fs/proc/proc_sysctl.c - kernel/msm-5.4 - Gitiles

 /*
  * /proc/sys support
  */

 #include <linux/sysctl.h>
 #include <linux/proc_fs.h>
 #include <linux/security.h>
 #include "internal.h"

 static 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 void proc_sys_refresh_inode(struct inode *inode, struct ctl_table *table)
 {
 	/* Refresh the cached information bits in the inode */
 	if (table) {
 		inode->i_uid = 0;
 		inode->i_gid = 0;
 		inode->i_mode = table->mode;
 		if (table->proc_handler) {
 			inode->i_mode |= S_IFREG;
 			inode->i_nlink = 1;
 		} else {
 			inode->i_mode |= S_IFDIR;
 			inode->i_nlink = 0;	/* It is too hard to figure out */
 		}
 	}
 }

 static struct inode *proc_sys_make_inode(struct inode *dir, struct ctl_table *table)
 {
 	struct inode *inode;
 	struct proc_inode *dir_ei, *ei;
 	int depth;

 	inode = new_inode(dir->i_sb);
 	if (!inode)
 		goto out;

 	/* A directory is always one deeper than it's parent */
 	dir_ei = PROC_I(dir);
 	depth = dir_ei->fd + 1;

 	ei = PROC_I(inode);
 	ei->fd = depth;
 	inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
 	inode->i_op = &proc_sys_inode_operations;
 	inode->i_fop = &proc_sys_file_operations;
 	inode->i_flags |= S_PRIVATE; /* tell selinux to ignore this inode */
 	proc_sys_refresh_inode(inode, table);
 out:
 	return inode;
 }

 static struct dentry *proc_sys_ancestor(struct dentry *dentry, int depth)
 {
 	for (;;) {
 		struct proc_inode *ei;

 		ei = PROC_I(dentry->d_inode);
 		if (ei->fd == depth)
 			break; /* found */

 		dentry = dentry->d_parent;
 	}
 	return dentry;
 }

 static struct ctl_table *proc_sys_lookup_table_one(struct ctl_table *table,
 							struct qstr *name)
 {
 	int len;
 	for ( ; table->ctl_name || table->procname; table++) {

 		if (!table->procname)
 			continue;

 		len = strlen(table->procname);
 		if (len != name->len)
 			continue;

 		if (memcmp(table->procname, name->name, len) != 0)
 			continue;

 		/* I have a match */
 		return table;
 	}
 	return NULL;
 }

 static struct ctl_table *proc_sys_lookup_table(struct dentry *dentry,
 						struct ctl_table *table)
 {
 	struct dentry *ancestor;
 	struct proc_inode *ei;
 	int depth, i;

 	ei = PROC_I(dentry->d_inode);
 	depth = ei->fd;

 	if (depth == 0)
 		return table;

 	for (i = 1; table && (i <= depth); i++) {
 		ancestor = proc_sys_ancestor(dentry, i);
 		table = proc_sys_lookup_table_one(table, &ancestor->d_name);
 		if (table)
 			table = table->child;
 	}
 	return table;

 }
 static struct ctl_table *proc_sys_lookup_entry(struct dentry *dparent,
 						struct qstr *name,
 						struct ctl_table *table)
 {
 	table = proc_sys_lookup_table(dparent, table);
 	if (table)
 		table = proc_sys_lookup_table_one(table, name);
 	return table;
 }

 static struct ctl_table *do_proc_sys_lookup(struct dentry *parent,
 						struct qstr *name,
 						struct ctl_table_header **ptr)
 {
 	struct ctl_table_header *head;
 	struct ctl_table *table = NULL;

 	for (head = sysctl_head_next(NULL); head;
 			head = sysctl_head_next(head)) {
 		table = proc_sys_lookup_entry(parent, name, head->ctl_table);
 		if (table)
 			break;
 	}
 	*ptr = head;
 	return table;
 }

 static struct dentry *proc_sys_lookup(struct inode *dir, struct dentry *dentry,
 					struct nameidata *nd)
 {
 	struct ctl_table_header *head;
 	struct inode *inode;
 	struct dentry *err;
 	struct ctl_table *table;

 	err = ERR_PTR(-ENOENT);
 	table = do_proc_sys_lookup(dentry->d_parent, &dentry->d_name, &head);
 	if (!table)
 		goto out;

 	err = ERR_PTR(-ENOMEM);
 	inode = proc_sys_make_inode(dir, table);
 	if (!inode)
 		goto out;

 	err = NULL;
 	dentry->d_op = &proc_sys_dentry_operations;
 	d_add(dentry, inode);

 out:
 	sysctl_head_finish(head);
 	return err;
 }

 static ssize_t proc_sys_read(struct file *filp, char __user *buf,
 				size_t count, loff_t *ppos)
 {
 	struct dentry *dentry = filp->f_dentry;
 	struct ctl_table_header *head;
 	struct ctl_table *table;
 	ssize_t error;
 	size_t res;

 	table = do_proc_sys_lookup(dentry->d_parent, &dentry->d_name, &head);
 	/* Has the sysctl entry disappeared on us? */
 	error = -ENOENT;
 	if (!table)
 		goto out;

 	/* Has the sysctl entry been replaced by a directory? */
 	error = -EISDIR;
 	if (!table->proc_handler)
 		goto out;

 	/*
 	 * At this point we know that the sysctl was not unregistered
 	 * and won't be until we finish.
 	 */
 	error = -EPERM;
 	if (sysctl_perm(table, MAY_READ))
 		goto out;

 	/* careful: calling conventions are nasty here */
 	res = count;
 	error = table->proc_handler(table, 0, filp, buf, &res, ppos);
 	if (!error)
 		error = res;
 out:
 	sysctl_head_finish(head);

 	return error;
 }

 static ssize_t proc_sys_write(struct file *filp, const char __user *buf,
 				size_t count, loff_t *ppos)
 {
 	struct dentry *dentry = filp->f_dentry;
 	struct ctl_table_header *head;
 	struct ctl_table *table;
 	ssize_t error;
 	size_t res;

 	table = do_proc_sys_lookup(dentry->d_parent, &dentry->d_name, &head);
 	/* Has the sysctl entry disappeared on us? */
 	error = -ENOENT;
 	if (!table)
 		goto out;

 	/* Has the sysctl entry been replaced by a directory? */
 	error = -EISDIR;
 	if (!table->proc_handler)
 		goto out;

 	/*
 	 * At this point we know that the sysctl was not unregistered
 	 * and won't be until we finish.
 	 */
 	error = -EPERM;
 	if (sysctl_perm(table, MAY_WRITE))
 		goto out;

 	/* careful: calling conventions are nasty here */
 	res = count;
 	error = table->proc_handler(table, 1, filp, (char __user *)buf,
 				    &res, ppos);
 	if (!error)
 		error = res;
 out:
 	sysctl_head_finish(head);

 	return error;
 }


 static int proc_sys_fill_cache(struct file *filp, void *dirent,
 				filldir_t filldir, struct ctl_table *table)
 {
 	struct ctl_table_header *head;
 	struct ctl_table *child_table = NULL;
 	struct dentry *child, *dir = filp->f_path.dentry;
 	struct inode *inode;
 	struct qstr qname;
 	ino_t ino = 0;
 	unsigned type = DT_UNKNOWN;
 	int ret;

 	qname.name = table->procname;
 	qname.len  = strlen(table->procname);
 	qname.hash = full_name_hash(qname.name, qname.len);

 	/* Suppress duplicates.
 	 * Only fill a directory entry if it is the value that
 	 * an ordinary lookup of that name returns.  Hide all
 	 * others.
 	 *
 	 * If we ever cache this translation in the dcache
 	 * I should do a dcache lookup first.  But for now
 	 * it is just simpler not to.
 	 */
 	ret = 0;
 	child_table = do_proc_sys_lookup(dir, &qname, &head);
 	sysctl_head_finish(head);
 	if (child_table != table)
 		return 0;

 	child = d_lookup(dir, &qname);
 	if (!child) {
 		struct dentry *new;
 		new = d_alloc(dir, &qname);
 		if (new) {
 			inode = proc_sys_make_inode(dir->d_inode, table);
 			if (!inode)
 				child = ERR_PTR(-ENOMEM);
 			else {
 				new->d_op = &proc_sys_dentry_operations;
 				d_add(new, inode);
 			}
 			if (child)
 				dput(new);
 			else
 				child = new;
 		}
 	}
 	if (!child || IS_ERR(child) || !child->d_inode)
 		goto end_instantiate;
 	inode = child->d_inode;
 	if (inode) {
 		ino  = inode->i_ino;
 		type = inode->i_mode >> 12;
 	}
 	dput(child);
 end_instantiate:
 	if (!ino)
 		ino= find_inode_number(dir, &qname);
 	if (!ino)
 		ino = 1;
 	return filldir(dirent, qname.name, qname.len, filp->f_pos, ino, type);
 }

 static int proc_sys_readdir(struct file *filp, void *dirent, filldir_t filldir)
 {
 	struct dentry *dentry = filp->f_dentry;
 	struct inode *inode = dentry->d_inode;
 	struct ctl_table_header *head = NULL;
 	struct ctl_table *table;
 	unsigned long pos;
 	int ret;

 	ret = -ENOTDIR;
 	if (!S_ISDIR(inode->i_mode))
 		goto out;

 	ret = 0;
 	/* Avoid a switch here: arm builds fail with missing __cmpdi2 */
 	if (filp->f_pos == 0) {
 		if (filldir(dirent, ".", 1, filp->f_pos,
 				inode->i_ino, DT_DIR) < 0)
 			goto out;
 		filp->f_pos++;
 	}
 	if (filp->f_pos == 1) {
 		if (filldir(dirent, "..", 2, filp->f_pos,
 				parent_ino(dentry), DT_DIR) < 0)
 			goto out;
 		filp->f_pos++;
 	}
 	pos = 2;

 	/* - Find each instance of the directory
 	 * - Read all entries in each instance
 	 * - Before returning an entry to user space lookup the entry
 	 *   by name and if I find a different entry don't return
 	 *   this one because it means it is a buried dup.
 	 * For sysctl this should only happen for directory entries.
 	 */
 	for (head = sysctl_head_next(NULL); head; head = sysctl_head_next(head)) {
 		table = proc_sys_lookup_table(dentry, head->ctl_table);

 		if (!table)
 			continue;

 		for (; table->ctl_name || table->procname; table++, pos++) {
 			/* Can't do anything without a proc name */
 			if (!table->procname)
 				continue;

 			if (pos < filp->f_pos)
 				continue;

 			if (proc_sys_fill_cache(filp, dirent, filldir, table) < 0)
 				goto out;
 			filp->f_pos = pos + 1;
 		}
 	}
 	ret = 1;
 out:
 	sysctl_head_finish(head);
 	return ret;
 }

 static int proc_sys_permission(struct inode *inode, int mask, struct nameidata *nd)
 {
 	/*
 	 * sysctl entries that are not writeable,
 	 * are _NOT_ writeable, capabilities or not.
 	 */
 	struct ctl_table_header *head;
 	struct ctl_table *table;
 	struct dentry *dentry;
 	int mode;
 	int depth;
 	int error;

 	head = NULL;
 	depth = PROC_I(inode)->fd;

 	/* First check the cached permissions, in case we don't have
 	 * enough information to lookup the sysctl table entry.
 	 */
 	error = -EACCES;
 	mode = inode->i_mode;

 	if (current->euid == 0)
 		mode >>= 6;
 	else if (in_group_p(0))
 		mode >>= 3;

 	if ((mode & mask & (MAY_READ|MAY_WRITE|MAY_EXEC)) == mask)
 		error = 0;

 	/* If we can't get a sysctl table entry the permission
 	 * checks on the cached mode will have to be enough.
 	 */
 	if (!nd || !depth)
 		goto out;

 	dentry = nd->dentry;
 	table = do_proc_sys_lookup(dentry->d_parent, &dentry->d_name, &head);

 	/* If the entry does not exist deny permission */
 	error = -EACCES;
 	if (!table)
 		goto out;

 	/* Use the permissions on the sysctl table entry */
 	error = sysctl_perm(table, mask);
 out:
 	sysctl_head_finish(head);
 	return error;
 }

 static int proc_sys_setattr(struct dentry *dentry, struct iattr *attr)
 {
 	struct inode *inode = dentry->d_inode;
 	int error;

 	if (attr->ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID))
 		return -EPERM;

 	error = inode_change_ok(inode, attr);
 	if (!error)
 		error = inode_setattr(inode, attr);

 	return error;
 }

 /* I'm lazy and don't distinguish between files and directories,
  * until access time.
  */
 static const struct file_operations proc_sys_file_operations = {
 	.read		= proc_sys_read,
 	.write		= proc_sys_write,
 	.readdir	= proc_sys_readdir,
 };

 static const struct inode_operations proc_sys_inode_operations = {
 	.lookup		= proc_sys_lookup,
 	.permission	= proc_sys_permission,
 	.setattr	= proc_sys_setattr,
 };

 static int proc_sys_revalidate(struct dentry *dentry, struct nameidata *nd)
 {
 	struct ctl_table_header *head;
 	struct ctl_table *table;
 	table = do_proc_sys_lookup(dentry->d_parent, &dentry->d_name, &head);
 	proc_sys_refresh_inode(dentry->d_inode, table);
 	sysctl_head_finish(head);
 	return !!table;
 }

 static struct dentry_operations proc_sys_dentry_operations = {
 	.d_revalidate	= proc_sys_revalidate,
 };

 static struct proc_dir_entry *proc_sys_root;

 int proc_sys_init(void)
 {
 	proc_sys_root = proc_mkdir("sys", NULL);
 	proc_sys_root->proc_iops = &proc_sys_inode_operations;
 	proc_sys_root->proc_fops = &proc_sys_file_operations;
 	proc_sys_root->nlink = 0;
 	return 0;
 }
	/*
	* /proc/sys support
	*/

	#include <linux/sysctl.h>
	#include <linux/proc_fs.h>
	#include <linux/security.h>
	#include "internal.h"

	static 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 void proc_sys_refresh_inode(struct inode inode, struct ctl_table table)
	{
	/* Refresh the cached information bits in the inode */
	if (table) {
	inode->i_uid = 0;
	inode->i_gid = 0;
	inode->i_mode = table->mode;
	if (table->proc_handler) {
	inode->i_mode \|= S_IFREG;
	inode->i_nlink = 1;
	} else {
	inode->i_mode \|= S_IFDIR;
	inode->i_nlink = 0; /* It is too hard to figure out */
	}
	}
	}

	static struct inode proc_sys_make_inode(struct inode dir, struct ctl_table *table)
	{
	struct inode *inode;
	struct proc_inode dir_ei, ei;
	int depth;

	inode = new_inode(dir->i_sb);
	if (!inode)
	goto out;

	/* A directory is always one deeper than it's parent */
	dir_ei = PROC_I(dir);
	depth = dir_ei->fd + 1;

	ei = PROC_I(inode);
	ei->fd = depth;
	inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
	inode->i_op = &proc_sys_inode_operations;
	inode->i_fop = &proc_sys_file_operations;
	inode->i_flags \|= S_PRIVATE; /* tell selinux to ignore this inode */
	proc_sys_refresh_inode(inode, table);
	out:
	return inode;
	}

	static struct dentry proc_sys_ancestor(struct dentry dentry, int depth)
	{
	for (;;) {
	struct proc_inode *ei;

	ei = PROC_I(dentry->d_inode);
	if (ei->fd == depth)
	break; /* found */

	dentry = dentry->d_parent;
	}
	return dentry;
	}

	static struct ctl_table proc_sys_lookup_table_one(struct ctl_table table,
	struct qstr *name)
	{
	int len;
	for ( ; table->ctl_name \|\| table->procname; table++) {

	if (!table->procname)
	continue;

	len = strlen(table->procname);
	if (len != name->len)
	continue;

	if (memcmp(table->procname, name->name, len) != 0)
	continue;

	/* I have a match */
	return table;
	}
	return NULL;
	}

	static struct ctl_table proc_sys_lookup_table(struct dentry dentry,
	struct ctl_table *table)
	{
	struct dentry *ancestor;
	struct proc_inode *ei;
	int depth, i;

	ei = PROC_I(dentry->d_inode);
	depth = ei->fd;

	if (depth == 0)
	return table;

	for (i = 1; table && (i <= depth); i++) {
	ancestor = proc_sys_ancestor(dentry, i);
	table = proc_sys_lookup_table_one(table, &ancestor->d_name);
	if (table)
	table = table->child;
	}
	return table;

	}
	static struct ctl_table proc_sys_lookup_entry(struct dentry dparent,
	struct qstr *name,
	struct ctl_table *table)
	{
	table = proc_sys_lookup_table(dparent, table);
	if (table)
	table = proc_sys_lookup_table_one(table, name);
	return table;
	}

	static struct ctl_table do_proc_sys_lookup(struct dentry parent,
	struct qstr *name,
	struct ctl_table_header **ptr)
	{
	struct ctl_table_header *head;
	struct ctl_table *table = NULL;

	for (head = sysctl_head_next(NULL); head;
	head = sysctl_head_next(head)) {
	table = proc_sys_lookup_entry(parent, name, head->ctl_table);
	if (table)
	break;
	}
	*ptr = head;
	return table;
	}

	static struct dentry proc_sys_lookup(struct inode dir, struct dentry *dentry,
	struct nameidata *nd)
	{
	struct ctl_table_header *head;
	struct inode *inode;
	struct dentry *err;
	struct ctl_table *table;

	err = ERR_PTR(-ENOENT);
	table = do_proc_sys_lookup(dentry->d_parent, &dentry->d_name, &head);
	if (!table)
	goto out;

	err = ERR_PTR(-ENOMEM);
	inode = proc_sys_make_inode(dir, table);
	if (!inode)
	goto out;

	err = NULL;
	dentry->d_op = &proc_sys_dentry_operations;
	d_add(dentry, inode);

	out:
	sysctl_head_finish(head);
	return err;
	}

	static ssize_t proc_sys_read(struct file filp, char __user buf,
	size_t count, loff_t *ppos)
	{
	struct dentry *dentry = filp->f_dentry;
	struct ctl_table_header *head;
	struct ctl_table *table;
	ssize_t error;
	size_t res;

	table = do_proc_sys_lookup(dentry->d_parent, &dentry->d_name, &head);
	/* Has the sysctl entry disappeared on us? */
	error = -ENOENT;
	if (!table)
	goto out;

	/* Has the sysctl entry been replaced by a directory? */
	error = -EISDIR;
	if (!table->proc_handler)
	goto out;

	/*
	* At this point we know that the sysctl was not unregistered
	* and won't be until we finish.
	*/
	error = -EPERM;
	if (sysctl_perm(table, MAY_READ))
	goto out;

	/* careful: calling conventions are nasty here */
	res = count;
	error = table->proc_handler(table, 0, filp, buf, &res, ppos);
	if (!error)
	error = res;
	out:
	sysctl_head_finish(head);

	return error;
	}

	static ssize_t proc_sys_write(struct file filp, const char __user buf,
	size_t count, loff_t *ppos)
	{
	struct dentry *dentry = filp->f_dentry;
	struct ctl_table_header *head;
	struct ctl_table *table;
	ssize_t error;
	size_t res;

	table = do_proc_sys_lookup(dentry->d_parent, &dentry->d_name, &head);
	/* Has the sysctl entry disappeared on us? */
	error = -ENOENT;
	if (!table)
	goto out;

	/* Has the sysctl entry been replaced by a directory? */
	error = -EISDIR;
	if (!table->proc_handler)
	goto out;

	/*
	* At this point we know that the sysctl was not unregistered
	* and won't be until we finish.
	*/
	error = -EPERM;
	if (sysctl_perm(table, MAY_WRITE))
	goto out;

	/* careful: calling conventions are nasty here */
	res = count;
	error = table->proc_handler(table, 1, filp, (char __user *)buf,
	&res, ppos);
	if (!error)
	error = res;
	out:
	sysctl_head_finish(head);

	return error;
	}


	static int proc_sys_fill_cache(struct file filp, void dirent,
	filldir_t filldir, struct ctl_table *table)
	{
	struct ctl_table_header *head;
	struct ctl_table *child_table = NULL;
	struct dentry child, dir = filp->f_path.dentry;
	struct inode *inode;
	struct qstr qname;
	ino_t ino = 0;
	unsigned type = DT_UNKNOWN;
	int ret;

	qname.name = table->procname;
	qname.len = strlen(table->procname);
	qname.hash = full_name_hash(qname.name, qname.len);

	/* Suppress duplicates.
	* Only fill a directory entry if it is the value that
	* an ordinary lookup of that name returns. Hide all
	* others.
	*
	* If we ever cache this translation in the dcache
	* I should do a dcache lookup first. But for now
	* it is just simpler not to.
	*/
	ret = 0;
	child_table = do_proc_sys_lookup(dir, &qname, &head);
	sysctl_head_finish(head);
	if (child_table != table)
	return 0;

	child = d_lookup(dir, &qname);
	if (!child) {
	struct dentry *new;
	new = d_alloc(dir, &qname);
	if (new) {
	inode = proc_sys_make_inode(dir->d_inode, table);
	if (!inode)
	child = ERR_PTR(-ENOMEM);
	else {
	new->d_op = &proc_sys_dentry_operations;
	d_add(new, inode);
	}
	if (child)
	dput(new);
	else
	child = new;
	}
	}
	if (!child \|\| IS_ERR(child) \|\| !child->d_inode)
	goto end_instantiate;
	inode = child->d_inode;
	if (inode) {
	ino = inode->i_ino;
	type = inode->i_mode >> 12;
	}
	dput(child);
	end_instantiate:
	if (!ino)
	ino= find_inode_number(dir, &qname);
	if (!ino)
	ino = 1;
	return filldir(dirent, qname.name, qname.len, filp->f_pos, ino, type);
	}

	static int proc_sys_readdir(struct file filp, void dirent, filldir_t filldir)
	{
	struct dentry *dentry = filp->f_dentry;
	struct inode *inode = dentry->d_inode;
	struct ctl_table_header *head = NULL;
	struct ctl_table *table;
	unsigned long pos;
	int ret;

	ret = -ENOTDIR;
	if (!S_ISDIR(inode->i_mode))
	goto out;

	ret = 0;
	/* Avoid a switch here: arm builds fail with missing __cmpdi2 */
	if (filp->f_pos == 0) {
	if (filldir(dirent, ".", 1, filp->f_pos,
	inode->i_ino, DT_DIR) < 0)
	goto out;
	filp->f_pos++;
	}
	if (filp->f_pos == 1) {
	if (filldir(dirent, "..", 2, filp->f_pos,
	parent_ino(dentry), DT_DIR) < 0)
	goto out;
	filp->f_pos++;
	}
	pos = 2;

	/* - Find each instance of the directory
	* - Read all entries in each instance
	* - Before returning an entry to user space lookup the entry
	* by name and if I find a different entry don't return
	* this one because it means it is a buried dup.
	* For sysctl this should only happen for directory entries.
	*/
	for (head = sysctl_head_next(NULL); head; head = sysctl_head_next(head)) {
	table = proc_sys_lookup_table(dentry, head->ctl_table);

	if (!table)
	continue;

	for (; table->ctl_name \|\| table->procname; table++, pos++) {
	/* Can't do anything without a proc name */
	if (!table->procname)
	continue;

	if (pos < filp->f_pos)
	continue;

	if (proc_sys_fill_cache(filp, dirent, filldir, table) < 0)
	goto out;
	filp->f_pos = pos + 1;
	}
	}
	ret = 1;
	out:
	sysctl_head_finish(head);
	return ret;
	}

	static int proc_sys_permission(struct inode inode, int mask, struct nameidata nd)
	{
	/*
	* sysctl entries that are not writeable,
	* are _NOT_ writeable, capabilities or not.
	*/
	struct ctl_table_header *head;
	struct ctl_table *table;
	struct dentry *dentry;
	int mode;
	int depth;
	int error;

	head = NULL;
	depth = PROC_I(inode)->fd;

	/* First check the cached permissions, in case we don't have
	* enough information to lookup the sysctl table entry.
	*/
	error = -EACCES;
	mode = inode->i_mode;

	if (current->euid == 0)
	mode >>= 6;
	else if (in_group_p(0))
	mode >>= 3;

	if ((mode & mask & (MAY_READ\|MAY_WRITE\|MAY_EXEC)) == mask)
	error = 0;

	/* If we can't get a sysctl table entry the permission
	* checks on the cached mode will have to be enough.
	*/
	if (!nd \|\| !depth)
	goto out;

	dentry = nd->dentry;
	table = do_proc_sys_lookup(dentry->d_parent, &dentry->d_name, &head);

	/* If the entry does not exist deny permission */
	error = -EACCES;
	if (!table)
	goto out;

	/* Use the permissions on the sysctl table entry */
	error = sysctl_perm(table, mask);
	out:
	sysctl_head_finish(head);
	return error;
	}

	static int proc_sys_setattr(struct dentry dentry, struct iattr attr)
	{
	struct inode *inode = dentry->d_inode;
	int error;

	if (attr->ia_valid & (ATTR_MODE \| ATTR_UID \| ATTR_GID))
	return -EPERM;

	error = inode_change_ok(inode, attr);
	if (!error)
	error = inode_setattr(inode, attr);

	return error;
	}

	/* I'm lazy and don't distinguish between files and directories,
	* until access time.
	*/
	static const struct file_operations proc_sys_file_operations = {
	.read = proc_sys_read,
	.write = proc_sys_write,
	.readdir = proc_sys_readdir,
	};

	static const struct inode_operations proc_sys_inode_operations = {
	.lookup = proc_sys_lookup,
	.permission = proc_sys_permission,
	.setattr = proc_sys_setattr,
	};

	static int proc_sys_revalidate(struct dentry dentry, struct nameidata nd)
	{
	struct ctl_table_header *head;
	struct ctl_table *table;
	table = do_proc_sys_lookup(dentry->d_parent, &dentry->d_name, &head);
	proc_sys_refresh_inode(dentry->d_inode, table);
	sysctl_head_finish(head);
	return !!table;
	}

	static struct dentry_operations proc_sys_dentry_operations = {
	.d_revalidate = proc_sys_revalidate,
	};

	static struct proc_dir_entry *proc_sys_root;

	int proc_sys_init(void)
	{
	proc_sys_root = proc_mkdir("sys", NULL);
	proc_sys_root->proc_iops = &proc_sys_inode_operations;
	proc_sys_root->proc_fops = &proc_sys_file_operations;
	proc_sys_root->nlink = 0;
	return 0;
	}