/*
 * security/tomoyo/domain.c
 *
 * Copyright (C) 2005-2011  NTT DATA CORPORATION
 */

#include "common.h"
#include <linux/binfmts.h>
#include <linux/slab.h>

/* Variables definitions.*/

/* The initial domain. */
struct tomoyo_domain_info tomoyo_kernel_domain;

/**
 * tomoyo_update_policy - Update an entry for exception policy.
 *
 * @new_entry:       Pointer to "struct tomoyo_acl_info".
 * @size:            Size of @new_entry in bytes.
 * @param:           Pointer to "struct tomoyo_acl_param".
 * @check_duplicate: Callback function to find duplicated entry.
 *
 * Returns 0 on success, negative value otherwise.
 *
 * Caller holds tomoyo_read_lock().
 */
int tomoyo_update_policy(struct tomoyo_acl_head *new_entry, const int size,
                         struct tomoyo_acl_param *param,
                         bool (*check_duplicate) (const struct tomoyo_acl_head
                                                  *,
                                                  const struct tomoyo_acl_head
                                                  *))
{
        int error = param->is_delete ? -ENOENT : -ENOMEM;
        struct tomoyo_acl_head *entry;
        struct list_head *list = param->list;

        if (mutex_lock_interruptible(&tomoyo_policy_lock))
                return -ENOMEM;
        list_for_each_entry_rcu(entry, list, list) {
                if (!check_duplicate(entry, new_entry))
                        continue;
                entry->is_deleted = param->is_delete;
                error = 0;
                break;
        }
        if (error && !param->is_delete) {
                entry = tomoyo_commit_ok(new_entry, size);
                if (entry) {
                        list_add_tail_rcu(&entry->list, list);
                        error = 0;
                }
        }
        mutex_unlock(&tomoyo_policy_lock);
        return error;
}

/**
 * tomoyo_same_acl_head - Check for duplicated "struct tomoyo_acl_info" entry.
 *
 * @a: Pointer to "struct tomoyo_acl_info".
 * @b: Pointer to "struct tomoyo_acl_info".
 *
 * Returns true if @a == @b, false otherwise.
 */
static inline bool tomoyo_same_acl_head(const struct tomoyo_acl_info *a,
                                        const struct tomoyo_acl_info *b)
{
        return a->type == b->type && a->cond == b->cond;
}

/**
 * tomoyo_update_domain - Update an entry for domain policy.
 *
 * @new_entry:       Pointer to "struct tomoyo_acl_info".
 * @size:            Size of @new_entry in bytes.
 * @param:           Pointer to "struct tomoyo_acl_param".
 * @check_duplicate: Callback function to find duplicated entry.
 * @merge_duplicate: Callback function to merge duplicated entry.
 *
 * Returns 0 on success, negative value otherwise.
 *
 * Caller holds tomoyo_read_lock().
 */
int tomoyo_update_domain(struct tomoyo_acl_info *new_entry, const int size,
                         struct tomoyo_acl_param *param,
                         bool (*check_duplicate) (const struct tomoyo_acl_info
                                                  *,
                                                  const struct tomoyo_acl_info
                                                  *),
                         bool (*merge_duplicate) (struct tomoyo_acl_info *,
                                                  struct tomoyo_acl_info *,
                                                  const bool))
{
        const bool is_delete = param->is_delete;
        int error = is_delete ? -ENOENT : -ENOMEM;
        struct tomoyo_acl_info *entry;
        struct list_head * const list = param->list;

        if (param->data[0]) {
                new_entry->cond = tomoyo_get_condition(param);
                if (!new_entry->cond)
                        return -EINVAL;
        }
        if (mutex_lock_interruptible(&tomoyo_policy_lock))
                goto out;
        list_for_each_entry_rcu(entry, list, list) {
                if (!tomoyo_same_acl_head(entry, new_entry) ||
                    !check_duplicate(entry, new_entry))
                        continue;
                if (merge_duplicate)
                        entry->is_deleted = merge_duplicate(entry, new_entry,
                                                            is_delete);
                else
                        entry->is_deleted = is_delete;
                error = 0;
                break;
        }
        if (error && !is_delete) {
                entry = tomoyo_commit_ok(new_entry, size);
                if (entry) {
                        list_add_tail_rcu(&entry->list, list);
                        error = 0;
                }
        }
        mutex_unlock(&tomoyo_policy_lock);
out:
        tomoyo_put_condition(new_entry->cond);
        return error;
}

/**
 * tomoyo_check_acl - Do permission check.
 *
 * @r:           Pointer to "struct tomoyo_request_info".
 * @check_entry: Callback function to check type specific parameters.
 *
 * Returns 0 on success, negative value otherwise.
 *
 * Caller holds tomoyo_read_lock().
 */
void tomoyo_check_acl(struct tomoyo_request_info *r,
                      bool (*check_entry) (struct tomoyo_request_info *,
                                           const struct tomoyo_acl_info *))
{
        const struct tomoyo_domain_info *domain = r->domain;
        struct tomoyo_acl_info *ptr;
        bool retried = false;
        const struct list_head *list = &domain->acl_info_list;

retry:
        list_for_each_entry_rcu(ptr, list, list) {
                if (ptr->is_deleted || ptr->type != r->param_type)
                        continue;
                if (!check_entry(r, ptr))
                        continue;
                if (!tomoyo_condition(r, ptr->cond))
                        continue;
                r->granted = true;
                return;
        }
        if (!retried) {
                retried = true;
                list = &domain->ns->acl_group[domain->group];
                goto retry;
        }
        r->granted = false;
}

/* The list for "struct tomoyo_domain_info". */
LIST_HEAD(tomoyo_domain_list);

/**
 * tomoyo_last_word - Get last component of a domainname.
 *
 * @name: Domainname to check.
 *
 * Returns the last word of @domainname.
 */
static const char *tomoyo_last_word(const char *name)
{
        const char *cp = strrchr(name, ' ');
        if (cp)
                return cp + 1;
        return name;
}

/**
 * tomoyo_same_transition_control - Check for duplicated "struct tomoyo_transition_control" entry.
 *
 * @a: Pointer to "struct tomoyo_acl_head".
 * @b: Pointer to "struct tomoyo_acl_head".
 *
 * Returns true if @a == @b, false otherwise.
 */
static bool tomoyo_same_transition_control(const struct tomoyo_acl_head *a,
                                           const struct tomoyo_acl_head *b)
{
        const struct tomoyo_transition_control *p1 = container_of(a,
                                                                  typeof(*p1),
                                                                  head);
        const struct tomoyo_transition_control *p2 = container_of(b,
                                                                  typeof(*p2),
                                                                  head);
        return p1->type == p2->type && p1->is_last_name == p2->is_last_name
                && p1->domainname == p2->domainname
                && p1->program == p2->program;
}

/**
 * tomoyo_write_transition_control - Write "struct tomoyo_transition_control" list.
 *
 * @param: Pointer to "struct tomoyo_acl_param".
 * @type:  Type of this entry.
 *
 * Returns 0 on success, negative value otherwise.
 */
int tomoyo_write_transition_control(struct tomoyo_acl_param *param,
                                    const u8 type)
{
        struct tomoyo_transition_control e = { .type = type };
        int error = param->is_delete ? -ENOENT : -ENOMEM;
        char *program = param->data;
        char *domainname = strstr(program, " from ");
        if (domainname) {
                *domainname = '\0';
                domainname += 6;
        } else if (type == TOMOYO_TRANSITION_CONTROL_NO_KEEP ||
                   type == TOMOYO_TRANSITION_CONTROL_KEEP) {
                domainname = program;
                program = NULL;
        }
        if (program && strcmp(program, "any")) {
                if (!tomoyo_correct_path(program))
                        return -EINVAL;
                e.program = tomoyo_get_name(program);
                if (!e.program)
                        goto out;
        }
        if (domainname && strcmp(domainname, "any")) {
                if (!tomoyo_correct_domain(domainname)) {
                        if (!tomoyo_correct_path(domainname))
                                goto out;
                        e.is_last_name = true;
                }
                e.domainname = tomoyo_get_name(domainname);
                if (!e.domainname)
                        goto out;
        }
        param->list = &param->ns->policy_list[TOMOYO_ID_TRANSITION_CONTROL];
        error = tomoyo_update_policy(&e.head, sizeof(e), param,
                                     tomoyo_same_transition_control);
out:
        tomoyo_put_name(e.domainname);
        tomoyo_put_name(e.program);
        return error;
}

/**
 * tomoyo_scan_transition - Try to find specific domain transition type.
 *
 * @list:       Pointer to "struct list_head".
 * @domainname: The name of current domain.
 * @program:    The name of requested program.
 * @last_name:  The last component of @domainname.
 * @type:       One of values in "enum tomoyo_transition_type".
 *
 * Returns true if found one, false otherwise.
 *
 * Caller holds tomoyo_read_lock().
 */
static inline bool tomoyo_scan_transition
(const struct list_head *list, const struct tomoyo_path_info *domainname,
 const struct tomoyo_path_info *program, const char *last_name,
 const enum tomoyo_transition_type type)
{
        const struct tomoyo_transition_control *ptr;
        list_for_each_entry_rcu(ptr, list, head.list) {
                if (ptr->head.is_deleted || ptr->type != type)
                        continue;
                if (ptr->domainname) {
                        if (!ptr->is_last_name) {
                                if (ptr->domainname != domainname)
                                        continue;
                        } else {
                                /*
                                 * Use direct strcmp() since this is
                                 * unlikely used.
                                 */
                                if (strcmp(ptr->domainname->name, last_name))
                                        continue;
                        }
                }
                if (ptr->program && tomoyo_pathcmp(ptr->program, program))
                        continue;
                return true;
        }
        return false;
}

/**
 * tomoyo_transition_type - Get domain transition type.
 *
 * @ns:         Pointer to "struct tomoyo_policy_namespace".
 * @domainname: The name of current domain.
 * @program:    The name of requested program.
 *
 * Returns TOMOYO_TRANSITION_CONTROL_TRANSIT if executing @program causes
 * domain transition across namespaces, TOMOYO_TRANSITION_CONTROL_INITIALIZE if
 * executing @program reinitializes domain transition within that namespace,
 * TOMOYO_TRANSITION_CONTROL_KEEP if executing @program stays at @domainname ,
 * others otherwise.
 *
 * Caller holds tomoyo_read_lock().
 */
static enum tomoyo_transition_type tomoyo_transition_type
(const struct tomoyo_policy_namespace *ns,
 const struct tomoyo_path_info *domainname,
 const struct tomoyo_path_info *program)
{
        const char *last_name = tomoyo_last_word(domainname->name);
        enum tomoyo_transition_type type = TOMOYO_TRANSITION_CONTROL_NO_RESET;
        while (type < TOMOYO_MAX_TRANSITION_TYPE) {
                const struct list_head * const list =
                        &ns->policy_list[TOMOYO_ID_TRANSITION_CONTROL];
                if (!tomoyo_scan_transition(list, domainname, program,
                                            last_name, type)) {
                        type++;
                        continue;
                }
                if (type != TOMOYO_TRANSITION_CONTROL_NO_RESET &&
                    type != TOMOYO_TRANSITION_CONTROL_NO_INITIALIZE)
                        break;
                /*
                 * Do not check for reset_domain if no_reset_domain matched.
                 * Do not check for initialize_domain if no_initialize_domain
                 * matched.
                 */
                type++;
                type++;
        }
        return type;
}

/**
 * tomoyo_same_aggregator - Check for duplicated "struct tomoyo_aggregator" entry.
 *
 * @a: Pointer to "struct tomoyo_acl_head".
 * @b: Pointer to "struct tomoyo_acl_head".
 *
 * Returns true if @a == @b, false otherwise.
 */
static bool tomoyo_same_aggregator(const struct tomoyo_acl_head *a,
                                   const struct tomoyo_acl_head *b)
{
        const struct tomoyo_aggregator *p1 = container_of(a, typeof(*p1),
                                                          head);
        const struct tomoyo_aggregator *p2 = container_of(b, typeof(*p2),
                                                          head);
        return p1->original_name == p2->original_name &&
                p1->aggregated_name == p2->aggregated_name;
}

/**
 * tomoyo_write_aggregator - Write "struct tomoyo_aggregator" list.
 *
 * @param: Pointer to "struct tomoyo_acl_param".
 *
 * Returns 0 on success, negative value otherwise.
 *
 * Caller holds tomoyo_read_lock().
 */
int tomoyo_write_aggregator(struct tomoyo_acl_param *param)
{
        struct tomoyo_aggregator e = { };
        int error = param->is_delete ? -ENOENT : -ENOMEM;
        const char *original_name = tomoyo_read_token(param);
        const char *aggregated_name = tomoyo_read_token(param);
        if (!tomoyo_correct_word(original_name) ||
            !tomoyo_correct_path(aggregated_name))
                return -EINVAL;
        e.original_name = tomoyo_get_name(original_name);
        e.aggregated_name = tomoyo_get_name(aggregated_name);
        if (!e.original_name || !e.aggregated_name ||
            e.aggregated_name->is_patterned) /* No patterns allowed. */
                goto out;
        param->list = &param->ns->policy_list[TOMOYO_ID_AGGREGATOR];
        error = tomoyo_update_policy(&e.head, sizeof(e), param,
                                     tomoyo_same_aggregator);
out:
        tomoyo_put_name(e.original_name);
        tomoyo_put_name(e.aggregated_name);
        return error;
}

/**
 * tomoyo_find_namespace - Find specified namespace.
 *
 * @name: Name of namespace to find.
 * @len:  Length of @name.
 *
 * Returns pointer to "struct tomoyo_policy_namespace" if found,
 * NULL otherwise.
 *
 * Caller holds tomoyo_read_lock().
 */
static struct tomoyo_policy_namespace *tomoyo_find_namespace
(const char *name, const unsigned int len)
{
        struct tomoyo_policy_namespace *ns;
        list_for_each_entry(ns, &tomoyo_namespace_list, namespace_list) {
                if (strncmp(name, ns->name, len) ||
                    (name[len] && name[len] != ' '))
                        continue;
                return ns;
        }
        return NULL;
}

/**
 * tomoyo_assign_namespace - Create a new namespace.
 *
 * @domainname: Name of namespace to create.
 *
 * Returns pointer to "struct tomoyo_policy_namespace" on success,
 * NULL otherwise.
 *
 * Caller holds tomoyo_read_lock().
 */
struct tomoyo_policy_namespace *tomoyo_assign_namespace(const char *domainname)
{
        struct tomoyo_policy_namespace *ptr;
        struct tomoyo_policy_namespace *entry;
        const char *cp = domainname;
        unsigned int len = 0;
        while (*cp && *cp++ != ' ')
                len++;
        ptr = tomoyo_find_namespace(domainname, len);
        if (ptr)
                return ptr;
        if (len >= TOMOYO_EXEC_TMPSIZE - 10 || !tomoyo_domain_def(domainname))
                return NULL;
        entry = kzalloc(sizeof(*entry) + len + 1, GFP_NOFS);
        if (!entry)
                return NULL;
        if (mutex_lock_interruptible(&tomoyo_policy_lock))
                goto out;
        ptr = tomoyo_find_namespace(domainname, len);
        if (!ptr && tomoyo_memory_ok(entry)) {
                char *name = (char *) (entry + 1);
                ptr = entry;
                memmove(name, domainname, len);
                name[len] = '\0';
                entry->name = name;
                tomoyo_init_policy_namespace(entry);
                entry = NULL;
        }
        mutex_unlock(&tomoyo_policy_lock);
out:
        kfree(entry);
        return ptr;
}

/**
 * tomoyo_namespace_jump - Check for namespace jump.
 *
 * @domainname: Name of domain.
 *
 * Returns true if namespace differs, false otherwise.
 */
static bool tomoyo_namespace_jump(const char *domainname)
{
        const char *namespace = tomoyo_current_namespace()->name;
        const int len = strlen(namespace);
        return strncmp(domainname, namespace, len) ||
                (domainname[len] && domainname[len] != ' ');
}

/**
 * tomoyo_assign_domain - Create a domain or a namespace.
 *
 * @domainname: The name of domain.
 * @transit:    True if transit to domain found or created.
 *
 * Returns pointer to "struct tomoyo_domain_info" on success, NULL otherwise.
 *
 * Caller holds tomoyo_read_lock().
 */
struct tomoyo_domain_info *tomoyo_assign_domain(const char *domainname,
                                                const bool transit)
{
        struct tomoyo_domain_info e = { };
        struct tomoyo_domain_info *entry = tomoyo_find_domain(domainname);
        bool created = false;
        if (entry) {
                if (transit) {
                        /*
                         * Since namespace is created at runtime, profiles may
                         * not be created by the moment the process transits to
                         * that domain. Do not perform domain transition if
                         * profile for that domain is not yet created.
                         */
                        if (!entry->ns->profile_ptr[entry->profile])
                                return NULL;
                }
                return entry;
        }
        /* Requested domain does not exist. */
        /* Don't create requested domain if domainname is invalid. */
        if (strlen(domainname) >= TOMOYO_EXEC_TMPSIZE - 10 ||
            !tomoyo_correct_domain(domainname))
                return NULL;
        /*
         * Since definition of profiles and acl_groups may differ across
         * namespaces, do not inherit "use_profile" and "use_group" settings
         * by automatically creating requested domain upon domain transition.
         */
        if (transit && tomoyo_namespace_jump(domainname))
                return NULL;
        e.ns = tomoyo_assign_namespace(domainname);
        if (!e.ns)
                return NULL;
        /*
         * "use_profile" and "use_group" settings for automatically created
         * domains are inherited from current domain. These are 0 for manually
         * created domains.
         */
        if (transit) {
                const struct tomoyo_domain_info *domain = tomoyo_domain();
                e.profile = domain->profile;
                e.group = domain->group;
        }
        e.domainname = tomoyo_get_name(domainname);
        if (!e.domainname)
                return NULL;
        if (mutex_lock_interruptible(&tomoyo_policy_lock))
                goto out;
        entry = tomoyo_find_domain(domainname);
        if (!entry) {
                entry = tomoyo_commit_ok(&e, sizeof(e));
                if (entry) {
                        INIT_LIST_HEAD(&entry->acl_info_list);
                        list_add_tail_rcu(&entry->list, &tomoyo_domain_list);
                        created = true;
                }
        }
        mutex_unlock(&tomoyo_policy_lock);
out:
        tomoyo_put_name(e.domainname);
        if (entry && transit) {
                if (created) {
                        struct tomoyo_request_info r;
                        tomoyo_init_request_info(&r, entry,
                                                 TOMOYO_MAC_FILE_EXECUTE);
                        r.granted = false;
                        tomoyo_write_log(&r, "use_profile %u\n",
                                         entry->profile);
                        tomoyo_write_log(&r, "use_group %u\n", entry->group);
                }
        }
        return entry;
}

/**
 * tomoyo_find_next_domain - Find a domain.
 *
 * @bprm: Pointer to "struct linux_binprm".
 *
 * Returns 0 on success, negative value otherwise.
 *
 * Caller holds tomoyo_read_lock().
 */
int tomoyo_find_next_domain(struct linux_binprm *bprm)
{
        struct tomoyo_domain_info *old_domain = tomoyo_domain();
        struct tomoyo_domain_info *domain = NULL;
        const char *original_name = bprm->filename;
        int retval = -ENOMEM;
        bool need_kfree = false;
        bool reject_on_transition_failure = false;
        struct tomoyo_path_info rn = { }; /* real name */
        struct tomoyo_execve *ee = kzalloc(sizeof(*ee), GFP_NOFS);
        if (!ee)
                return -ENOMEM;
        ee->tmp = kzalloc(TOMOYO_EXEC_TMPSIZE, GFP_NOFS);
        if (!ee->tmp) {
                kfree(ee);
                return -ENOMEM;
        }
        /* ee->dump->data is allocated by tomoyo_dump_page(). */
        tomoyo_init_request_info(&ee->r, NULL, TOMOYO_MAC_FILE_EXECUTE);
        ee->r.ee = ee;
        ee->bprm = bprm;
        ee->r.obj = &ee->obj;
        ee->obj.path1 = bprm->file->f_path;
 retry:
        if (need_kfree) {
                kfree(rn.name);
                need_kfree = false;
        }
        /* Get symlink's pathname of program. */
        retval = -ENOENT;
        rn.name = tomoyo_realpath_nofollow(original_name);
        if (!rn.name)
                goto out;
        tomoyo_fill_path_info(&rn);
        need_kfree = true;

        /* Check 'aggregator' directive. */
        {
                struct tomoyo_aggregator *ptr;
                struct list_head *list =
                        &old_domain->ns->policy_list[TOMOYO_ID_AGGREGATOR];
                /* Check 'aggregator' directive. */
                list_for_each_entry_rcu(ptr, list, head.list) {
                        if (ptr->head.is_deleted ||
                            !tomoyo_path_matches_pattern(&rn,
                                                         ptr->original_name))
                                continue;
                        kfree(rn.name);
                        need_kfree = false;
                        /* This is OK because it is read only. */
                        rn = *ptr->aggregated_name;
                        break;
                }
        }

        /* Check execute permission. */
        retval = tomoyo_path_permission(&ee->r, TOMOYO_TYPE_EXECUTE, &rn);
        if (retval == TOMOYO_RETRY_REQUEST)
                goto retry;
        if (retval < 0)
                goto out;
        /*
         * To be able to specify domainnames with wildcards, use the
         * pathname specified in the policy (which may contain
         * wildcard) rather than the pathname passed to execve()
         * (which never contains wildcard).
         */
        if (ee->r.param.path.matched_path) {
                if (need_kfree)
                        kfree(rn.name);
                need_kfree = false;
                /* This is OK because it is read only. */
                rn = *ee->r.param.path.matched_path;
        }

        /* Calculate domain to transit to. */
        switch (tomoyo_transition_type(old_domain->ns, old_domain->domainname,
                                       &rn)) {
        case TOMOYO_TRANSITION_CONTROL_RESET:
                /* Transit to the root of specified namespace. */
                snprintf(ee->tmp, TOMOYO_EXEC_TMPSIZE - 1, "<%s>", rn.name);
                /*
                 * Make do_execve() fail if domain transition across namespaces
                 * has failed.
                 */
                reject_on_transition_failure = true;
                break;
        case TOMOYO_TRANSITION_CONTROL_INITIALIZE:
                /* Transit to the child of current namespace's root. */
                snprintf(ee->tmp, TOMOYO_EXEC_TMPSIZE - 1, "%s %s",
                         old_domain->ns->name, rn.name);
                break;
        case TOMOYO_TRANSITION_CONTROL_KEEP:
                /* Keep current domain. */
                domain = old_domain;
                break;
        default:
                if (old_domain == &tomoyo_kernel_domain &&
                    !tomoyo_policy_loaded) {
                        /*
                         * Needn't to transit from kernel domain before
                         * starting /sbin/init. But transit from kernel domain
                         * if executing initializers because they might start
                         * before /sbin/init.
                         */
                        domain = old_domain;
                } else {
                        /* Normal domain transition. */
                        snprintf(ee->tmp, TOMOYO_EXEC_TMPSIZE - 1, "%s %s",
                                 old_domain->domainname->name, rn.name);
                }
                break;
        }
        if (!domain)
                domain = tomoyo_assign_domain(ee->tmp, true);
        if (domain)
                retval = 0;
        else if (reject_on_transition_failure) {
                printk(KERN_WARNING "ERROR: Domain '%s' not ready.\n",
                       ee->tmp);
                retval = -ENOMEM;
        } else if (ee->r.mode == TOMOYO_CONFIG_ENFORCING)
                retval = -ENOMEM;
        else {
                retval = 0;
                if (!old_domain->flags[TOMOYO_DIF_TRANSITION_FAILED]) {
                        old_domain->flags[TOMOYO_DIF_TRANSITION_FAILED] = true;
                        ee->r.granted = false;
                        tomoyo_write_log(&ee->r, "%s", tomoyo_dif
                                         [TOMOYO_DIF_TRANSITION_FAILED]);
                        printk(KERN_WARNING
                               "ERROR: Domain '%s' not defined.\n", ee->tmp);
                }
        }
 out:
        if (!domain)
                domain = old_domain;
        /* Update reference count on "struct tomoyo_domain_info". */
        atomic_inc(&domain->users);
        bprm->cred->security = domain;
        if (need_kfree)
                kfree(rn.name);
        kfree(ee->tmp);
        kfree(ee->dump.data);
        kfree(ee);
        return retval;
}

/**
 * tomoyo_dump_page - Dump a page to buffer.
 *
 * @bprm: Pointer to "struct linux_binprm".
 * @pos:  Location to dump.
 * @dump: Poiner to "struct tomoyo_page_dump".
 *
 * Returns true on success, false otherwise.
 */
bool tomoyo_dump_page(struct linux_binprm *bprm, unsigned long pos,
                      struct tomoyo_page_dump *dump)
{
        struct page *page;
        /* dump->data is released by tomoyo_finish_execve(). */
        if (!dump->data) {
                dump->data = kzalloc(PAGE_SIZE, GFP_NOFS);
                if (!dump->data)
                        return false;
        }
        /* Same with get_arg_page(bprm, pos, 0) in fs/exec.c */
#ifdef CONFIG_MMU
        if (get_user_pages(current, bprm->mm, pos, 1, 0, 1, &page, NULL) <= 0)
                return false;
#else
        page = bprm->page[pos / PAGE_SIZE];
#endif
        if (page != dump->page) {
                const unsigned int offset = pos % PAGE_SIZE;
                /*
                 * Maybe kmap()/kunmap() should be used here.
                 * But remove_arg_zero() uses kmap_atomic()/kunmap_atomic().
                 * So do I.
                 */
                char *kaddr = kmap_atomic(page, KM_USER0);
                dump->page = page;
                memcpy(dump->data + offset, kaddr + offset,
                       PAGE_SIZE - offset);
                kunmap_atomic(kaddr, KM_USER0);
        }
        /* Same with put_arg_page(page) in fs/exec.c */
#ifdef CONFIG_MMU
        put_page(page);
#endif
        return true;
}