min_addr.c

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#include <linux/init.h>
#include <linux/mm.h>
#include <linux/security.h>
#include <linux/sysctl.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
    if (dac_mmap_min_addr > CONFIG_LSM_MMAP_MIN_ADDR)
        mmap_min_addr = dac_mmap_min_addr;
    else
        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(struct ctl_table *table, int write,
              void __user *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 int __init init_mmap_min_addr(void)
{
    update_mmap_min_addr();

    return 0;
}
pure_initcall(init_mmap_min_addr);