sysctl: Create local copies of directory names used in paths

[mirror_ubuntu-bionic-kernel.git] / fs / proc / proc_sysctl.c

/*
 * /proc/sys support
 */
#include <linux/init.h>
#include <linux/sysctl.h>
#include <linux/poll.h>
#include <linux/proc_fs.h>
#include <linux/security.h>
#include <linux/namei.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;

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[1];
static struct ctl_table_root sysctl_table_root;
static struct ctl_table_header root_table_header = {
        {{.count = 1,
        .ctl_table = root_table,
        .ctl_entry = LIST_HEAD_INIT(sysctl_table_root.default_set.list),}},
        .root = &sysctl_table_root,
        .set = &sysctl_table_root.default_set,
};
static struct ctl_table_root sysctl_table_root = {
        .root_list = LIST_HEAD_INIT(sysctl_table_root.root_list),
        .default_set.list = LIST_HEAD_INIT(root_table_header.ctl_entry),
};

static DEFINE_SPINLOCK(sysctl_lock);

/* 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);
}

/* 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);
                spin_lock(&sysctl_lock);
        } else {
                /* anything non-NULL; we'll never dereference it */
                p->unregistering = ERR_PTR(-EINVAL);
        }
        /*
         * do not remove from the list until nobody holds it; walking the
         * list in do_sysctl() relies on that.
         */
        list_del_init(&p->ctl_entry);
}

static void sysctl_head_get(struct ctl_table_header *head)
{
        spin_lock(&sysctl_lock);
        head->count++;
        spin_unlock(&sysctl_lock);
}

void sysctl_head_put(struct ctl_table_header *head)
{
        spin_lock(&sysctl_lock);
        if (!--head->count)
                kfree_rcu(head, rcu);
        spin_unlock(&sysctl_lock);
}

static struct ctl_table_header *sysctl_head_grab(struct ctl_table_header *head)
{
        if (!head)
                BUG();
        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 nsproxy *namespaces)
{
        struct ctl_table_set *set = &root->default_set;
        if (root->lookup)
                set = root->lookup(root, namespaces);
        return set;
}

static struct list_head *
lookup_header_list(struct ctl_table_root *root, struct nsproxy *namespaces)
{
        struct ctl_table_set *set = lookup_header_set(root, namespaces);
        return &set->list;
}

static struct ctl_table_header *__sysctl_head_next(struct nsproxy *namespaces,
                                                struct ctl_table_header *prev)
{
        struct ctl_table_root *root;
        struct list_head *header_list;
        struct ctl_table_header *head;
        struct list_head *tmp;

        spin_lock(&sysctl_lock);
        if (prev) {
                head = prev;
                tmp = &prev->ctl_entry;
                unuse_table(prev);
                goto next;
        }
        tmp = &root_table_header.ctl_entry;
        for (;;) {
                head = list_entry(tmp, struct ctl_table_header, ctl_entry);

                if (!use_table(head))
                        goto next;
                spin_unlock(&sysctl_lock);
                return head;
        next:
                root = head->root;
                tmp = tmp->next;
                header_list = lookup_header_list(root, namespaces);
                if (tmp != header_list)
                        continue;

                do {
                        root = list_entry(root->root_list.next,
                                        struct ctl_table_root, root_list);
                        if (root == &sysctl_table_root)
                                goto out;
                        header_list = lookup_header_list(root, namespaces);
                } while (list_empty(header_list));
                tmp = header_list->next;
        }
out:
        spin_unlock(&sysctl_lock);
        return NULL;
}

static struct ctl_table_header *sysctl_head_next(struct ctl_table_header *prev)
{
        return __sysctl_head_next(current->nsproxy, prev);
}

void register_sysctl_root(struct ctl_table_root *root)
{
        spin_lock(&sysctl_lock);
        list_add_tail(&root->root_list, &sysctl_table_root.root_list);
        spin_unlock(&sysctl_lock);
}

/*
 * 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 (!current_euid())
                mode >>= 6;
        else if (in_egroup_p(0))
                mode >>= 3;
        if ((op & ~mode & (MAY_READ|MAY_WRITE|MAY_EXEC)) == 0)
                return 0;
        return -EACCES;
}

static int sysctl_perm(struct ctl_table_root *root, struct ctl_table *table, int op)
{
        int mode;

        if (root->permissions)
                mode = root->permissions(root, current->nsproxy, table);
        else
                mode = table->mode;

        return test_perm(mode, op);
}

static void sysctl_set_parent(struct ctl_table *parent, struct ctl_table *table)
{
        for (; table->procname; table++) {
                table->parent = parent;
                if (table->child)
                        sysctl_set_parent(table, table->child);
        }
}


static struct inode *proc_sys_make_inode(struct super_block *sb,
                struct ctl_table_header *head, struct ctl_table *table)
{
        struct inode *inode;
        struct proc_inode *ei;

        inode = new_inode(sb);
        if (!inode)
                goto out;

        inode->i_ino = get_next_ino();

        sysctl_head_get(head);
        ei = PROC_I(inode);
        ei->sysctl = head;
        ei->sysctl_entry = table;

        inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
        inode->i_mode = table->mode;
        if (!table->child) {
                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;
        }
out:
        return inode;
}

static struct ctl_table *find_in_table(struct ctl_table *p, struct qstr *name)
{
        for ( ; p->procname; p++) {
                if (strlen(p->procname) != name->len)
                        continue;

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

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

static struct ctl_table_header *grab_header(struct inode *inode)
{
        if (PROC_I(inode)->sysctl)
                return sysctl_head_grab(PROC_I(inode)->sysctl);
        else
                return sysctl_head_next(NULL);
}

static struct dentry *proc_sys_lookup(struct inode *dir, struct dentry *dentry,
                                        struct nameidata *nd)
{
        struct ctl_table_header *head = grab_header(dir);
        struct ctl_table *table = PROC_I(dir)->sysctl_entry;
        struct ctl_table_header *h = NULL;
        struct qstr *name = &dentry->d_name;
        struct ctl_table *p;
        struct inode *inode;
        struct dentry *err = ERR_PTR(-ENOENT);

        if (IS_ERR(head))
                return ERR_CAST(head);

        if (table && !table->child) {
                WARN_ON(1);
                goto out;
        }

        table = table ? table->child : head->ctl_table;

        p = find_in_table(table, name);
        if (!p) {
                for (h = sysctl_head_next(NULL); h; h = sysctl_head_next(h)) {
                        if (h->attached_to != table)
                                continue;
                        p = find_in_table(h->attached_by, name);
                        if (p)
                                break;
                }
        }

        if (!p)
                goto out;

        err = ERR_PTR(-ENOMEM);
        inode = proc_sys_make_inode(dir->i_sb, h ? h : head, p);
        if (h)
                sysctl_head_finish(h);

        if (!inode)
                goto out;

        err = NULL;
        d_set_d_op(dentry, &proc_sys_dentry_operations);
        d_add(dentry, inode);

out:
        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 = filp->f_path.dentry->d_inode;
        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->root, 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 *table = PROC_I(inode)->sysctl_entry;

        if (table->poll)
                filp->private_data = proc_sys_poll_event(table->poll);

        return 0;
}

static unsigned int proc_sys_poll(struct file *filp, poll_table *wait)
{
        struct inode *inode = filp->f_path.dentry->d_inode;
        struct ctl_table *table = PROC_I(inode)->sysctl_entry;
        unsigned long event = (unsigned long)filp->private_data;
        unsigned int ret = DEFAULT_POLLMASK;

        if (!table->proc_handler)
                goto out;

        if (!table->poll)
                goto out;

        poll_wait(filp, &table->poll->wait, wait);

        if (event != atomic_read(&table->poll->event)) {
                filp->private_data = proc_sys_poll_event(table->poll);
                ret = POLLIN | POLLRDNORM | POLLERR | POLLPRI;
        }

out:
        return ret;
}

static int proc_sys_fill_cache(struct file *filp, void *dirent,
                                filldir_t filldir,
                                struct ctl_table_header *head,
                                struct ctl_table *table)
{
        struct dentry *child, *dir = filp->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(qname.name, qname.len);

        child = d_lookup(dir, &qname);
        if (!child) {
                child = d_alloc(dir, &qname);
                if (child) {
                        inode = proc_sys_make_inode(dir->d_sb, head, table);
                        if (!inode) {
                                dput(child);
                                return -ENOMEM;
                        } else {
                                d_set_d_op(child, &proc_sys_dentry_operations);
                                d_add(child, inode);
                        }
                } else {
                        return -ENOMEM;
                }
        }
        inode = child->d_inode;
        ino  = inode->i_ino;
        type = inode->i_mode >> 12;
        dput(child);
        return !!filldir(dirent, qname.name, qname.len, filp->f_pos, ino, type);
}

static int scan(struct ctl_table_header *head, ctl_table *table,
                unsigned long *pos, struct file *file,
                void *dirent, filldir_t filldir)
{

        for (; table->procname; table++, (*pos)++) {
                int res;

                if (*pos < file->f_pos)
                        continue;

                res = proc_sys_fill_cache(file, dirent, filldir, head, table);
                if (res)
                        return res;

                file->f_pos = *pos + 1;
        }
        return 0;
}

static int proc_sys_readdir(struct file *filp, void *dirent, filldir_t filldir)
{
        struct dentry *dentry = filp->f_path.dentry;
        struct inode *inode = dentry->d_inode;
        struct ctl_table_header *head = grab_header(inode);
        struct ctl_table *table = PROC_I(inode)->sysctl_entry;
        struct ctl_table_header *h = NULL;
        unsigned long pos;
        int ret = -EINVAL;

        if (IS_ERR(head))
                return PTR_ERR(head);

        if (table && !table->child) {
                WARN_ON(1);
                goto out;
        }

        table = table ? table->child : head->ctl_table;

        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;

        ret = scan(head, table, &pos, filp, dirent, filldir);
        if (ret)
                goto out;

        for (h = sysctl_head_next(NULL); h; h = sysctl_head_next(h)) {
                if (h->attached_to != table)
                        continue;
                ret = scan(h, h->attached_by, &pos, filp, dirent, filldir);
                if (ret) {
                        sysctl_head_finish(h);
                        break;
                }
        }
        ret = 1;
out:
        sysctl_head_finish(head);
        return ret;
}

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->root, 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 = 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)
                return error;

        if ((attr->ia_valid & ATTR_SIZE) &&
            attr->ia_size != i_size_read(inode)) {
                error = vmtruncate(inode, attr->ia_size);
                if (error)
                        return error;
        }

        setattr_copy(inode, attr);
        mark_inode_dirty(inode);
        return 0;
}

static int proc_sys_getattr(struct vfsmount *mnt, struct dentry *dentry, struct kstat *stat)
{
        struct inode *inode = dentry->d_inode;
        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,
        .readdir        = 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, struct nameidata *nd)
{
        if (nd->flags & LOOKUP_RCU)
                return -ECHILD;
        return !PROC_I(dentry->d_inode)->sysctl->unregistering;
}

static int proc_sys_delete(const struct dentry *dentry)
{
        return !!PROC_I(dentry->d_inode)->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 *parent,
                const struct inode *pinode,
                const struct dentry *dentry, const struct inode *inode,
                unsigned int len, const char *str, const struct qstr *name)
{
        struct ctl_table_header *head;
        /* Although proc doesn't have negative dentries, rcu-walk means
         * that inode here can be NULL */
        /* AV: can it, indeed? */
        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_table *is_branch_in(struct ctl_table *branch,
                                      struct ctl_table *table)
{
        struct ctl_table *p;
        const char *s = branch->procname;

        /* branch should have named subdirectory as its first element */
        if (!s || !branch->child)
                return NULL;

        /* ... and nothing else */
        if (branch[1].procname)
                return NULL;

        /* table should contain subdirectory with the same name */
        for (p = table; p->procname; p++) {
                if (!p->child)
                        continue;
                if (p->procname && strcmp(p->procname, s) == 0)
                        return p;
        }
        return NULL;
}

/* see if attaching q to p would be an improvement */
static void try_attach(struct ctl_table_header *p, struct ctl_table_header *q)
{
        struct ctl_table *to = p->ctl_table, *by = q->ctl_table;
        struct ctl_table *next;
        int is_better = 0;
        int not_in_parent = !p->attached_by;

        while ((next = is_branch_in(by, to)) != NULL) {
                if (by == q->attached_by)
                        is_better = 1;
                if (to == p->attached_by)
                        not_in_parent = 1;
                by = by->child;
                to = next->child;
        }

        if (is_better && not_in_parent) {
                q->attached_by = by;
                q->attached_to = to;
                q->parent = p;
        }
}

#ifdef CONFIG_SYSCTL_SYSCALL_CHECK
static int sysctl_depth(struct ctl_table *table)
{
        struct ctl_table *tmp;
        int depth;

        depth = 0;
        for (tmp = table; tmp->parent; tmp = tmp->parent)
                depth++;

        return depth;
}

static struct ctl_table *sysctl_parent(struct ctl_table *table, int n)
{
        int i;

        for (i = 0; table && i < n; i++)
                table = table->parent;

        return table;
}


static void sysctl_print_path(struct ctl_table *table)
{
        struct ctl_table *tmp;
        int depth, i;
        depth = sysctl_depth(table);
        if (table->procname) {
                for (i = depth; i >= 0; i--) {
                        tmp = sysctl_parent(table, i);
                        printk("/%s", tmp->procname?tmp->procname:"");
                }
        }
        printk(" ");
}

static struct ctl_table *sysctl_check_lookup(struct nsproxy *namespaces,
                                                struct ctl_table *table)
{
        struct ctl_table_header *head;
        struct ctl_table *ref, *test;
        int depth, cur_depth;

        depth = sysctl_depth(table);

        for (head = __sysctl_head_next(namespaces, NULL); head;
             head = __sysctl_head_next(namespaces, head)) {
                cur_depth = depth;
                ref = head->ctl_table;
repeat:
                test = sysctl_parent(table, cur_depth);
                for (; ref->procname; ref++) {
                        int match = 0;
                        if (cur_depth && !ref->child)
                                continue;

                        if (test->procname && ref->procname &&
                            (strcmp(test->procname, ref->procname) == 0))
                                        match++;

                        if (match) {
                                if (cur_depth != 0) {
                                        cur_depth--;
                                        ref = ref->child;
                                        goto repeat;
                                }
                                goto out;
                        }
                }
        }
        ref = NULL;
out:
        sysctl_head_finish(head);
        return ref;
}

static void set_fail(const char **fail, struct ctl_table *table, const char *str)
{
        if (*fail) {
                printk(KERN_ERR "sysctl table check failed: ");
                sysctl_print_path(table);
                printk(" %s\n", *fail);
                dump_stack();
        }
        *fail = str;
}

static void sysctl_check_leaf(struct nsproxy *namespaces,
                                struct ctl_table *table, const char **fail)
{
        struct ctl_table *ref;

        ref = sysctl_check_lookup(namespaces, table);
        if (ref && (ref != table))
                set_fail(fail, table, "Sysctl already exists");
}

static int sysctl_check_table(struct nsproxy *namespaces, struct ctl_table *table)
{
        int error = 0;
        for (; table->procname; table++) {
                const char *fail = NULL;

                if (table->parent) {
                        if (!table->parent->procname)
                                set_fail(&fail, table, "Parent without procname");
                }
                if (table->child) {
                        if (table->data)
                                set_fail(&fail, table, "Directory with data?");
                        if (table->maxlen)
                                set_fail(&fail, table, "Directory with maxlen?");
                        if ((table->mode & (S_IRUGO|S_IXUGO)) != table->mode)
                                set_fail(&fail, table, "Writable sysctl directory");
                        if (table->proc_handler)
                                set_fail(&fail, table, "Directory with proc_handler");
                        if (table->extra1)
                                set_fail(&fail, table, "Directory with extra1");
                        if (table->extra2)
                                set_fail(&fail, table, "Directory with extra2");
                } else {
                        if ((table->proc_handler == proc_dostring) ||
                            (table->proc_handler == proc_dointvec) ||
                            (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)
                                        set_fail(&fail, table, "No data");
                                if (!table->maxlen)
                                        set_fail(&fail, table, "No maxlen");
                        }
#ifdef CONFIG_PROC_SYSCTL
                        if (!table->proc_handler)
                                set_fail(&fail, table, "No proc_handler");
#endif
                        sysctl_check_leaf(namespaces, table, &fail);
                }
                if (table->mode > 0777)
                        set_fail(&fail, table, "bogus .mode");
                if (fail) {
                        set_fail(&fail, table, NULL);
                        error = -EINVAL;
                }
                if (table->child)
                        error |= sysctl_check_table(namespaces, table->child);
        }
        return error;
}
#endif /* CONFIG_SYSCTL_SYSCALL_CHECK */

/**
 * __register_sysctl_paths - register a sysctl hierarchy
 * @root: List of sysctl headers to register on
 * @namespaces: Data to compute which lists of sysctl entries are visible
 * @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, and for sysctl(2)
 *
 * child - a pointer to the child sysctl table if this entry is a directory, or
 *         %NULL.
 *
 * proc_handler - the text handler routine (described below)
 *
 * de - for internal use by the sysctl routines
 *
 * 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.
 *
 * sysctl(2) can automatically manage read and write requests through
 * the sysctl table.  The data and maxlen fields of the ctl_table
 * struct enable minimal validation of the values being written to be
 * performed, and the mode field allows minimal authentication.
 *
 * There must be a proc_handler routine for any terminal nodes
 * mirrored under /proc/sys (non-terminals are handled by a built-in
 * directory handler).  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_paths(
        struct ctl_table_root *root,
        struct nsproxy *namespaces,
        const struct ctl_path *path, struct ctl_table *table)
{
        struct ctl_table_header *header;
        struct ctl_table *new, **prevp;
        unsigned int n, npath;
        struct ctl_table_set *set;
        size_t path_bytes = 0;
        char *new_name;

        /* Count the path components */
        for (npath = 0; path[npath].procname; ++npath)
                path_bytes += strlen(path[npath].procname) + 1;

        /*
         * For each path component, allocate a 2-element ctl_table array.
         * The first array element will be filled with the sysctl entry
         * for this, the second will be the sentinel (procname == 0).
         *
         * We allocate everything in one go so that we don't have to
         * worry about freeing additional memory in unregister_sysctl_table.
         */
        header = kzalloc(sizeof(struct ctl_table_header) + path_bytes +
                         (2 * npath * sizeof(struct ctl_table)), GFP_KERNEL);
        if (!header)
                return NULL;

        new = (struct ctl_table *) (header + 1);
        new_name = (char *)(new + (2 * npath));

        /* Now connect the dots */
        prevp = &header->ctl_table;
        for (n = 0; n < npath; ++n, ++path) {
                /* Copy the procname */
                strcpy(new_name, path->procname);
                new->procname = new_name;
                new->mode     = 0555;

                *prevp = new;
                prevp = &new->child;

                new += 2;
                new_name += strlen(new_name) + 1;
        }
        *prevp = table;
        header->ctl_table_arg = table;

        INIT_LIST_HEAD(&header->ctl_entry);
        header->used = 0;
        header->unregistering = NULL;
        header->root = root;
        sysctl_set_parent(NULL, header->ctl_table);
        header->count = 1;
#ifdef CONFIG_SYSCTL_SYSCALL_CHECK
        if (sysctl_check_table(namespaces, header->ctl_table)) {
                kfree(header);
                return NULL;
        }
#endif
        spin_lock(&sysctl_lock);
        header->set = lookup_header_set(root, namespaces);
        header->attached_by = header->ctl_table;
        header->attached_to = root_table;
        header->parent = &root_table_header;
        set = header->set;
        root = header->root;
        for (;;) {
                struct ctl_table_header *p;
                list_for_each_entry(p, &set->list, ctl_entry) {
                        if (p->unregistering)
                                continue;
                        try_attach(p, header);
                }
                if (root == &sysctl_table_root)
                        break;
                root = list_entry(root->root_list.prev,
                                  struct ctl_table_root, root_list);
                set = lookup_header_set(root, namespaces);
        }
        header->parent->count++;
        list_add_tail(&header->ctl_entry, &header->set->list);
        spin_unlock(&sysctl_lock);

        return header;
}

/**
 * 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, current->nsproxy,
                                        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);

/**
 * 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)
{
        might_sleep();

        if (header == NULL)
                return;

        spin_lock(&sysctl_lock);
        start_unregistering(header);
        if (!--header->parent->count) {
                WARN_ON(1);
                kfree_rcu(header->parent, rcu);
        }
        if (!--header->count)
                kfree_rcu(header, rcu);
        spin_unlock(&sysctl_lock);
}
EXPORT_SYMBOL(unregister_sysctl_table);

void setup_sysctl_set(struct ctl_table_set *p,
        int (*is_seen)(struct ctl_table_set *))
{
        INIT_LIST_HEAD(&p->list);
        p->is_seen = is_seen;
}

void retire_sysctl_set(struct ctl_table_set *set)
{
        WARN_ON(!list_empty(&set->list));
}

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();
}