// SPDX-License-Identifier: GPL-2.0
#include <linux/init.h>
#include <linux/mm.h>
#include <linux/security.h>
#include <linux/sysctl.h>
#include <linux/minmax.h>

/* amount of vm to protect from userspace access by both DAC and the LSM*/
unsigned long mmap_min_addr;
/* amount of vm to protect from userspace using CAP_SYS_RAWIO (DAC) */
unsigned long dac_mmap_min_addr = CONFIG_DEFAULT_MMAP_MIN_ADDR;
/* amount of vm to protect from userspace using the LSM = CONFIG_LSM_MMAP_MIN_ADDR */

/*
 * Update mmap_min_addr = max(dac_mmap_min_addr, CONFIG_LSM_MMAP_MIN_ADDR)
 */
static void update_mmap_min_addr(void)
{
#ifdef CONFIG_LSM_MMAP_MIN_ADDR
        mmap_min_addr = umax(dac_mmap_min_addr, CONFIG_LSM_MMAP_MIN_ADDR);
#else
        mmap_min_addr = dac_mmap_min_addr;
#endif
}

/*
 * sysctl handler which just sets dac_mmap_min_addr = the new value and then
 * calls update_mmap_min_addr() so non MAP_FIXED hints get rounded properly
 */
int mmap_min_addr_handler(const struct ctl_table *table, int write,
                          void *buffer, size_t *lenp, loff_t *ppos)
{
        int ret;

        if (write && !capable(CAP_SYS_RAWIO))
                return -EPERM;

        ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);

        update_mmap_min_addr();

        return ret;
}

static const struct ctl_table min_addr_sysctl_table[] = {
        {
                .procname       = "mmap_min_addr",
                .data           = &dac_mmap_min_addr,
                .maxlen         = sizeof(unsigned long),
                .mode           = 0644,
                .proc_handler   = mmap_min_addr_handler,
        },
};

static int __init mmap_min_addr_init(void)
{
        register_sysctl_init("vm", min_addr_sysctl_table);
        update_mmap_min_addr();

        return 0;
}
pure_initcall(mmap_min_addr_init);