// SPDX-License-Identifier: GPL-2.0-only
/*
 *  Copyright (C) 2007
 *
 *  Author: Eric Biederman <ebiederm@xmision.com>
 */

#include <linux/export.h>
#include <linux/uts.h>
#include <linux/utsname.h>
#include <linux/random.h>
#include <linux/sysctl.h>
#include <linux/wait.h>
#include <linux/rwsem.h>

#ifdef CONFIG_PROC_SYSCTL

static void *get_uts(const struct ctl_table *table)
{
        char *which = table->data;
        struct uts_namespace *uts_ns;

        uts_ns = current->nsproxy->uts_ns;
        which = (which - (char *)&init_uts_ns) + (char *)uts_ns;

        return which;
}

/*
 *      Special case of dostring for the UTS structure. This has locks
 *      to observe. Should this be in kernel/sys.c ????
 */
static int proc_do_uts_string(const struct ctl_table *table, int write,
                  void *buffer, size_t *lenp, loff_t *ppos)
{
        struct ctl_table uts_table;
        int r;
        char tmp_data[__NEW_UTS_LEN + 1];

        memcpy(&uts_table, table, sizeof(uts_table));
        uts_table.data = tmp_data;

        /*
         * Buffer the value in tmp_data so that proc_dostring() can be called
         * without holding any locks.
         * We also need to read the original value in the write==1 case to
         * support partial writes.
         */
        down_read(&uts_sem);
        memcpy(tmp_data, get_uts(table), sizeof(tmp_data));
        up_read(&uts_sem);
        r = proc_dostring(&uts_table, write, buffer, lenp, ppos);

        if (write) {
                /*
                 * Write back the new value.
                 * Note that, since we dropped uts_sem, the result can
                 * theoretically be incorrect if there are two parallel writes
                 * at non-zero offsets to the same sysctl.
                 */
                add_device_randomness(tmp_data, sizeof(tmp_data));
                down_write(&uts_sem);
                memcpy(get_uts(table), tmp_data, sizeof(tmp_data));
                up_write(&uts_sem);
                proc_sys_poll_notify(table->poll);
        }

        return r;
}
#else
#define proc_do_uts_string NULL
#endif

static DEFINE_CTL_TABLE_POLL(hostname_poll);
static DEFINE_CTL_TABLE_POLL(domainname_poll);

// Note: update 'enum uts_proc' to match any changes to this table
static const struct ctl_table uts_kern_table[] = {
        {
                .procname       = "arch",
                .data           = init_uts_ns.name.machine,
                .maxlen         = sizeof(init_uts_ns.name.machine),
                .mode           = 0444,
                .proc_handler   = proc_do_uts_string,
        },
        {
                .procname       = "ostype",
                .data           = init_uts_ns.name.sysname,
                .maxlen         = sizeof(init_uts_ns.name.sysname),
                .mode           = 0444,
                .proc_handler   = proc_do_uts_string,
        },
        {
                .procname       = "osrelease",
                .data           = init_uts_ns.name.release,
                .maxlen         = sizeof(init_uts_ns.name.release),
                .mode           = 0444,
                .proc_handler   = proc_do_uts_string,
        },
        {
                .procname       = "version",
                .data           = init_uts_ns.name.version,
                .maxlen         = sizeof(init_uts_ns.name.version),
                .mode           = 0444,
                .proc_handler   = proc_do_uts_string,
        },
        {
                .procname       = "hostname",
                .data           = init_uts_ns.name.nodename,
                .maxlen         = sizeof(init_uts_ns.name.nodename),
                .mode           = 0644,
                .proc_handler   = proc_do_uts_string,
                .poll           = &hostname_poll,
        },
        {
                .procname       = "domainname",
                .data           = init_uts_ns.name.domainname,
                .maxlen         = sizeof(init_uts_ns.name.domainname),
                .mode           = 0644,
                .proc_handler   = proc_do_uts_string,
                .poll           = &domainname_poll,
        },
};

#ifdef CONFIG_PROC_SYSCTL
/*
 * Notify userspace about a change in a certain entry of uts_kern_table,
 * identified by the parameter proc.
 */
void uts_proc_notify(enum uts_proc proc)
{
        const struct ctl_table *table = &uts_kern_table[proc];

        proc_sys_poll_notify(table->poll);
}
#endif

static int __init utsname_sysctl_init(void)
{
        register_sysctl("kernel", uts_kern_table);
        return 0;
}

device_initcall(utsname_sysctl_init);