// 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 <linux/bpf-cgroup.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;

/* shared constants to be used in various sysctls */
const int sysctl_vals[] = { 0, 1, INT_MAX };
EXPORT_SYMBOL(sysctl_vals);

/* 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_invalidate_dcache(struct ctl_table_header *head)
{
        proc_invalidate_siblings_dcache(&head->inodes, &sysctl_lock);
}

/* 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);
        }
        /*
         * Invalidate dentries for unregistered sysctls: namespaced sysctls
         * can have duplicate names and contaminate dcache very badly.
         */
        proc_sys_invalidate_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->sibling_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);
        else {
                inode->i_uid = GLOBAL_ROOT_UID;
                inode->i_gid = GLOBAL_ROOT_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)->sibling_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;
        void *new_buf = NULL;
        ssize_t error;

        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;

        error = BPF_CGROUP_RUN_PROG_SYSCTL(head, table, write, buf, &count,
                                           ppos, &new_buf);
        if (error)
                goto out;

        /* careful: calling conventions are nasty here */
        if (new_buf) {
                mm_segment_t old_fs;

                old_fs = get_fs();
                set_fs(KERNEL_DS);
                error = table->proc_handler(table, write, (void __user *)new_buf,
                                            &count, ppos);
                set_fs(old_fs);
                kfree(new_buf);
        } else {
                error = table->proc_handler(table, write, buf, &count, ppos);
        }

        if (!error)
                error = count;
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;

        if (parent) {
                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_dir_ops = &proc_sys_dir_file_operations;
        proc_sys_root->nlink = 0;

        return sysctl_init();
}