security/lowmem.c

   1 #include <linux/module.h>
   2 #include <linux/kernel.h>
   3 #include <linux/mman.h>
   4 #include <linux/init.h>
   5 #include <linux/security.h>
   6 #include <linux/sysctl.h>
   7 #include <linux/swap.h>
   8 #include <linux/kobject.h>
   9 #include <linux/pagemap.h>
  10 #include <linux/hugetlb.h>
  11 #include <linux/sysfs.h>
  12 #include <linux/oom.h>
  13
  14 #define MY_NAME "lowmem"
  15
  16 #define LOWMEM_MAX_UIDS 8
  17
  18 enum {
  19         VM_LOWMEM_DENY = 1,
  20         VM_LOWMEM_LEVEL1_NOTIFY,
  21         VM_LOWMEM_LEVEL2_NOTIFY,
  22         VM_LOWMEM_NR_DECAY_PAGES,
  23         VM_LOWMEM_ALLOWED_UIDS,
  24         VM_LOWMEM_ALLOWED_PAGES,
  25         VM_LOWMEM_USED_PAGES,
  26 };
  27
  28 static unsigned int deny_percentage;
  29 static unsigned int l1_notify, l2_notify;
  30 static unsigned int nr_decay_pages;
  31 static unsigned long allowed_pages;
  32 static long used_pages;
  33 static unsigned int allowed_uids[LOWMEM_MAX_UIDS];
  34 static unsigned int minuid = 1;
  35 static unsigned int maxuid = 65535;
  36
  37 static ctl_table lowmem_table[] = {
  38         {
  39                 .ctl_name = VM_LOWMEM_DENY,
  40                 .procname = "lowmem_deny_watermark",
  41                 .data = &deny_percentage,
  42                 .maxlen = sizeof(unsigned int),
  43                 .mode = 0644,
  44                 .child = NULL,
  45                 .proc_handler = &proc_dointvec,
  46                 .strategy = &sysctl_intvec,
  47         }, {
  48                 .ctl_name = VM_LOWMEM_LEVEL1_NOTIFY,
  49                 .procname = "lowmem_notify_low",
  50                 .data = &l1_notify,
  51                 .maxlen = sizeof(unsigned int),
  52                 .mode = 0644,
  53                 .child = NULL,
  54                 .proc_handler = &proc_dointvec,
  55                 .strategy = &sysctl_intvec,
  56         }, {
  57                 .ctl_name = VM_LOWMEM_LEVEL2_NOTIFY,
  58                 .procname = "lowmem_notify_high",
  59                 .data = &l2_notify,
  60                 .maxlen = sizeof(unsigned int),
  61                 .mode = 0644,
  62                 .child = NULL,
  63                 .proc_handler = &proc_dointvec,
  64                 .strategy = &sysctl_intvec,
  65         }, {
  66                 .ctl_name = VM_LOWMEM_NR_DECAY_PAGES,
  67                 .procname = "lowmem_nr_decay_pages",
  68                 .data = &nr_decay_pages,
  69                 .maxlen = sizeof(unsigned int),
  70                 .mode = 0644,
  71                 .child = NULL,
  72                 .proc_handler = &proc_dointvec,
  73                 .strategy = &sysctl_intvec,
  74         }, {
  75                 .ctl_name = VM_LOWMEM_ALLOWED_UIDS,
  76                 .procname = "lowmem_allowed_uids",
  77                 .data = &allowed_uids,
  78                 .maxlen = LOWMEM_MAX_UIDS * sizeof(unsigned int),
  79                 .mode = 0644,
  80                 .child = NULL,
  81                 .proc_handler = &proc_dointvec_minmax,
  82                 .strategy = &sysctl_intvec,
  83                 .extra1 = &minuid,
  84                 .extra2 = &maxuid,
  85         }, {
  86                 .ctl_name = VM_LOWMEM_ALLOWED_PAGES,
  87                 .procname = "lowmem_allowed_pages",
  88                 .data = &allowed_pages,
  89                 .maxlen = sizeof(unsigned long),
  90                 .mode = 0444,
  91                 .child = NULL,
  92                 .proc_handler = &proc_dointvec,
  93                 .strategy = &sysctl_intvec,
  94         }, {
  95                 .ctl_name = VM_LOWMEM_USED_PAGES,
  96                 .procname = "lowmem_used_pages",
  97                 .data = &used_pages,
  98                 .maxlen = sizeof(long),
  99                 .mode = 0444,
 100                 .child = NULL,
 101                 .proc_handler = &proc_dointvec,
 102                 .strategy = &sysctl_intvec,
 103         }, {
 104                 .ctl_name = 0
 105         }
 106 };
 107
 108 static ctl_table lowmem_root_table[] = {
 109         {
 110                 .ctl_name = CTL_VM,
 111                 .procname = "vm",
 112                 .mode = 0555,
 113                 .child = lowmem_table,
 114         }, {
 115                 .ctl_name = 0
 116         }
 117 };
 118
 119 #define KERNEL_ATTR_RO(_name) \
 120 static struct subsys_attribute _name##_attr = __ATTR_RO(_name)
 121
 122 static int low_watermark_reached, high_watermark_reached;
 123
 124 static ssize_t low_watermark_show(struct subsystem *subsys, char *page)
 125 {
 126         return sprintf(page, "%u\n", low_watermark_reached);
 127 }
 128
 129 static ssize_t high_watermark_show(struct subsystem *subsys, char *page)
 130 {
 131         return sprintf(page, "%u\n", high_watermark_reached);
 132 }
 133
 134 KERNEL_ATTR_RO(low_watermark);
 135 KERNEL_ATTR_RO(high_watermark);
 136
 137 static void low_watermark_state(int new_state)
 138 {
 139         int changed = 0;
 140
 141         if (low_watermark_reached != new_state) {
 142                 low_watermark_reached = new_state;
 143                 changed = 1;
 144         }
 145
 146         if (changed)
 147                 sysfs_notify(&kernel_subsys.kset.kobj, NULL, "low_watermark");
 148 }
 149
 150 static void high_watermark_state(int new_state)
 151 {
 152         int changed = 0;
 153
 154         if (high_watermark_reached != new_state) {
 155                 high_watermark_reached = new_state;
 156                 changed = 1;
 157         }
 158
 159         if (changed)
 160                 sysfs_notify(&kernel_subsys.kset.kobj, NULL, "high_watermark");
 161 }
 162
 163 static int low_vm_enough_memory(long pages)
 164 {
 165         unsigned long free, allowed;
 166         long deny_threshold, level1, level2, used;
 167         int cap_sys_admin = 0, notify;
 168
 169         if (cap_capable(current, CAP_SYS_ADMIN) == 0)
 170                 cap_sys_admin = 1;
 171
 172         /* We activate ourselves only after both parameters have been
 173          * configured. */
 174         if (deny_percentage == 0 || l1_notify == 0 || l2_notify == 0)
 175                 return __vm_enough_memory(pages, cap_sys_admin);
 176
 177         allowed = totalram_pages - hugetlb_total_pages();
 178         deny_threshold = allowed * deny_percentage / 100;
 179         level1 = allowed * l1_notify / 100;
 180         level2 = allowed * l2_notify / 100;
 181
 182         vm_acct_memory(pages);
 183
 184         /* Easily freed pages when under VM pressure or direct reclaim */
 185         free = global_page_state(NR_FILE_PAGES);
 186         free += nr_swap_pages;
 187         free += global_page_state(NR_SLAB_RECLAIMABLE);
 188
 189         used = allowed - free;
 190         if (unlikely(used < 0))
 191                 used = 0;
 192
 193         /* The hot path, plenty of memory */
 194         if (likely(used < level1))
 195                 goto enough_memory;
 196
 197         /* No luck, lets make it more expensive and try again.. */
 198         used -= nr_free_pages();
 199
 200         if (used >= deny_threshold) {
 201                 int i;
 202
 203                 allowed_pages = allowed;
 204                 used_pages = used;
 205                 low_watermark_state(1);
 206                 high_watermark_state(1);
 207                 /* Memory allocations by root are always allowed */
 208                 if (cap_sys_admin)
 209                         return 0;
 210
 211                 /* OOM unkillable process is allowed to consume memory */
 212                 if (current->oomkilladj == OOM_DISABLE)
 213                         return 0;
 214
 215                 /* uids from allowed_uids vector are also allowed no matter what */
 216                 for (i = 0; i < LOWMEM_MAX_UIDS && allowed_uids[i]; i++)
 217                         if (current->uid == allowed_uids[i])
 218                                 return 0;
 219
 220                 vm_unacct_memory(pages);
 221                 if (printk_ratelimit()) {
 222                         printk(MY_NAME ": denying memory allocation to process %d (%s)\n",
 223                                current->pid, current->comm);
 224                 }
 225                 return -ENOMEM;
 226         }
 227
 228 enough_memory:
 229         /* See if we need to notify level 1 */
 230         low_watermark_state(used >= level1);
 231
 232         /*
 233          * In the level 2 notification case things are more complicated,
 234          * as the level that we drop the state and send a notification
 235          * should be lower than when it is first triggered. Having this
 236          * on the same watermark level ends up bouncing back and forth
 237          * when applications are being stupid.
 238          */
 239         notify = used >= level2;
 240         if (notify || used + nr_decay_pages < level2)
 241                 high_watermark_state(notify);
 242
 243         /* We have plenty of memory */
 244         allowed_pages = allowed;
 245         used_pages = used;
 246         return 0;
 247 }
 248
 249 static struct security_operations lowmem_security_ops = {
 250         /* Use the capability functions for some of the hooks */
 251         .ptrace = cap_ptrace,
 252         .capget = cap_capget,
 253         .capset_check = cap_capset_check,
 254         .capset_set = cap_capset_set,
 255         .capable = cap_capable,
 256
 257         .bprm_apply_creds = cap_bprm_apply_creds,
 258         .bprm_set_security = cap_bprm_set_security,
 259
 260         .task_post_setuid = cap_task_post_setuid,
 261         .task_reparent_to_init = cap_task_reparent_to_init,
 262         .vm_enough_memory = low_vm_enough_memory,
 263 };
 264
 265 static struct ctl_table_header *lowmem_table_header;
 266 /* flag to keep track of how we were registered */
 267 static int secondary;
 268
 269 static struct attribute *lowmem_attrs[] = {
 270         &low_watermark_attr.attr,
 271         &high_watermark_attr.attr,
 272         NULL,
 273 };
 274
 275 static struct attribute_group lowmem_attr_group = {
 276         .attrs  = lowmem_attrs,
 277 };
 278
 279 static int __init lowmem_init(void)
 280 {
 281         int r;
 282
 283         /* register ourselves with the security framework */
 284         if (register_security(&lowmem_security_ops)) {
 285                 printk(KERN_ERR MY_NAME ": Failure registering with the kernel\n");
 286                 /* try registering with primary module */
 287                 if (mod_reg_security(MY_NAME, &lowmem_security_ops)) {
 288                         printk(KERN_ERR ": Failure registering with the primary"
 289                                "security module.\n");
 290                         return -EINVAL;
 291                 }
 292                 secondary = 1;
 293         }
 294
 295         /* initialize the uids vector */
 296         memset(allowed_uids, 0, sizeof(allowed_uids));
 297
 298         lowmem_table_header = register_sysctl_table(lowmem_root_table);
 299         if (unlikely(!lowmem_table_header))
 300                 return -EPERM;
 301
 302         kernel_subsys.kset.kobj.kset = &kernel_subsys.kset;
 303
 304         r = sysfs_create_group(&kernel_subsys.kset.kobj,
 305                                &lowmem_attr_group);
 306         if (unlikely(r))
 307                 return r;
 308
 309         printk(KERN_INFO MY_NAME ": Module initialized.\n");
 310
 311         return 0;
 312 }
 313
 314 static void __exit lowmem_exit(void)
 315 {
 316         /* remove ourselves from the security framework */
 317         if (secondary) {
 318                 if (mod_unreg_security(MY_NAME, &lowmem_security_ops))
 319                         printk(KERN_ERR MY_NAME ": Failure unregistering "
 320                                "with the primary security module.\n");
 321         } else {
 322                 if (unregister_security(&lowmem_security_ops)) {
 323                         printk(KERN_ERR MY_NAME ": Failure unregistering "
 324                                "with the kernel.\n");
 325                 }
 326         }
 327
 328         unregister_sysctl_table(lowmem_table_header);
 329
 330         sysfs_remove_group(&kernel_subsys.kset.kobj, &lowmem_attr_group);
 331
 332         printk(KERN_INFO MY_NAME ": Module removed.\n");
 333 }
 334
 335 module_init(lowmem_init);
 336 module_exit(lowmem_exit);
 337
 338 MODULE_DESCRIPTION("Low watermark LSM module");
 339 MODULE_LICENSE("GPL");