// SPDX-License-Identifier: GPL-2.0-only
/*
 * proc/fs/generic.c --- generic routines for the proc-fs
 *
 * This file contains generic proc-fs routines for handling
 * directories and files.
 * 
 * Copyright (C) 1991, 1992 Linus Torvalds.
 * Copyright (C) 1997 Theodore Ts'o
 */

#include <linux/cache.h>
#include <linux/errno.h>
#include <linux/time.h>
#include <linux/proc_fs.h>
#include <linux/stat.h>
#include <linux/mm.h>
#include <linux/module.h>
#include <linux/namei.h>
#include <linux/slab.h>
#include <linux/printk.h>
#include <linux/mount.h>
#include <linux/init.h>
#include <linux/idr.h>
#include <linux/bitops.h>
#include <linux/spinlock.h>
#include <linux/completion.h>
#include <linux/uaccess.h>
#include <linux/seq_file.h>

#include "internal.h"

static DEFINE_RWLOCK(proc_subdir_lock);

struct kmem_cache *proc_dir_entry_cache __ro_after_init;

void pde_free(struct proc_dir_entry *pde)
{
        if (S_ISLNK(pde->mode))
                kfree(pde->data);
        if (pde->name != pde->inline_name)
                kfree(pde->name);
        kmem_cache_free(proc_dir_entry_cache, pde);
}

static int proc_match(const char *name, struct proc_dir_entry *de, unsigned int len)
{
        if (len < de->namelen)
                return -1;
        if (len > de->namelen)
                return 1;

        return memcmp(name, de->name, len);
}

static struct proc_dir_entry *pde_subdir_first(struct proc_dir_entry *dir)
{
        return rb_entry_safe(rb_first(&dir->subdir), struct proc_dir_entry,
                             subdir_node);
}

static struct proc_dir_entry *pde_subdir_next(struct proc_dir_entry *dir)
{
        return rb_entry_safe(rb_next(&dir->subdir_node), struct proc_dir_entry,
                             subdir_node);
}

static struct proc_dir_entry *pde_subdir_find(struct proc_dir_entry *dir,
                                              const char *name,
                                              unsigned int len)
{
        struct rb_node *node = dir->subdir.rb_node;

        while (node) {
                struct proc_dir_entry *de = rb_entry(node,
                                                     struct proc_dir_entry,
                                                     subdir_node);
                int result = proc_match(name, de, len);

                if (result < 0)
                        node = node->rb_left;
                else if (result > 0)
                        node = node->rb_right;
                else
                        return de;
        }
        return NULL;
}

static bool pde_subdir_insert(struct proc_dir_entry *dir,
                              struct proc_dir_entry *de)
{
        struct rb_root *root = &dir->subdir;
        struct rb_node **new = &root->rb_node, *parent = NULL;

        /* Figure out where to put new node */
        while (*new) {
                struct proc_dir_entry *this = rb_entry(*new,
                                                       struct proc_dir_entry,
                                                       subdir_node);
                int result = proc_match(de->name, this, de->namelen);

                parent = *new;
                if (result < 0)
                        new = &(*new)->rb_left;
                else if (result > 0)
                        new = &(*new)->rb_right;
                else
                        return false;
        }

        /* Add new node and rebalance tree. */
        rb_link_node(&de->subdir_node, parent, new);
        rb_insert_color(&de->subdir_node, root);
        return true;
}

static int proc_notify_change(struct mnt_idmap *idmap,
                              struct dentry *dentry, struct iattr *iattr)
{
        struct inode *inode = d_inode(dentry);
        struct proc_dir_entry *de = PDE(inode);
        int error;

        error = setattr_prepare(&nop_mnt_idmap, dentry, iattr);
        if (error)
                return error;

        setattr_copy(&nop_mnt_idmap, inode, iattr);

        proc_set_user(de, inode->i_uid, inode->i_gid);
        de->mode = inode->i_mode;
        return 0;
}

static int proc_getattr(struct mnt_idmap *idmap,
                        const struct path *path, struct kstat *stat,
                        u32 request_mask, unsigned int query_flags)
{
        struct inode *inode = d_inode(path->dentry);
        struct proc_dir_entry *de = PDE(inode);
        if (de) {
                nlink_t nlink = READ_ONCE(de->nlink);
                if (nlink > 0) {
                        set_nlink(inode, nlink);
                }
        }

        generic_fillattr(&nop_mnt_idmap, request_mask, inode, stat);
        return 0;
}

static const struct inode_operations proc_file_inode_operations = {
        .setattr        = proc_notify_change,
};

/*
 * This function parses a name such as "tty/driver/serial", and
 * returns the struct proc_dir_entry for "/proc/tty/driver", and
 * returns "serial" in residual.
 */
static int __xlate_proc_name(const char *name, struct proc_dir_entry **ret,
                             const char **residual)
{
        const char              *cp = name, *next;
        struct proc_dir_entry   *de;

        de = *ret ?: &proc_root;
        while ((next = strchr(cp, '/')) != NULL) {
                de = pde_subdir_find(de, cp, next - cp);
                if (!de) {
                        WARN(1, "name '%s'\n", name);
                        return -ENOENT;
                }
                cp = next + 1;
        }
        *residual = cp;
        *ret = de;
        return 0;
}

static int xlate_proc_name(const char *name, struct proc_dir_entry **ret,
                           const char **residual)
{
        int rv;

        read_lock(&proc_subdir_lock);
        rv = __xlate_proc_name(name, ret, residual);
        read_unlock(&proc_subdir_lock);
        return rv;
}

static DEFINE_IDA(proc_inum_ida);

#define PROC_DYNAMIC_FIRST 0xF0000000U

/*
 * Return an inode number between PROC_DYNAMIC_FIRST and
 * 0xffffffff, or zero on failure.
 */
int proc_alloc_inum(unsigned int *inum)
{
        int i;

        i = ida_alloc_max(&proc_inum_ida, UINT_MAX - PROC_DYNAMIC_FIRST,
                          GFP_KERNEL);
        if (i < 0)
                return i;

        *inum = PROC_DYNAMIC_FIRST + (unsigned int)i;
        return 0;
}

void proc_free_inum(unsigned int inum)
{
        ida_free(&proc_inum_ida, inum - PROC_DYNAMIC_FIRST);
}

static int proc_misc_d_revalidate(struct inode *dir, const struct qstr *name,
                                  struct dentry *dentry, unsigned int flags)
{
        if (flags & LOOKUP_RCU)
                return -ECHILD;

        if (atomic_read(&PDE(d_inode(dentry))->in_use) < 0)
                return 0; /* revalidate */
        return 1;
}

static int proc_misc_d_delete(const struct dentry *dentry)
{
        return atomic_read(&PDE(d_inode(dentry))->in_use) < 0;
}

static const struct dentry_operations proc_misc_dentry_ops = {
        .d_revalidate   = proc_misc_d_revalidate,
        .d_delete       = proc_misc_d_delete,
};

/*
 * Don't create negative dentries here, return -ENOENT by hand
 * instead.
 */
struct dentry *proc_lookup_de(struct inode *dir, struct dentry *dentry,
                              struct proc_dir_entry *de)
{
        struct inode *inode;

        read_lock(&proc_subdir_lock);
        de = pde_subdir_find(de, dentry->d_name.name, dentry->d_name.len);
        if (de) {
                pde_get(de);
                read_unlock(&proc_subdir_lock);
                inode = proc_get_inode(dir->i_sb, de);
                if (!inode)
                        return ERR_PTR(-ENOMEM);
                if (de->flags & PROC_ENTRY_FORCE_LOOKUP)
                        return d_splice_alias_ops(inode, dentry,
                                                  &proc_net_dentry_ops);
                return d_splice_alias_ops(inode, dentry,
                                          &proc_misc_dentry_ops);
        }
        read_unlock(&proc_subdir_lock);
        return ERR_PTR(-ENOENT);
}

struct dentry *proc_lookup(struct inode *dir, struct dentry *dentry,
                unsigned int flags)
{
        struct proc_fs_info *fs_info = proc_sb_info(dir->i_sb);

        if (fs_info->pidonly == PROC_PIDONLY_ON)
                return ERR_PTR(-ENOENT);

        return proc_lookup_de(dir, dentry, PDE(dir));
}

/*
 * This returns non-zero if at EOF, so that the /proc
 * root directory can use this and check if it should
 * continue with the <pid> entries..
 *
 * Note that the VFS-layer doesn't care about the return
 * value of the readdir() call, as long as it's non-negative
 * for success..
 */
int proc_readdir_de(struct file *file, struct dir_context *ctx,
                    struct proc_dir_entry *de)
{
        int i;

        if (!dir_emit_dots(file, ctx))
                return 0;

        i = ctx->pos - 2;
        read_lock(&proc_subdir_lock);
        de = pde_subdir_first(de);
        for (;;) {
                if (!de) {
                        read_unlock(&proc_subdir_lock);
                        return 0;
                }
                if (!i)
                        break;
                de = pde_subdir_next(de);
                i--;
        }

        do {
                struct proc_dir_entry *next;
                pde_get(de);
                read_unlock(&proc_subdir_lock);
                if (!dir_emit(ctx, de->name, de->namelen,
                            de->low_ino, de->mode >> 12)) {
                        pde_put(de);
                        return 0;
                }
                ctx->pos++;
                read_lock(&proc_subdir_lock);
                next = pde_subdir_next(de);
                pde_put(de);
                de = next;
        } while (de);
        read_unlock(&proc_subdir_lock);
        return 1;
}

int proc_readdir(struct file *file, struct dir_context *ctx)
{
        struct inode *inode = file_inode(file);
        struct proc_fs_info *fs_info = proc_sb_info(inode->i_sb);

        if (fs_info->pidonly == PROC_PIDONLY_ON)
                return 1;

        return proc_readdir_de(file, ctx, PDE(inode));
}

/*
 * These are the generic /proc directory operations. They
 * use the in-memory "struct proc_dir_entry" tree to parse
 * the /proc directory.
 */
static const struct file_operations proc_dir_operations = {
        .llseek                 = generic_file_llseek,
        .read                   = generic_read_dir,
        .iterate_shared         = proc_readdir,
};

static int proc_net_d_revalidate(struct inode *dir, const struct qstr *name,
                                 struct dentry *dentry, unsigned int flags)
{
        return 0;
}

const struct dentry_operations proc_net_dentry_ops = {
        .d_revalidate   = proc_net_d_revalidate,
        .d_delete       = always_delete_dentry,
};

/*
 * proc directories can do almost nothing..
 */
static const struct inode_operations proc_dir_inode_operations = {
        .lookup         = proc_lookup,
        .getattr        = proc_getattr,
        .setattr        = proc_notify_change,
};

static void pde_set_flags(struct proc_dir_entry *pde)
{
        const struct proc_ops *proc_ops = pde->proc_ops;

        if (!proc_ops)
                return;

        if (proc_ops->proc_flags & PROC_ENTRY_PERMANENT)
                pde->flags |= PROC_ENTRY_PERMANENT;
        if (proc_ops->proc_read_iter)
                pde->flags |= PROC_ENTRY_proc_read_iter;
#ifdef CONFIG_COMPAT
        if (proc_ops->proc_compat_ioctl)
                pde->flags |= PROC_ENTRY_proc_compat_ioctl;
#endif
        if (proc_ops->proc_lseek)
                pde->flags |= PROC_ENTRY_proc_lseek;
}

/* returns the registered entry, or frees dp and returns NULL on failure */
struct proc_dir_entry *proc_register(struct proc_dir_entry *dir,
                struct proc_dir_entry *dp)
{
        if (proc_alloc_inum(&dp->low_ino))
                goto out_free_entry;

        if (!S_ISDIR(dp->mode))
                pde_set_flags(dp);

        write_lock(&proc_subdir_lock);
        dp->parent = dir;
        if (pde_subdir_insert(dir, dp) == false) {
                WARN(1, "proc_dir_entry '%s/%s' already registered\n",
                     dir->name, dp->name);
                write_unlock(&proc_subdir_lock);
                goto out_free_inum;
        }
        dir->nlink++;
        write_unlock(&proc_subdir_lock);

        return dp;
out_free_inum:
        proc_free_inum(dp->low_ino);
out_free_entry:
        pde_free(dp);
        return NULL;
}

static struct proc_dir_entry *__proc_create(struct proc_dir_entry **parent,
                                          const char *name,
                                          umode_t mode,
                                          nlink_t nlink)
{
        struct proc_dir_entry *ent = NULL;
        const char *fn;
        struct qstr qstr;

        if (xlate_proc_name(name, parent, &fn) != 0)
                goto out;
        qstr.name = fn;
        qstr.len = strlen(fn);
        if (qstr.len == 0 || qstr.len >= 256) {
                WARN(1, "name len %u\n", qstr.len);
                return NULL;
        }
        if (qstr.len == 1 && fn[0] == '.') {
                WARN(1, "name '.'\n");
                return NULL;
        }
        if (qstr.len == 2 && fn[0] == '.' && fn[1] == '.') {
                WARN(1, "name '..'\n");
                return NULL;
        }
        if (*parent == &proc_root && name_to_int(&qstr) != ~0U) {
                WARN(1, "create '/proc/%s' by hand\n", qstr.name);
                return NULL;
        }
        if (is_empty_pde(*parent)) {
                WARN(1, "attempt to add to permanently empty directory");
                return NULL;
        }

        ent = kmem_cache_zalloc(proc_dir_entry_cache, GFP_KERNEL);
        if (!ent)
                goto out;

        if (qstr.len + 1 <= SIZEOF_PDE_INLINE_NAME) {
                ent->name = ent->inline_name;
        } else {
                ent->name = kmalloc(qstr.len + 1, GFP_KERNEL);
                if (!ent->name) {
                        pde_free(ent);
                        return NULL;
                }
        }

        memcpy(ent->name, fn, qstr.len + 1);
        ent->namelen = qstr.len;
        ent->mode = mode;
        ent->nlink = nlink;
        ent->subdir = RB_ROOT;
        refcount_set(&ent->refcnt, 1);
        spin_lock_init(&ent->pde_unload_lock);
        INIT_LIST_HEAD(&ent->pde_openers);
        proc_set_user(ent, (*parent)->uid, (*parent)->gid);

        /* Revalidate everything under /proc/${pid}/net */
        if ((*parent)->flags & PROC_ENTRY_FORCE_LOOKUP)
                pde_force_lookup(ent);

out:
        return ent;
}

struct proc_dir_entry *proc_symlink(const char *name,
                struct proc_dir_entry *parent, const char *dest)
{
        struct proc_dir_entry *ent;

        ent = __proc_create(&parent, name,
                          (S_IFLNK | S_IRUGO | S_IWUGO | S_IXUGO),1);

        if (ent) {
                ent->size = strlen(dest);
                ent->data = kmemdup(dest, ent->size + 1, GFP_KERNEL);
                if (ent->data) {
                        ent->proc_iops = &proc_link_inode_operations;
                        ent = proc_register(parent, ent);
                } else {
                        pde_free(ent);
                        ent = NULL;
                }
        }
        return ent;
}
EXPORT_SYMBOL(proc_symlink);

struct proc_dir_entry *_proc_mkdir(const char *name, umode_t mode,
                struct proc_dir_entry *parent, void *data, bool force_lookup)
{
        struct proc_dir_entry *ent;

        if (mode == 0)
                mode = S_IRUGO | S_IXUGO;

        ent = __proc_create(&parent, name, S_IFDIR | mode, 2);
        if (ent) {
                ent->data = data;
                ent->proc_dir_ops = &proc_dir_operations;
                ent->proc_iops = &proc_dir_inode_operations;
                if (force_lookup) {
                        pde_force_lookup(ent);
                }
                ent = proc_register(parent, ent);
        }
        return ent;
}
EXPORT_SYMBOL_GPL(_proc_mkdir);

struct proc_dir_entry *proc_mkdir_data(const char *name, umode_t mode,
                struct proc_dir_entry *parent, void *data)
{
        return _proc_mkdir(name, mode, parent, data, false);
}
EXPORT_SYMBOL_GPL(proc_mkdir_data);

struct proc_dir_entry *proc_mkdir_mode(const char *name, umode_t mode,
                                       struct proc_dir_entry *parent)
{
        return proc_mkdir_data(name, mode, parent, NULL);
}
EXPORT_SYMBOL(proc_mkdir_mode);

struct proc_dir_entry *proc_mkdir(const char *name,
                struct proc_dir_entry *parent)
{
        return proc_mkdir_data(name, 0, parent, NULL);
}
EXPORT_SYMBOL(proc_mkdir);

struct proc_dir_entry *proc_create_mount_point(const char *name)
{
        umode_t mode = S_IFDIR | S_IRUGO | S_IXUGO;
        struct proc_dir_entry *ent, *parent = NULL;

        ent = __proc_create(&parent, name, mode, 2);
        if (ent) {
                ent->data = NULL;
                ent->proc_dir_ops = NULL;
                ent->proc_iops = NULL;
                ent = proc_register(parent, ent);
        }
        return ent;
}
EXPORT_SYMBOL(proc_create_mount_point);

struct proc_dir_entry *proc_create_reg(const char *name, umode_t mode,
                struct proc_dir_entry **parent, void *data)
{
        struct proc_dir_entry *p;

        if ((mode & S_IFMT) == 0)
                mode |= S_IFREG;
        if ((mode & S_IALLUGO) == 0)
                mode |= S_IRUGO;
        if (WARN_ON_ONCE(!S_ISREG(mode)))
                return NULL;

        p = __proc_create(parent, name, mode, 1);
        if (p) {
                p->proc_iops = &proc_file_inode_operations;
                p->data = data;
        }
        return p;
}

struct proc_dir_entry *proc_create_data(const char *name, umode_t mode,
                struct proc_dir_entry *parent,
                const struct proc_ops *proc_ops, void *data)
{
        struct proc_dir_entry *p;

        p = proc_create_reg(name, mode, &parent, data);
        if (!p)
                return NULL;
        p->proc_ops = proc_ops;
        return proc_register(parent, p);
}
EXPORT_SYMBOL(proc_create_data);
 
struct proc_dir_entry *proc_create(const char *name, umode_t mode,
                                   struct proc_dir_entry *parent,
                                   const struct proc_ops *proc_ops)
{
        return proc_create_data(name, mode, parent, proc_ops, NULL);
}
EXPORT_SYMBOL(proc_create);

static int proc_seq_open(struct inode *inode, struct file *file)
{
        struct proc_dir_entry *de = PDE(inode);

        if (de->state_size)
                return seq_open_private(file, de->seq_ops, de->state_size);
        return seq_open(file, de->seq_ops);
}

static int proc_seq_release(struct inode *inode, struct file *file)
{
        struct proc_dir_entry *de = PDE(inode);

        if (de->state_size)
                return seq_release_private(inode, file);
        return seq_release(inode, file);
}

static const struct proc_ops proc_seq_ops = {
        /* not permanent -- can call into arbitrary seq_operations */
        .proc_open      = proc_seq_open,
        .proc_read_iter = seq_read_iter,
        .proc_lseek     = seq_lseek,
        .proc_release   = proc_seq_release,
};

struct proc_dir_entry *proc_create_seq_private(const char *name, umode_t mode,
                struct proc_dir_entry *parent, const struct seq_operations *ops,
                unsigned int state_size, void *data)
{
        struct proc_dir_entry *p;

        p = proc_create_reg(name, mode, &parent, data);
        if (!p)
                return NULL;
        p->proc_ops = &proc_seq_ops;
        p->seq_ops = ops;
        p->state_size = state_size;
        return proc_register(parent, p);
}
EXPORT_SYMBOL(proc_create_seq_private);

static int proc_single_open(struct inode *inode, struct file *file)
{
        struct proc_dir_entry *de = PDE(inode);

        return single_open(file, de->single_show, de->data);
}

static const struct proc_ops proc_single_ops = {
        /* not permanent -- can call into arbitrary ->single_show */
        .proc_open      = proc_single_open,
        .proc_read_iter = seq_read_iter,
        .proc_lseek     = seq_lseek,
        .proc_release   = single_release,
};

struct proc_dir_entry *proc_create_single_data(const char *name, umode_t mode,
                struct proc_dir_entry *parent,
                int (*show)(struct seq_file *, void *), void *data)
{
        struct proc_dir_entry *p;

        p = proc_create_reg(name, mode, &parent, data);
        if (!p)
                return NULL;
        p->proc_ops = &proc_single_ops;
        p->single_show = show;
        return proc_register(parent, p);
}
EXPORT_SYMBOL(proc_create_single_data);

void proc_set_size(struct proc_dir_entry *de, loff_t size)
{
        de->size = size;
}
EXPORT_SYMBOL(proc_set_size);

void proc_set_user(struct proc_dir_entry *de, kuid_t uid, kgid_t gid)
{
        de->uid = uid;
        de->gid = gid;
}
EXPORT_SYMBOL(proc_set_user);

void pde_put(struct proc_dir_entry *pde)
{
        if (refcount_dec_and_test(&pde->refcnt)) {
                proc_free_inum(pde->low_ino);
                pde_free(pde);
        }
}

static void pde_erase(struct proc_dir_entry *pde, struct proc_dir_entry *parent)
{
        rb_erase(&pde->subdir_node, &parent->subdir);
        RB_CLEAR_NODE(&pde->subdir_node);
}

/*
 * Remove a /proc entry and free it if it's not currently in use.
 */
void remove_proc_entry(const char *name, struct proc_dir_entry *parent)
{
        struct proc_dir_entry *de = NULL;
        const char *fn = name;
        unsigned int len;

        write_lock(&proc_subdir_lock);
        if (__xlate_proc_name(name, &parent, &fn) != 0) {
                write_unlock(&proc_subdir_lock);
                return;
        }
        len = strlen(fn);

        de = pde_subdir_find(parent, fn, len);
        if (de) {
                if (unlikely(pde_is_permanent(de))) {
                        WARN(1, "removing permanent /proc entry '%s'", de->name);
                        de = NULL;
                } else {
                        pde_erase(de, parent);
                        if (S_ISDIR(de->mode))
                                parent->nlink--;
                }
        }
        write_unlock(&proc_subdir_lock);
        if (!de) {
                WARN(1, "name '%s'\n", name);
                return;
        }

        proc_entry_rundown(de);

        WARN(pde_subdir_first(de),
             "%s: removing non-empty directory '%s/%s', leaking at least '%s'\n",
             __func__, de->parent->name, de->name, pde_subdir_first(de)->name);
        pde_put(de);
}
EXPORT_SYMBOL(remove_proc_entry);

int remove_proc_subtree(const char *name, struct proc_dir_entry *parent)
{
        struct proc_dir_entry *root = NULL, *de, *next;
        const char *fn = name;
        unsigned int len;

        write_lock(&proc_subdir_lock);
        if (__xlate_proc_name(name, &parent, &fn) != 0) {
                write_unlock(&proc_subdir_lock);
                return -ENOENT;
        }
        len = strlen(fn);

        root = pde_subdir_find(parent, fn, len);
        if (!root) {
                write_unlock(&proc_subdir_lock);
                return -ENOENT;
        }
        if (unlikely(pde_is_permanent(root))) {
                write_unlock(&proc_subdir_lock);
                WARN(1, "removing permanent /proc entry '%s/%s'",
                        root->parent->name, root->name);
                return -EINVAL;
        }
        pde_erase(root, parent);

        de = root;
        while (1) {
                next = pde_subdir_first(de);
                if (next) {
                        if (unlikely(pde_is_permanent(next))) {
                                write_unlock(&proc_subdir_lock);
                                WARN(1, "removing permanent /proc entry '%s/%s'",
                                        next->parent->name, next->name);
                                return -EINVAL;
                        }
                        pde_erase(next, de);
                        de = next;
                        continue;
                }
                next = de->parent;
                if (S_ISDIR(de->mode))
                        next->nlink--;
                write_unlock(&proc_subdir_lock);

                proc_entry_rundown(de);
                if (de == root)
                        break;
                pde_put(de);

                write_lock(&proc_subdir_lock);
                de = next;
        }
        pde_put(root);
        return 0;
}
EXPORT_SYMBOL(remove_proc_subtree);

void *proc_get_parent_data(const struct inode *inode)
{
        struct proc_dir_entry *de = PDE(inode);
        return de->parent->data;
}
EXPORT_SYMBOL_GPL(proc_get_parent_data);

void proc_remove(struct proc_dir_entry *de)
{
        if (de)
                remove_proc_subtree(de->name, de->parent);
}
EXPORT_SYMBOL(proc_remove);

/*
 * Pull a user buffer into memory and pass it to the file's write handler if
 * one is supplied.  The ->write() method is permitted to modify the
 * kernel-side buffer.
 */
ssize_t proc_simple_write(struct file *f, const char __user *ubuf, size_t size,
                          loff_t *_pos)
{
        struct proc_dir_entry *pde = PDE(file_inode(f));
        char *buf;
        int ret;

        if (!pde->write)
                return -EACCES;
        if (size == 0 || size > PAGE_SIZE - 1)
                return -EINVAL;
        buf = memdup_user_nul(ubuf, size);
        if (IS_ERR(buf))
                return PTR_ERR(buf);
        ret = pde->write(f, buf, size);
        kfree(buf);
        return ret == 0 ? size : ret;
}