security/min_addr.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 #include <linux/init.h>
   3 #include <linux/mm.h>
   4 #include <linux/security.h>
   5 #include <linux/sysctl.h>
   6
   7 /* amount of vm to protect from userspace access by both DAC and the LSM*/
   8 unsigned long mmap_min_addr;
   9 /* amount of vm to protect from userspace using CAP_SYS_RAWIO (DAC) */
  10 unsigned long dac_mmap_min_addr = CONFIG_DEFAULT_MMAP_MIN_ADDR;
  11 /* amount of vm to protect from userspace using the LSM = CONFIG_LSM_MMAP_MIN_ADDR */
  12
  13 /*
  14  * Update mmap_min_addr = max(dac_mmap_min_addr, CONFIG_LSM_MMAP_MIN_ADDR)
  15  */
  16 static void update_mmap_min_addr(void)
  17 {
  18 #ifdef CONFIG_LSM_MMAP_MIN_ADDR
  19         if (dac_mmap_min_addr > CONFIG_LSM_MMAP_MIN_ADDR)
  20                 mmap_min_addr = dac_mmap_min_addr;
  21         else
  22                 mmap_min_addr = CONFIG_LSM_MMAP_MIN_ADDR;
  23 #else
  24         mmap_min_addr = dac_mmap_min_addr;
  25 #endif
  26 }
  27
  28 /*
  29  * sysctl handler which just sets dac_mmap_min_addr = the new value and then
  30  * calls update_mmap_min_addr() so non MAP_FIXED hints get rounded properly
  31  */
  32 int mmap_min_addr_handler(struct ctl_table *table, int write,
  33                           void *buffer, size_t *lenp, loff_t *ppos)
  34 {
  35         int ret;
  36
  37         if (write && !capable(CAP_SYS_RAWIO))
  38                 return -EPERM;
  39
  40         ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
  41
  42         update_mmap_min_addr();
  43
  44         return ret;
  45 }
  46
  47 static int __init init_mmap_min_addr(void)
  48 {
  49         update_mmap_min_addr();
  50
  51         return 0;
  52 }
  53 pure_initcall(init_mmap_min_addr);