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_PAGES = 1,
  20         VM_LOWMEM_NOTIFY_LOW_PAGES,
  21         VM_LOWMEM_NOTIFY_HIGH_PAGES,
  22         VM_LOWMEM_NR_DECAY_PAGES,
  23         VM_LOWMEM_ALLOWED_UIDS,
  24         VM_LOWMEM_ALLOWED_PAGES,
  25         VM_LOWMEM_FREE_PAGES,
  26 };
  27
  28 static long deny_pages;
  29 static long notify_low_pages, notify_high_pages;
  30 static unsigned int nr_decay_pages;
  31 static unsigned long allowed_pages;
  32 static unsigned long lowmem_free_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_PAGES,
  40                 .procname = "lowmem_deny_watermark_pages",
  41                 .data = &deny_pages,
  42                 .maxlen = sizeof(long),
  43                 .mode = 0644,
  44                 .child = NULL,
  45                 .proc_handler = &proc_dointvec,
  46                 .strategy = &sysctl_intvec,
  47         }, {
  48                 .ctl_name = VM_LOWMEM_NOTIFY_LOW_PAGES,
  49                 .procname = "lowmem_notify_low_pages",
  50                 .data = &notify_low_pages,
  51                 .maxlen = sizeof(long),
  52                 .mode = 0644,
  53                 .child = NULL,
  54                 .proc_handler = &proc_dointvec,
  55                 .strategy = &sysctl_intvec,
  56         }, {
  57                 .ctl_name = VM_LOWMEM_NOTIFY_HIGH_PAGES,
  58                 .procname = "lowmem_notify_high_pages",
  59                 .data = &notify_high_pages,
  60                 .maxlen = sizeof(long),
  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_FREE_PAGES,
  96                 .procname = "lowmem_free_pages",
  97                 .data = &lowmem_free_pages,
  98                 .maxlen = sizeof(unsigned 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 kobj_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 kobject *kobj,
 125                                   struct kobj_attribute *attr, char *page)
 126 {
 127         return sprintf(page, "%u\n", low_watermark_reached);
 128 }
 129
 130 static ssize_t high_watermark_show(struct kobject *kobj,
 131                                    struct kobj_attribute *attr, char *page)
 132 {
 133         return sprintf(page, "%u\n", high_watermark_reached);
 134 }
 135
 136 KERNEL_ATTR_RO(low_watermark);
 137 KERNEL_ATTR_RO(high_watermark);
 138
 139 static void low_watermark_state(int new_state)
 140 {
 141         if (low_watermark_reached != new_state) {
 142                 low_watermark_reached = new_state;
 143                 sysfs_notify(kernel_kobj, NULL, "low_watermark");
 144         }
 145 }
 146
 147 static void high_watermark_state(int new_state)
 148 {
 149         if (high_watermark_reached != new_state) {
 150                 high_watermark_reached = new_state;
 151                 sysfs_notify(kernel_kobj, NULL, "high_watermark");
 152         }
 153 }
 154
 155 static int low_vm_enough_memory(long pages)
 156 {
 157         unsigned long free, allowed;
 158         int cap_sys_admin = 0, notify;
 159
 160         if (cap_capable(current, CAP_SYS_ADMIN) == 0)
 161                 cap_sys_admin = 1;
 162
 163         allowed = totalram_pages - hugetlb_total_pages();
 164         allowed_pages = allowed;
 165
 166         /* We activate ourselves only after both parameters have been
 167          * configured. */
 168         if (deny_pages == 0 || notify_low_pages == 0 || notify_high_pages == 0)
 169                 return  __vm_enough_memory(pages, cap_sys_admin);
 170
 171         vm_acct_memory(pages);
 172
 173         /* Easily freed pages when under VM pressure or direct reclaim */
 174         free = global_page_state(NR_FILE_PAGES);
 175         free += nr_swap_pages;
 176         free += global_page_state(NR_SLAB_RECLAIMABLE);
 177
 178         if (likely(free > notify_low_pages))
 179                 goto enough_memory;
 180
 181         /* No luck, lets make it more expensive and try again.. */
 182         free += nr_free_pages();
 183
 184         if (free < deny_pages) {
 185                 int i;
 186
 187                 lowmem_free_pages = free;
 188                 low_watermark_state(1);
 189                 high_watermark_state(1);
 190                 /* Memory allocations by root are always allowed */
 191                 if (cap_sys_admin)
 192                         return 0;
 193
 194                 /* OOM unkillable process is allowed to consume memory */
 195                 if (current->oomkilladj == OOM_DISABLE)
 196                         return 0;
 197
 198                 /* uids from allowed_uids vector are also allowed no matter what */
 199                 for (i = 0; i < LOWMEM_MAX_UIDS && allowed_uids[i]; i++)
 200                         if (current->uid == allowed_uids[i])
 201                                 return 0;
 202
 203                 vm_unacct_memory(pages);
 204                 if (printk_ratelimit()) {
 205                         printk(MY_NAME ": denying memory allocation to process %d (%s)\n",
 206                                current->pid, current->comm);
 207                 }
 208                 return -ENOMEM;
 209         }
 210
 211 enough_memory:
 212         /* See if we need to notify level 1 */
 213         low_watermark_state(free < notify_low_pages);
 214
 215         /*
 216          * In the level 2 notification case things are more complicated,
 217          * as the level that we drop the state and send a notification
 218          * should be lower than when it is first triggered. Having this
 219          * on the same watermark level ends up bouncing back and forth
 220          * when applications are being stupid.
 221          */
 222         notify = free < notify_high_pages;
 223         if (notify || free - nr_decay_pages > notify_high_pages)
 224                 high_watermark_state(notify);
 225
 226         /* We have plenty of memory */
 227         lowmem_free_pages = free;
 228         return 0;
 229 }
 230
 231 static struct security_operations lowmem_security_ops = {
 232         /* Use the capability functions for some of the hooks */
 233         .ptrace = cap_ptrace,
 234         .capget = cap_capget,
 235         .capset_check = cap_capset_check,
 236         .capset_set = cap_capset_set,
 237         .capable = cap_capable,
 238
 239         .bprm_apply_creds = cap_bprm_apply_creds,
 240         .bprm_set_security = cap_bprm_set_security,
 241
 242         .task_post_setuid = cap_task_post_setuid,
 243         .task_reparent_to_init = cap_task_reparent_to_init,
 244         .vm_enough_memory = low_vm_enough_memory,
 245 };
 246
 247 static struct ctl_table_header *lowmem_table_header;
 248 /* flag to keep track of how we were registered */
 249 static int secondary;
 250
 251 static struct attribute *lowmem_attrs[] = {
 252         &low_watermark_attr.attr,
 253         &high_watermark_attr.attr,
 254         NULL,
 255 };
 256
 257 static struct attribute_group lowmem_attr_group = {
 258         .attrs  = lowmem_attrs,
 259 };
 260
 261 static int __init lowmem_init(void)
 262 {
 263         int r;
 264
 265         /* register ourselves with the security framework */
 266         if (register_security(&lowmem_security_ops)) {
 267                 printk(KERN_ERR MY_NAME ": Failure registering with the kernel\n");
 268                 /* try registering with primary module */
 269                 if (mod_reg_security(MY_NAME, &lowmem_security_ops)) {
 270                         printk(KERN_ERR ": Failure registering with the primary"
 271                                "security module.\n");
 272                         return -EINVAL;
 273                 }
 274                 secondary = 1;
 275         }
 276
 277         /* initialize the uids vector */
 278         memset(allowed_uids, 0, sizeof(allowed_uids));
 279
 280         lowmem_table_header = register_sysctl_table(lowmem_root_table);
 281         if (unlikely(!lowmem_table_header))
 282                 return -EPERM;
 283
 284         r = sysfs_create_group(kernel_kobj,
 285                                &lowmem_attr_group);
 286         if (unlikely(r))
 287                 return r;
 288
 289         printk(KERN_INFO MY_NAME ": Module initialized.\n");
 290
 291         return 0;
 292 }
 293
 294 static void __exit lowmem_exit(void)
 295 {
 296         /* remove ourselves from the security framework */
 297         if (secondary) {
 298                 if (mod_unreg_security(MY_NAME, &lowmem_security_ops))
 299                         printk(KERN_ERR MY_NAME ": Failure unregistering "
 300                                "with the primary security module.\n");
 301         } else {
 302                 if (unregister_security(&lowmem_security_ops)) {
 303                         printk(KERN_ERR MY_NAME ": Failure unregistering "
 304                                "with the kernel.\n");
 305                 }
 306         }
 307
 308         unregister_sysctl_table(lowmem_table_header);
 309
 310         sysfs_remove_group(kernel_kobj, &lowmem_attr_group);
 311
 312         printk(KERN_INFO MY_NAME ": Module removed.\n");
 313 }
 314
 315 module_init(lowmem_init);
 316 module_exit(lowmem_exit);
 317
 318 MODULE_DESCRIPTION("Low watermark LSM module");
 319 MODULE_LICENSE("GPL");