_node - head->node];
    	}
    	*phead = head;
    	*pentry = entry;
    }
    
    static void next_entry(struct ctl_table_header **phead, struct ctl_table **pentry)
    {
    	struct ctl_table_header *head = *phead;
    	struct ctl_table *entry = *pentry;
    	struct ctl_node *ctl_node = &head->node[entry - head->ctl_table];
    
    	spin_lock(&sysctl_lock);
    	unuse_table(head);
    
    	ctl_node = first_usable_entry(rb_next(&ctl_node->node));
    	spin_unlock(&sysctl_lock);
    	head = NULL;
    	if (ctl_node) {
    		head = ctl_node->header;
    		entry = &head->ctl_table[ctl_node - head->node];
    	}
    	*phead = head;
    	*pentry = entry;
    }
    
    /*
     * sysctl_perm does NOT grant the superuser all rights automatically, because
     * some sysctl variables are readonly even to root.
     */
    
    static int test_perm(int mode, int op)
    {
    	if (uid_eq(current_euid(), GLOBAL_ROOT_UID))
    		mode >>= 6;
    	else if (in_egroup_p(GLOBAL_ROOT_GID))
    		mode >>= 3;
    	if ((op & ~mode & (MAY_READ|MAY_WRITE|MAY_EXEC)) == 0)
    		return 0;
    	return -EACCES;
    }
    
    static int sysctl_perm(struct ctl_table_header *head, struct ctl_table *table, int op)
    {
    	struct ctl_table_root *root = head->root;
    	int mode;
    
    	if (root->permissions)
    		mode = root->permissions(head, table);
    	else
    		mode = table->mode;
    
    	return test_perm(mode, op);
    }
    
    static struct inode *proc_sys_make_inode(struct super_block *sb,
    		struct ctl_table_header *head, struct ctl_table *table)
    {
    	struct ctl_table_root *root = head->root;
    	struct inode *inode;
    	struct proc_inode *ei;
    
    	inode = new_inode(sb);
    	if (!inode)
    		return ERR_PTR(-ENOMEM);
    
    	inode->i_ino = get_next_ino();
    
    	ei = PROC_I(inode);
    
    	spin_lock(&sysctl_lock);
    	if (unlikely(head->unregistering)) {
    		spin_unlock(&sysctl_lock);
    		iput(inode);
    		return ERR_PTR(-ENOENT);
    	}
    	ei->sysctl = head;
    	ei->sysctl_entry = table;
    	hlist_add_head_rcu(&ei->sysctl_inodes, &head->inodes);
    	head->count++;
    	spin_unlock(&sysctl_lock);
    
    	inode->i_mtime = inode->i_atime = inode->i_ctime = current_time(inode);
    	inode->i_mode = table->mode;
    	if (!S_ISDIR(table->mode)) {
    		inode->i_mode |= S_IFREG;
    		inode->i_op = &proc_sys_inode_operations;
    		inode->i_fop = &proc_sys_file_operations;
    	} else {
    		inode->i_mode |= S_IFDIR;
    		inode->i_op = &proc_sys_dir_operations;
    		inode->i_fop = &proc_sys_dir_file_operations;
    		if (is_empty_dir(head))
    			make_empty_dir_inode(inode);
    	}
    
    	if (root->set_ownership)
    		root->set_ownership(head, table, &inode->i_uid, &inode->i_gid);
    
    	return inode;
    }
    
    void proc_sys_evict_inode(struct inode *inode, struct ctl_table_header *head)
    {
    	spin_lock(&sysctl_lock);
    	hlist_del_init_rcu(&PROC_I(inode)->sysctl_inodes);
    	if (!--head->count)
    		kfree_rcu(head, rcu);
    	spin_unlock(&sysctl_lock);
    }
    
    static struct ctl_table_header *grab_header(struct inode *inode)
    {
    	struct ctl_table_header *head = PROC_I(inode)->sysctl;
    	if (!head)
    		head = &sysctl_table_root.default_set.dir.header;
    	return sysctl_head_grab(head);
    }
    
    static struct dentry *proc_sys_lookup(struct inode *dir, struct dentry *dentry,
    					unsigned int flags)
    {
    	struct ctl_table_header *head = grab_header(dir);
    	struct ctl_table_header *h = NULL;
    	const struct qstr *name = &dentry->d_name;
    	struct ctl_table *p;
    	struct inode *inode;
    	struct dentry *err = ERR_PTR(-ENOENT);
    	struct ctl_dir *ctl_dir;
    	int ret;
    
    	if (IS_ERR(head))
    		return ERR_CAST(head);
    
    	ctl_dir = container_of(head, struct ctl_dir, header);
    
    	p = lookup_entry(&h, ctl_dir, name->name, name->len);
    	if (!p)
    		goto out;
    
    	if (S_ISLNK(p->mode)) {
    		ret = sysctl_follow_link(&h, &p);
    		err = ERR_PTR(ret);
    		if (ret)
    			goto out;
    	}
    
    	inode = proc_sys_make_inode(dir->i_sb, h ? h : head, p);
    	if (IS_ERR(inode)) {
    		err = ERR_CAST(inode);
    		goto out;
    	}
    
    	d_set_d_op(dentry, &proc_sys_dentry_operations);
    	err = d_splice_alias(inode, dentry);
    
    out:
    	if (h)
    		sysctl_head_finish(h);
    	sysctl_head_finish(head);
    	return err;
    }
    
    static ssize_t proc_sys_call_handler(struct file *filp, void __user *buf,
    		size_t count, loff_t *ppos, int write)
    {
    	struct inode *inode = file_inode(filp);
    	struct ctl_table_header *head = grab_header(inode);
    	struct ctl_table *table = PROC_I(inode)->sysctl_entry;
    	ssize_t error;
    	size_t res;
    
    	if (IS_ERR(head))
    		return PTR_ERR(head);
    
    	/*
    	 * At this point we know that the sysctl was not unregistered
    	 * and won't be until we finish.
    	 */
    	error = -EPERM;
    	if (sysctl_perm(head, table, write ? MAY_WRITE : MAY_READ))
    		goto out;
    
    	/* if that can happen at all, it should be -EINVAL, not -EISDIR */
    	error = -EINVAL;
    	if (!table->proc_handler)
    		goto out;
    
    	/* careful: calling conventions are nasty here */
    	res = count;
    	error = table->proc_handler(table, write, buf, &res, ppos);
    	if (!error)
    		error = res;
    out:
    	sysctl_head_finish(head);
    
    	return error;
    }
    
    static ssize_t proc_sys_read(struct file *filp, char __user *buf,
    				size_t count, loff_t *ppos)
    {
    	return proc_sys_call_handler(filp, (void __user *)buf, count, ppos, 0);
    }
    
    static ssize_t proc_sys_write(struct file *filp, const char __user *buf,
    				size_t count, loff_t *ppos)
    {
    	return proc_sys_call_handler(filp, (void __user *)buf, count, ppos, 1);
    }
    
    static int proc_sys_open(struct inode *inode, struct file *filp)
    {
    	struct ctl_table_header *head = grab_header(inode);
    	struct ctl_table *table = PROC_I(inode)->sysctl_entry;
    
    	/* sysctl was unregistered */
    	if (IS_ERR(head))
    		return PTR_ERR(head);
    
    	if (table->poll)
    		filp->private_data = proc_sys_poll_event(table->poll);
    
    	sysctl_head_finish(head);
    
    	return 0;
    }
    
    static __poll_t proc_sys_poll(struct file *filp, poll_table *wait)
    {
    	struct inode *inode = file_inode(filp);
    	struct ctl_table_header *head = grab_header(inode);
    	struct ctl_table *table = PROC_I(inode)->sysctl_entry;
    	__poll_t ret = DEFAULT_POLLMASK;
    	unsigned long event;
    
    	/* sysctl was unregistered */
    	if (IS_ERR(head))
    		return EPOLLERR | EPOLLHUP;
    
    	if (!table->proc_handler)
    		goto out;
    
    	if (!table->poll)
    		goto out;
    
    	event = (unsigned long)filp->private_data;
    	poll_wait(filp, &table->poll->wait, wait);
    
    	if (event != atomic_read(&table->poll->event)) {
    		filp->private_data = proc_sys_poll_event(table->poll);
    		ret = EPOLLIN | EPOLLRDNORM | EPOLLERR | EPOLLPRI;
    	}
    
    out:
    	sysctl_head_finish(head);
    
    	return ret;
    }
    
    static bool proc_sys_fill_cache(struct file *file,
    				struct dir_context *ctx,
    				struct ctl_table_header *head,
    				struct ctl_table *table)
    {
    	struct dentry *child, *dir = file->f_path.dentry;
    	struct inode *inode;
    	struct qstr qname;
    	ino_t ino = 0;
    	unsigned type = DT_UNKNOWN;
    
    	qname.name = table->procname;
    	qname.len  = strlen(table->procname);
    	qname.hash = full_name_hash(dir, qname.name, qname.len);
    
    	child = d_lookup(dir, &qname);
    	if (!child) {
    		DECLARE_WAIT_QUEUE_HEAD_ONSTACK(wq);
    		child = d_alloc_parallel(dir, &qname, &wq);
    		if (IS_ERR(child))
    			return false;
    		if (d_in_lookup(child)) {
    			struct dentry *res;
    			inode = proc_sys_make_inode(dir->d_sb, head, table);
    			if (IS_ERR(inode)) {
    				d_lookup_done(child);
    				dput(child);
    				return false;
    			}
    			d_set_d_op(child, &proc_sys_dentry_operations);
    			res = d_splice_alias(inode, child);
    			d_lookup_done(child);
    			if (unlikely(res)) {
    				if (IS_ERR(res)) {
    					dput(child);
    					return false;
    				}
    				dput(child);
    				child = res;
    			}
    		}
    	}
    	inode = d_inode(child);
    	ino  = inode->i_ino;
    	type = inode->i_mode >> 12;
    	dput(child);
    	return dir_emit(ctx, qname.name, qname.len, ino, type);
    }
    
    static bool proc_sys_link_fill_cache(struct file *file,
    				    struct dir_context *ctx,
    				    struct ctl_table_header *head,
    				    struct ctl_table *table)
    {
    	bool ret = true;
    
    	head = sysctl_head_grab(head);
    	if (IS_ERR(head))
    		return false;
    
    	/* It is not an error if we can not follow the link ignore it */
    	if (sysctl_follow_link(&head, &table))
    		goto out;
    
    	ret = proc_sys_fill_cache(file, ctx, head, table);
    out:
    	sysctl_head_finish(head);
    	return ret;
    }
    
    static int scan(struct ctl_table_header *head, struct ctl_table *table,
    		unsigned long *pos, struct file *file,
    		struct dir_context *ctx)
    {
    	bool res;
    
    	if ((*pos)++ < ctx->pos)
    		return true;
    
    	if (unlikely(S_ISLNK(table->mode)))
    		res = proc_sys_link_fill_cache(file, ctx, head, table);
    	else
    		res = proc_sys_fill_cache(file, ctx, head, table);
    
    	if (res)
    		ctx->pos = *pos;
    
    	return res;
    }
    
    static int proc_sys_readdir(struct file *file, struct dir_context *ctx)
    {
    	struct ctl_table_header *head = grab_header(file_inode(file));
    	struct ctl_table_header *h = NULL;
    	struct ctl_table *entry;
    	struct ctl_dir *ctl_dir;
    	unsigned long pos;
    
    	if (IS_ERR(head))
    		return PTR_ERR(head);
    
    	ctl_dir = container_of(head, struct ctl_dir, header);
    
    	if (!dir_emit_dots(file, ctx))
    		goto out;
    
    	pos = 2;
    
    	for (first_entry(ctl_dir, &h, &entry); h; next_entry(&h, &entry)) {
    		if (!scan(h, entry, &pos, file, ctx)) {
    			sysctl_head_finish(h);
    			break;
    		}
    	}
    out:
    	sysctl_head_finish(head);
    	return 0;
    }
    
    static int proc_sys_permission(struct inode *inode, int mask)
    {
    	/*
    	 * sysctl entries that are not writeable,
    	 * are _NOT_ writeable, capabilities or not.
    	 */
    	struct ctl_table_header *head;
    	struct ctl_table *table;
    	int error;
    
    	/* Executable files are not allowed under /proc/sys/ */
    	if ((mask & MAY_EXEC) && S_ISREG(inode->i_mode))
    		return -EACCES;
    
    	head = grab_header(inode);
    	if (IS_ERR(head))
    		return PTR_ERR(head);
    
    	table = PROC_I(inode)->sysctl_entry;
    	if (!table) /* global root - r-xr-xr-x */
    		error = mask & MAY_WRITE ? -EACCES : 0;
    	else /* Use the permissions on the sysctl table entry */
    		error = sysctl_perm(head, table, mask & ~MAY_NOT_BLOCK);
    
    	sysctl_head_finish(head);
    	return error;
    }
    
    static int proc_sys_setattr(struct dentry *dentry, struct iattr *attr)
    {
    	struct inode *inode = d_inode(dentry);
    	int error;
    
    	if (attr->ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID))
    		return -EPERM;
    
    	error = setattr_prepare(dentry, attr);
    	if (error)
    		return error;
    
    	setattr_copy(inode, attr);
    	mark_inode_dirty(inode);
    	return 0;
    }
    
    static int proc_sys_getattr(const struct path *path, struct kstat *stat,
    			    u32 request_mask, unsigned int query_flags)
    {
    	struct inode *inode = d_inode(path->dentry);
    	struct ctl_table_header *head = grab_header(inode);
    	struct ctl_table *table = PROC_I(inode)->sysctl_entry;
    
    	if (IS_ERR(head))
    		return PTR_ERR(head);
    
    	generic_fillattr(inode, stat);
    	if (table)
    		stat->mode = (stat->mode & S_IFMT) | table->mode;
    
    	sysctl_head_finish(head);
    	return 0;
    }
    
    static const struct file_operations proc_sys_file_operations = {
    	.open		= proc_sys_open,
    	.poll		= proc_sys_poll,
    	.read		= proc_sys_read,
    	.write		= proc_sys_write,
    	.llseek		= default_llseek,
    };
    
    static const struct file_operations proc_sys_dir_file_operations = {
    	.read		= generic_read_dir,
    	.iterate_shared	= proc_sys_readdir,
    	.llseek		= generic_file_llseek,
    };
    
    static const struct inode_operations proc_sys_inode_operations = {
    	.permission	= proc_sys_permission,
    	.setattr	= proc_sys_setattr,
    	.getattr	= proc_sys_getattr,
    };
    
    static const struct inode_operations proc_sys_dir_operations = {
    	.lookup		= proc_sys_lookup,
    	.permission	= proc_sys_permission,
    	.setattr	= proc_sys_setattr,
    	.getattr	= proc_sys_getattr,
    };
    
    static int proc_sys_revalidate(struct dentry *dentry, unsigned int flags)
    {
    	if (flags & LOOKUP_RCU)
    		return -ECHILD;
    	return !PROC_I(d_inode(dentry))->sysctl->unregistering;
    }
    
    static int proc_sys_delete(const struct dentry *dentry)
    {
    	return !!PROC_I(d_inode(dentry))->sysctl->unregistering;
    }
    
    static int sysctl_is_seen(struct ctl_table_header *p)
    {
    	struct ctl_table_set *set = p->set;
    	int res;
    	spin_lock(&sysctl_lock);
    	if (p->unregistering)
    		res = 0;
    	else if (!set->is_seen)
    		res = 1;
    	else
    		res = set->is_seen(set);
    	spin_unlock(&sysctl_lock);
    	return res;
    }
    
    static int proc_sys_compare(const struct dentry *dentry,
    		unsigned int len, const char *str, const struct qstr *name)
    {
    	struct ctl_table_header *head;
    	struct inode *inode;
    
    	/* Although proc doesn't have negative dentries, rcu-walk means
    	 * that inode here can be NULL */
    	/* AV: can it, indeed? */
    	inode = d_inode_rcu(dentry);
    	if (!inode)
    		return 1;
    	if (name->len != len)
    		return 1;
    	if (memcmp(name->name, str, len))
    		return 1;
    	head = rcu_dereference(PROC_I(inode)->sysctl);
    	return !head || !sysctl_is_seen(head);
    }
    
    static const struct dentry_operations proc_sys_dentry_operations = {
    	.d_revalidate	= proc_sys_revalidate,
    	.d_delete	= proc_sys_delete,
    	.d_compare	= proc_sys_compare,
    };
    
    static struct ctl_dir *find_subdir(struct ctl_dir *dir,
    				   const char *name, int namelen)
    {
    	struct ctl_table_header *head;
    	struct ctl_table *entry;
    
    	entry = find_entry(&head, dir, name, namelen);
    	if (!entry)
    		return ERR_PTR(-ENOENT);
    	if (!S_ISDIR(entry->mode))
    		return ERR_PTR(-ENOTDIR);
    	return container_of(head, struct ctl_dir, header);
    }
    
    static struct ctl_dir *new_dir(struct ctl_table_set *set,
    			       const char *name, int namelen)
    {
    	struct ctl_table *table;
    	struct ctl_dir *new;
    	struct ctl_node *node;
    	char *new_name;
    
    	new = kzalloc(sizeof(*new) + sizeof(struct ctl_node) +
    		      sizeof(struct ctl_table)*2 +  namelen + 1,
    		      GFP_KERNEL);
    	if (!new)
    		return NULL;
    
    	node = (struct ctl_node *)(new + 1);
    	table = (struct ctl_table *)(node + 1);
    	new_name = (char *)(table + 2);
    	memcpy(new_name, name, namelen);
    	new_name[namelen] = '\0';
    	table[0].procname = new_name;
    	table[0].mode = S_IFDIR|S_IRUGO|S_IXUGO;
    	init_header(&new->header, set->dir.header.root, set, node, table);
    
    	return new;
    }
    
    /**
     * get_subdir - find or create a subdir with the specified name.
     * @dir:  Directory to create the subdirectory in
     * @name: The name of the subdirectory to find or create
     * @namelen: The length of name
     *
     * Takes a directory with an elevated reference count so we know that
     * if we drop the lock the directory will not go away.  Upon success
     * the reference is moved from @dir to the returned subdirectory.
     * Upon error an error code is returned and the reference on @dir is
     * simply dropped.
     */
    static struct ctl_dir *get_subdir(struct ctl_dir *dir,
    				  const char *name, int namelen)
    {
    	struct ctl_table_set *set = dir->header.set;
    	struct ctl_dir *subdir, *new = NULL;
    	int err;
    
    	spin_lock(&sysctl_lock);
    	subdir = find_subdir(dir, name, namelen);
    	if (!IS_ERR(subdir))
    		goto found;
    	if (PTR_ERR(subdir) != -ENOENT)
    		goto failed;
    
    	spin_unlock(&sysctl_lock);
    	new = new_dir(set, name, namelen);
    	spin_lock(&sysctl_lock);
    	subdir = ERR_PTR(-ENOMEM);
    	if (!new)
    		goto failed;
    
    	/* Was the subdir added while we dropped the lock? */
    	subdir = find_subdir(dir, name, namelen);
    	if (!IS_ERR(subdir))
    		goto found;
    	if (PTR_ERR(subdir) != -ENOENT)
    		goto failed;
    
    	/* Nope.  Use the our freshly made directory entry. */
    	err = insert_header(dir, &new->header);
    	subdir = ERR_PTR(err);
    	if (err)
    		goto failed;
    	subdir = new;
    found:
    	subdir->header.nreg++;
    failed:
    	if (IS_ERR(subdir)) {
    		pr_err("sysctl could not get directory: ");
    		sysctl_print_dir(dir);
    		pr_cont("/%*.*s %ld\n",
    			namelen, namelen, name, PTR_ERR(subdir));
    	}
    	drop_sysctl_table(&dir->header);
    	if (new)
    		drop_sysctl_table(&new->header);
    	spin_unlock(&sysctl_lock);
    	return subdir;
    }
    
    static struct ctl_dir *xlate_dir(struct ctl_table_set *set, struct ctl_dir *dir)
    {
    	struct ctl_dir *parent;
    	const char *procname;
    	if (!dir->header.parent)
    		return &set->dir;
    	parent = xlate_dir(set, dir->header.parent);
    	if (IS_ERR(parent))
    		return parent;
    	procname = dir->header.ctl_table[0].procname;
    	return find_subdir(parent, procname, strlen(procname));
    }
    
    static int sysctl_follow_link(struct ctl_table_header **phead,
    	struct ctl_table **pentry)
    {
    	struct ctl_table_header *head;
    	struct ctl_table_root *root;
    	struct ctl_table_set *set;
    	struct ctl_table *entry;
    	struct ctl_dir *dir;
    	int ret;
    
    	ret = 0;
    	spin_lock(&sysctl_lock);
    	root = (*pentry)->data;
    	set = lookup_header_set(root);
    	dir = xlate_dir(set, (*phead)->parent);
    	if (IS_ERR(dir))
    		ret = PTR_ERR(dir);
    	else {
    		const char *procname = (*pentry)->procname;
    		head = NULL;
    		entry = find_entry(&head, dir, procname, strlen(procname));
    		ret = -ENOENT;
    		if (entry && use_table(head)) {
    			unuse_table(*phead);
    			*phead = head;
    			*pentry = entry;
    			ret = 0;
    		}
    	}
    
    	spin_unlock(&sysctl_lock);
    	return ret;
    }
    
    static int sysctl_err(const char *path, struct ctl_table *table, char *fmt, ...)
    {
    	struct va_format vaf;
    	va_list args;
    
    	va_start(args, fmt);
    	vaf.fmt = fmt;
    	vaf.va = &args;
    
    	pr_err("sysctl table check failed: %s/%s %pV\n",
    	       path, table->procname, &vaf);
    
    	va_end(args);
    	return -EINVAL;
    }
    
    static int sysctl_check_table_array(const char *path, struct ctl_table *table)
    {
    	int err = 0;
    
    	if ((table->proc_handler == proc_douintvec) ||
    	    (table->proc_handler == proc_douintvec_minmax)) {
    		if (table->maxlen != sizeof(unsigned int))
    			err |= sysctl_err(path, table, "array not allowed");
    	}
    
    	return err;
    }
    
    static int sysctl_check_table(const char *path, struct ctl_table *table)
    {
    	int err = 0;
    	for (; table->procname; table++) {
    		if (table->child)
    			err |= sysctl_err(path, table, "Not a file");
    
    		if ((table->proc_handler == proc_dostring) ||
    		    (table->proc_handler == proc_dointvec) ||
    		    (table->proc_handler == proc_douintvec) ||
    		    (table->proc_handler == proc_douintvec_minmax) ||
    		    (table->proc_handler == proc_dointvec_minmax) ||
    		    (table->proc_handler == proc_dointvec_jiffies) ||
    		    (table->proc_handler == proc_dointvec_userhz_jiffies) ||
    		    (table->proc_handler == proc_dointvec_ms_jiffies) ||
    		    (table->proc_handler == proc_doulongvec_minmax) ||
    		    (table->proc_handler == proc_doulongvec_ms_jiffies_minmax)) {
    			if (!table->data)
    				err |= sysctl_err(path, table, "No data");
    			if (!table->maxlen)
    				err |= sysctl_err(path, table, "No maxlen");
    			else
    				err |= sysctl_check_table_array(path, table);
    		}
    		if (!table->proc_handler)
    			err |= sysctl_err(path, table, "No proc_handler");
    
    		if ((table->mode & (S_IRUGO|S_IWUGO)) != table->mode)
    			err |= sysctl_err(path, table, "bogus .mode 0%o",
    				table->mode);
    	}
    	return err;
    }
    
    static struct ctl_table_header *new_links(struct ctl_dir *dir, struct ctl_table *table,
    	struct ctl_table_root *link_root)
    {
    	struct ctl_table *link_table, *entry, *link;
    	struct ctl_table_header *links;
    	struct ctl_node *node;
    	char *link_name;
    	int nr_entries, name_bytes;
    
    	name_bytes = 0;
    	nr_entries = 0;
    	for (entry = table; entry->procname; entry++) {
    		nr_entries++;
    		name_bytes += strlen(entry->procname) + 1;
    	}
    
    	links = kzalloc(sizeof(struct ctl_table_header) +
    			sizeof(struct ctl_node)*nr_entries +
    			sizeof(struct ctl_table)*(nr_entries + 1) +
    			name_bytes,
    			GFP_KERNEL);
    
    	if (!links)
    		return NULL;
    
    	node = (struct ctl_node *)(links + 1);
    	link_table = (struct ctl_table *)(node + nr_entries);
    	link_name = (char *)&link_table[nr_entries + 1];
    
    	for (link = link_table, entry = table; entry->procname; link++, entry++) {
    		int len = strlen(entry->procname) + 1;
    		memcpy(link_name, entry->procname, len);
    		link->procname = link_name;
    		link->mode = S_IFLNK|S_IRWXUGO;
    		link->data = link_root;
    		link_name += len;
    	}
    	init_header(links, dir->header.root, dir->header.set, node, link_table);
    	links->nreg = nr_entries;
    
    	return links;
    }
    
    static bool get_links(struct ctl_dir *dir,
    	struct ctl_table *table, struct ctl_table_root *link_root)
    {
    	struct ctl_table_header *head;
    	struct ctl_table *entry, *link;
    
    	/* Are there links available for every entry in table? */
    	for (entry = table; entry->procname; entry++) {
    		const char *procname = entry->procname;
    		link = find_entry(&head, dir, procname, strlen(procname));
    		if (!link)
    			return false;
    		if (S_ISDIR(link->mode) && S_ISDIR(entry->mode))
    			continue;
    		if (S_ISLNK(link->mode) && (link->data == link_root))
    			continue;
    		return false;
    	}
    
    	/* The checks passed.  Increase the registration count on the links */
    	for (entry = table; entry->procname; entry++) {
    		const char *procname = entry->procname;
    		link = find_entry(&head, dir, procname, strlen(procname));
    		head->nreg++;
    	}
    	return true;
    }
    
    static int insert_links(struct ctl_table_header *head)
    {
    	struct ctl_table_set *root_set = &sysctl_table_root.default_set;
    	struct ctl_dir *core_parent = NULL;
    	struct ctl_table_header *links;
    	int err;
    
    	if (head->set == root_set)
    		return 0;
    
    	core_parent = xlate_dir(root_set, head->parent);
    	if (IS_ERR(core_parent))
    		return 0;
    
    	if (get_links(core_parent, head->ctl_table, head->root))
    		return 0;
    
    	core_parent->header.nreg++;
    	spin_unlock(&sysctl_lock);
    
    	links = new_links(core_parent, head->ctl_table, head->root);
    
    	spin_lock(&sysctl_lock);
    	err = -ENOMEM;
    	if (!links)
    		goto out;
    
    	err = 0;
    	if (get_links(core_parent, head->ctl_table, head->root)) {
    		kfree(links);
    		goto out;
    	}
    
    	err = insert_header(core_parent, links);
    	if (err)
    		kfree(links);
    out:
    	drop_sysctl_table(&core_parent->header);
    	return err;
    }
    
    /**
     * __register_sysctl_table - register a leaf sysctl table
     * @set: Sysctl tree to register on
     * @path: The path to the directory the sysctl table is in.
     * @table: the top-level table structure
     *
     * Register a sysctl table hierarchy. @table should be a filled in ctl_table
     * array. A completely 0 filled entry terminates the table.
     *
     * The members of the &struct ctl_table structure are used as follows:
     *
     * procname - the name of the sysctl file under /proc/sys. Set to %NULL to not
     *            enter a sysctl file
     *
     * data - a pointer to data for use by proc_handler
     *
     * maxlen - the maximum size in bytes of the data
     *
     * mode - the file permissions for the /proc/sys file
     *
     * child - must be %NULL.
     *
     * proc_handler - the text handler routine (described below)
     *
     * extra1, extra2 - extra pointers usable by the proc handler routines
     *
     * Leaf nodes in the sysctl tree will be represented by a single file
     * under /proc; non-leaf nodes will be represented by directories.
     *
     * There must be a proc_handler routine for any terminal nodes.
     * Several default handlers are available to cover common cases -
     *
     * proc_dostring(), proc_dointvec(), proc_dointvec_jiffies(),
     * proc_dointvec_userhz_jiffies(), proc_dointvec_minmax(),
     * proc_doulongvec_ms_jiffies_minmax(), proc_doulongvec_minmax()
     *
     * It is the handler's job to read the input buffer from user memory
     * and process it. The handler should return 0 on success.
     *
     * This routine returns %NULL on a failure to register, and a pointer
     * to the table header on success.
     */
    struct ctl_table_header *__register_sysctl_table(
    	struct ctl_table_set *set,
    	const char *path, struct ctl_table *table)
    {
    	struct ctl_table_root *root = set->dir.header.root;
    	struct ctl_table_header *header;
    	const char *name, *nextname;
    	struct ctl_dir *dir;
    	struct ctl_table *entry;
    	struct ctl_node *node;
    	int nr_entries = 0;
    
    	for (entry = table; entry->procname; entry++)
    		nr_entries++;
    
    	header = kzalloc(sizeof(struct ctl_table_header) +
    			 sizeof(struct ctl_node)*nr_entries, GFP_KERNEL);
    	if (!header)
    		return NULL;
    
    	node = (struct ctl_node *)(header + 1);
    	init_header(header, root, set, node, table);
    	if (sysctl_check_table(path, table))
    		goto fail;
    
    	spin_lock(&sysctl_lock);
    	dir = &set->dir;
    	/* Reference moved down the diretory tree get_subdir */
    	dir->header.nreg++;
    	spin_unlock(&sysctl_lock);
    
    	/* Find the directory for the ctl_table */
    	for (name = path; name; name = nextname) {
    		int namelen;
    		nextname = strchr(name, '/');
    		if (nextname) {
    			namelen = nextname - name;
    			nextname++;
    		} else {
    			namelen = strlen(name);
    		}
    		if (namelen == 0)
    			continue;
    
    		dir = get_subdir(dir, name, namelen);
    		if (IS_ERR(dir))
    			goto fail;
    	}
    
    	spin_lock(&sysctl_lock);
    	if (insert_header(dir, header))
    		goto fail_put_dir_locked;
    
    	drop_sysctl_table(&dir->header);
    	spin_unlock(&sysctl_lock);
    
    	return header;
    
    fail_put_dir_locked:
    	drop_sysctl_table(&dir->header);
    	spin_unlock(&sysctl_lock);
    fail:
    	kfree(header);
    	dump_stack();
    	return NULL;
    }
    
    /**
     * register_sysctl - register a sysctl table
     * @path: The path to the directory the sysctl table is in.
     * @table: the table structure
     *
     * Register a sysctl table. @table should be a filled in ctl_table
     * array. A completely 0 filled entry terminates the table.
     *
     * See __register_sysctl_table for more details.
     */
    struct ctl_table_header *register_sysctl(const char *path, struct ctl_table *table)
    {
    	return __register_sysctl_table(&sysctl_table_root.default_set,
    					path, table);
    }
    EXPORT_SYMBOL(register_sysctl);
    
    static char *append_path(const char *path, char *pos, const char *name)
    {
    	int namelen;
    	namelen = strlen(name);
    	if (((pos - path) + namelen + 2) >= PATH_MAX)
    		return NULL;
    	memcpy(pos, name, namelen);
    	pos[namelen] = '/';
    	pos[namelen + 1] = '\0';
    	pos += namelen + 1;
    	return pos;
    }
    
    static int count_subheaders(struct ctl_table *table)
    {
    	int has_files = 0;
    	int nr_subheaders = 0;
    	struct ctl_table *entry;
    
    	/* special case: no directory and empty directory */
    	if (!table || !table->procname)
    		return 1;
    
    	for (entry = table; entry->procname; entry++) {
    		if (entry->child)
    			nr_subheaders += count_subheaders(entry->child);
    		else
    			has_files = 1;
    	}
    	return nr_subheaders + has_files;
    }
    
    static int register_leaf_sysctl_tables(const char *path, char *pos,
    	struct ctl_table_header ***subheader, struct ctl_table_set *set,
    	struct ctl_table *table)
    {
    	struct ctl_table *ctl_table_arg = NULL;
    	struct ctl_table *entry, *files;
    	int nr_files = 0;
    	int nr_dirs = 0;
    	int err = -ENOMEM;
    
    	for (entry = table; entry->procname; entry++) {
    		if (entry->child)
    			nr_dirs++;
    		else
    			nr_files++;
    	}
    
    	files = table;
    	/* If there are mixed files and directories we need a new table */
    	if (nr_dirs && nr_files) {
    		struct ctl_table *new;
    		files = kcalloc(nr_files + 1, sizeof(struct ctl_table),
    				GFP_KERNEL);
    		if (!files)
    			goto out;
    
    		ctl_table_arg = files;
    		for (new = files, entry = table; entry->procname; entry++) {
    			if (entry->child)
    				continue;
    			*new = *entry;
    			new++;
    		}
    	}
    
    	/* Register everything except a directory full of subdirectories */
    	if (nr_files || !nr_dirs) {
    		struct ctl_table_header *header;
    		header = __register_sysctl_table(set, path, files);
    		if (!header) {
    			kfree(ctl_table_arg);
    			goto out;
    		}
    
    		/* Remember if we need to free the file table */
    		header->ctl_table_arg = ctl_table_arg;
    		**subheader = header;
    		(*subheader)++;
    	}
    
    	/* Recurse into the subdirectories. */
    	for (entry = table; entry->procname; entry++) {
    		char *child_pos;
    
    		if (!entry->child)
    			continue;
    
    		err = -ENAMETOOLONG;
    		child_pos = append_path(path, pos, entry->procname);
    		if (!child_pos)
    			goto out;
    
    		err = register_leaf_sysctl_tables(path, child_pos, subheader,
    						  set, entry->child);
    		pos[0] = '\0';
    		if (err)
    			goto out;
    	}
    	err = 0;
    out:
    	/* On failure our caller will unregister all registered subheaders */
    	return err;
    }
    
    /**
     * __register_sysctl_paths - register a sysctl table hierarchy
     * @set: Sysctl tree to register on
     * @path: The path to the directory the sysctl table is in.
     * @table: the top-level table structure
     *
     * Register a sysctl table hierarchy. @table should be a filled in ctl_table
     * array. A completely 0 filled entry terminates the table.
     *
     * See __register_sysctl_table for more details.
     */
    struct ctl_table_header *__register_sysctl_paths(
    	struct ctl_table_set *set,
    	const struct ctl_path *path, struct ctl_table *table)
    {
    	struct ctl_table *ctl_table_arg = table;
    	int nr_subheaders = count_subheaders(table);
    	struct ctl_table_header *header = NULL, **subheaders, **subheader;
    	const struct ctl_path *component;
    	char *new_path, *pos;
    
    	pos = new_path = kmalloc(PATH_MAX, GFP_KERNEL);
    	if (!new_path)
    		return NULL;
    
    	pos[0] = '\0';
    	for (component = path; component->procname; component++) {
    		pos = append_path(new_path, pos, component->procname);
    		if (!pos)
    			goto out;
    	}
    	while (table->procname && table->child && !table[1].procname) {
    		pos = append_path(new_path, pos, table->procname);
    		if (!pos)
    			goto out;
    		table = table->child;
    	}
    	if (nr_subheaders == 1) {
    		header = __register_sysctl_table(set, new_path, table);
    		if (header)
    			header->ctl_table_arg = ctl_table_arg;
    	} else {
    		header = kzalloc(sizeof(*header) +
    				 sizeof(*subheaders)*nr_subheaders, GFP_KERNEL);
    		if (!header)
    			goto out;
    
    		subheaders = (struct ctl_table_header **) (header + 1);
    		subheader = subheaders;
    		header->ctl_table_arg = ctl_table_arg;
    
    		if (register_leaf_sysctl_tables(new_path, pos, &subheader,
    						set, table))
    			goto err_register_leaves;
    	}
    
    out:
    	kfree(new_path);
    	return header;
    
    err_register_leaves:
    	while (subheader > subheaders) {
    		struct ctl_table_header *subh = *(--subheader);
    		struct ctl_table *table = subh->ctl_table_arg;
    		unregister_sysctl_table(subh);
    		kfree(table);
    	}
    	kfree(header);
    	header = NULL;
    	goto out;
    }
    
    /**
     * register_sysctl_table_path - register a sysctl table hierarchy
     * @path: The path to the directory the sysctl table is in.
     * @table: the top-level table structure
     *
     * Register a sysctl table hierarchy. @table should be a filled in ctl_table
     * array. A completely 0 filled entry terminates the table.
     *
     * See __register_sysctl_paths for more details.
     */
    struct ctl_table_header *register_sysctl_paths(const struct ctl_path *path,
    						struct ctl_table *table)
    {
    	return __register_sysctl_paths(&sysctl_table_root.default_set,
    					path, table);
    }
    EXPORT_SYMBOL(register_sysctl_paths);
    
    /**
     * register_sysctl_table - register a sysctl table hierarchy
     * @table: the top-level table structure
     *
     * Register a sysctl table hierarchy. @table should be a filled in ctl_table
     * array. A completely 0 filled entry terminates the table.
     *
     * See register_sysctl_paths for more details.
     */
    struct ctl_table_header *register_sysctl_table(struct ctl_table *table)
    {
    	static const struct ctl_path null_path[] = { {} };
    
    	return register_sysctl_paths(null_path, table);
    }
    EXPORT_SYMBOL(register_sysctl_table);
    
    static void put_links(struct ctl_table_header *header)
    {
    	struct ctl_table_set *root_set = &sysctl_table_root.default_set;
    	struct ctl_table_root *root = header->root;
    	struct ctl_dir *parent = header->parent;
    	struct ctl_dir *core_parent;
    	struct ctl_table *entry;
    
    	if (header->set == root_set)
    		return;
    
    	core_parent = xlate_dir(root_set, parent);
    	if (IS_ERR(core_parent))
    		return;
    
    	for (entry = header->ctl_table; entry->procname; entry++) {
    		struct ctl_table_header *link_head;
    		struct ctl_table *link;
    		const char *name = entry->procname;
    
    		link = find_entry(&link_head, core_parent, name, strlen(name));
    		if (link &&
    		    ((S_ISDIR(link->mode) && S_ISDIR(entry->mode)) ||
    		     (S_ISLNK(link->mode) && (link->data == root)))) {
    			drop_sysctl_table(link_head);
    		}
    		else {
    			pr_err("sysctl link missing during unregister: ");
    			sysctl_print_dir(parent);
    			pr_cont("/%s\n", name);
    		}
    	}
    }
    
    static void drop_sysctl_table(struct ctl_table_header *header)
    {
    	struct ctl_dir *parent = header->parent;
    
    	if (--header->nreg)
    		return;
    
    	put_links(header);
    	start_unregistering(header);
    	if (!--header->count)
    		kfree_rcu(header, rcu);
    
    	if (parent)
    		drop_sysctl_table(&parent->header);
    }
    
    /**
     * unregister_sysctl_table - unregister a sysctl table hierarchy
     * @header: the header returned from register_sysctl_table
     *
     * Unregisters the sysctl table and all children. proc entries may not
     * actually be removed until they are no longer used by anyone.
     */
    void unregister_sysctl_table(struct ctl_table_header * header)
    {
    	int nr_subheaders;
    	might_sleep();
    
    	if (header == NULL)
    		return;
    
    	nr_subheaders = count_subheaders(header->ctl_table_arg);
    	if (unlikely(nr_subheaders > 1)) {
    		struct ctl_table_header **subheaders;
    		int i;
    
    		subheaders = (struct ctl_table_header **)(header + 1);
    		for (i = nr_subheaders -1; i >= 0; i--) {
    			struct ctl_table_header *subh = subheaders[i];
    			struct ctl_table *table = subh->ctl_table_arg;
    			unregister_sysctl_table(subh);
    			kfree(table);
    		}
    		kfree(header);
    		return;
    	}
    
    	spin_lock(&sysctl_lock);
    	drop_sysctl_table(header);
    	spin_unlock(&sysctl_lock);
    }
    EXPORT_SYMBOL(unregister_sysctl_table);
    
    void setup_sysctl_set(struct ctl_table_set *set,
    	struct ctl_table_root *root,
    	int (*is_seen)(struct ctl_table_set *))
    {
    	memset(set, 0, sizeof(*set));
    	set->is_seen = is_seen;
    	init_header(&set->dir.header, root, set, NULL, root_table);
    }
    
    void retire_sysctl_set(struct ctl_table_set *set)
    {
    	WARN_ON(!RB_EMPTY_ROOT(&set->dir.root));
    }
    
    int __init proc_sys_init(void)
    {
    	struct proc_dir_entry *proc_sys_root;
    
    	proc_sys_root = proc_mkdir("sys", NULL);
    	proc_sys_root->proc_iops = &proc_sys_dir_operations;
    	proc_sys_root->proc_fops = &proc_sys_dir_file_operations;
    	proc_sys_root->nlink = 0;
    
    	return sysctl_init();
    }