security/integrity/ima/ima_main.c

   1 /*
   2  * Copyright (C) 2005,2006,2007,2008 IBM Corporation
   3  *
   4  * Authors:
   5  * Reiner Sailer <sailer@watson.ibm.com>
   6  * Serge Hallyn <serue@us.ibm.com>
   7  * Kylene Hall <kylene@us.ibm.com>
   8  * Mimi Zohar <zohar@us.ibm.com>
   9  *
  10  * This program is free software; you can redistribute it and/or
  11  * modify it under the terms of the GNU General Public License as
  12  * published by the Free Software Foundation, version 2 of the
  13  * License.
  14  *
  15  * File: ima_main.c
  16  *      implements the IMA hooks: ima_bprm_check, ima_file_mmap,
  17  *      and ima_file_check.
  18  */
  19 #include <linux/module.h>
  20 #include <linux/file.h>
  21 #include <linux/binfmts.h>
  22 #include <linux/mount.h>
  23 #include <linux/mman.h>
  24 #include <linux/slab.h>
  25
  26 #include "ima.h"
  27
  28 int ima_initialized;
  29
  30 char *ima_hash = "sha1";
  31 static int __init hash_setup(char *str)
  32 {
  33         if (strncmp(str, "md5", 3) == 0)
  34                 ima_hash = "md5";
  35         return 1;
  36 }
  37 __setup("ima_hash=", hash_setup);
  38
  39 struct ima_imbalance {
  40         struct hlist_node node;
  41         unsigned long fsmagic;
  42 };
  43
  44 /*
  45  * ima_limit_imbalance - emit one imbalance message per filesystem type
  46  *
  47  * Maintain list of filesystem types that do not measure files properly.
  48  * Return false if unknown, true if known.
  49  */
  50 static bool ima_limit_imbalance(struct file *file)
  51 {
  52         static DEFINE_SPINLOCK(ima_imbalance_lock);
  53         static HLIST_HEAD(ima_imbalance_list);
  54
  55         struct super_block *sb = file->f_dentry->d_sb;
  56         struct ima_imbalance *entry;
  57         struct hlist_node *node;
  58         bool found = false;
  59
  60         rcu_read_lock();
  61         hlist_for_each_entry_rcu(entry, node, &ima_imbalance_list, node) {
  62                 if (entry->fsmagic == sb->s_magic) {
  63                         found = true;
  64                         break;
  65                 }
  66         }
  67         rcu_read_unlock();
  68         if (found)
  69                 goto out;
  70
  71         entry = kmalloc(sizeof(*entry), GFP_NOFS);
  72         if (!entry)
  73                 goto out;
  74         entry->fsmagic = sb->s_magic;
  75         spin_lock(&ima_imbalance_lock);
  76         /*
  77          * we could have raced and something else might have added this fs
  78          * to the list, but we don't really care
  79          */
  80         hlist_add_head_rcu(&entry->node, &ima_imbalance_list);
  81         spin_unlock(&ima_imbalance_lock);
  82         printk(KERN_INFO "IMA: unmeasured files on fsmagic: %lX\n",
  83                entry->fsmagic);
  84 out:
  85         return found;
  86 }
  87
  88 /*
  89  * ima_counts_get - increment file counts
  90  *
  91  * Maintain read/write counters for all files, but only
  92  * invalidate the PCR for measured files:
  93  *      - Opening a file for write when already open for read,
  94  *        results in a time of measure, time of use (ToMToU) error.
  95  *      - Opening a file for read when already open for write,
  96  *        could result in a file measurement error.
  97  *
  98  */
  99 void ima_counts_get(struct file *file)
 100 {
 101         struct dentry *dentry = file->f_path.dentry;
 102         struct inode *inode = dentry->d_inode;
 103         fmode_t mode = file->f_mode;
 104         int rc;
 105         bool send_tomtou = false, send_writers = false;
 106
 107         if (!S_ISREG(inode->i_mode))
 108                 return;
 109
 110         spin_lock(&inode->i_lock);
 111
 112         if (!ima_initialized)
 113                 goto out;
 114
 115         if (mode & FMODE_WRITE) {
 116                 if (inode->i_readcount && IS_IMA(inode))
 117                         send_tomtou = true;
 118                 goto out;
 119         }
 120
 121         rc = ima_must_measure(NULL, inode, MAY_READ, FILE_CHECK);
 122         if (rc < 0)
 123                 goto out;
 124
 125         if (atomic_read(&inode->i_writecount) > 0)
 126                 send_writers = true;
 127 out:
 128         /* remember the vfs deals with i_writecount */
 129         if ((mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ)
 130                 inode->i_readcount++;
 131
 132         spin_unlock(&inode->i_lock);
 133
 134         if (send_tomtou)
 135                 ima_add_violation(inode, dentry->d_name.name, "invalid_pcr",
 136                                   "ToMToU");
 137         if (send_writers)
 138                 ima_add_violation(inode, dentry->d_name.name, "invalid_pcr",
 139                                   "open_writers");
 140 }
 141
 142 /*
 143  * Decrement ima counts
 144  */
 145 static void ima_dec_counts(struct inode *inode, struct file *file)
 146 {
 147         mode_t mode = file->f_mode;
 148
 149         assert_spin_locked(&inode->i_lock);
 150
 151         if ((mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ) {
 152                 if (unlikely(inode->i_readcount == 0)) {
 153                         if (!ima_limit_imbalance(file)) {
 154                                 printk(KERN_INFO "%s: open/free imbalance (r:%u)\n",
 155                                        __func__, inode->i_readcount);
 156                                 dump_stack();
 157                         }
 158                         return;
 159                 }
 160                 inode->i_readcount--;
 161         }
 162 }
 163
 164 static void ima_check_last_writer(struct ima_iint_cache *iint,
 165                                   struct inode *inode,
 166                                   struct file *file)
 167 {
 168         mode_t mode = file->f_mode;
 169
 170         BUG_ON(!mutex_is_locked(&iint->mutex));
 171         assert_spin_locked(&inode->i_lock);
 172
 173         if (mode & FMODE_WRITE &&
 174             atomic_read(&inode->i_writecount) == 1 &&
 175             iint->version != inode->i_version)
 176                 iint->flags &= ~IMA_MEASURED;
 177 }
 178
 179 static void ima_file_free_iint(struct ima_iint_cache *iint, struct inode *inode,
 180                                struct file *file)
 181 {
 182         mutex_lock(&iint->mutex);
 183         spin_lock(&inode->i_lock);
 184
 185         ima_dec_counts(inode, file);
 186         ima_check_last_writer(iint, inode, file);
 187
 188         spin_unlock(&inode->i_lock);
 189         mutex_unlock(&iint->mutex);
 190 }
 191
 192 static void ima_file_free_noiint(struct inode *inode, struct file *file)
 193 {
 194         spin_lock(&inode->i_lock);
 195
 196         ima_dec_counts(inode, file);
 197
 198         spin_unlock(&inode->i_lock);
 199 }
 200
 201 /**
 202  * ima_file_free - called on __fput()
 203  * @file: pointer to file structure being freed
 204  *
 205  * Flag files that changed, based on i_version;
 206  * and decrement the i_readcount.
 207  */
 208 void ima_file_free(struct file *file)
 209 {
 210         struct inode *inode = file->f_dentry->d_inode;
 211         struct ima_iint_cache *iint;
 212
 213         if (!iint_initialized || !S_ISREG(inode->i_mode))
 214                 return;
 215
 216         iint = ima_iint_find(inode);
 217
 218         if (iint)
 219                 ima_file_free_iint(iint, inode, file);
 220         else
 221                 ima_file_free_noiint(inode, file);
 222
 223 }
 224
 225 static int process_measurement(struct file *file, const unsigned char *filename,
 226                                int mask, int function)
 227 {
 228         struct inode *inode = file->f_dentry->d_inode;
 229         struct ima_iint_cache *iint;
 230         int rc = 0;
 231
 232         if (!ima_initialized || !S_ISREG(inode->i_mode))
 233                 return 0;
 234
 235         rc = ima_must_measure(NULL, inode, mask, function);
 236         if (rc != 0)
 237                 return rc;
 238 retry:
 239         iint = ima_iint_find(inode);
 240         if (!iint) {
 241                 rc = ima_inode_alloc(inode);
 242                 if (!rc || rc == -EEXIST)
 243                         goto retry;
 244                 return rc;
 245         }
 246
 247         mutex_lock(&iint->mutex);
 248
 249         rc = ima_must_measure(iint, inode, mask, function);
 250         if (rc != 0)
 251                 goto out;
 252
 253         rc = ima_collect_measurement(iint, file);
 254         if (!rc)
 255                 ima_store_measurement(iint, file, filename);
 256 out:
 257         mutex_unlock(&iint->mutex);
 258         return rc;
 259 }
 260
 261 /**
 262  * ima_file_mmap - based on policy, collect/store measurement.
 263  * @file: pointer to the file to be measured (May be NULL)
 264  * @prot: contains the protection that will be applied by the kernel.
 265  *
 266  * Measure files being mmapped executable based on the ima_must_measure()
 267  * policy decision.
 268  *
 269  * Return 0 on success, an error code on failure.
 270  * (Based on the results of appraise_measurement().)
 271  */
 272 int ima_file_mmap(struct file *file, unsigned long prot)
 273 {
 274         int rc;
 275
 276         if (!file)
 277                 return 0;
 278         if (prot & PROT_EXEC)
 279                 rc = process_measurement(file, file->f_dentry->d_name.name,
 280                                          MAY_EXEC, FILE_MMAP);
 281         return 0;
 282 }
 283
 284 /**
 285  * ima_bprm_check - based on policy, collect/store measurement.
 286  * @bprm: contains the linux_binprm structure
 287  *
 288  * The OS protects against an executable file, already open for write,
 289  * from being executed in deny_write_access() and an executable file,
 290  * already open for execute, from being modified in get_write_access().
 291  * So we can be certain that what we verify and measure here is actually
 292  * what is being executed.
 293  *
 294  * Return 0 on success, an error code on failure.
 295  * (Based on the results of appraise_measurement().)
 296  */
 297 int ima_bprm_check(struct linux_binprm *bprm)
 298 {
 299         int rc;
 300
 301         rc = process_measurement(bprm->file, bprm->filename,
 302                                  MAY_EXEC, BPRM_CHECK);
 303         return 0;
 304 }
 305
 306 /**
 307  * ima_path_check - based on policy, collect/store measurement.
 308  * @file: pointer to the file to be measured
 309  * @mask: contains MAY_READ, MAY_WRITE or MAY_EXECUTE
 310  *
 311  * Measure files based on the ima_must_measure() policy decision.
 312  *
 313  * Always return 0 and audit dentry_open failures.
 314  * (Return code will be based upon measurement appraisal.)
 315  */
 316 int ima_file_check(struct file *file, int mask)
 317 {
 318         int rc;
 319
 320         rc = process_measurement(file, file->f_dentry->d_name.name,
 321                                  mask & (MAY_READ | MAY_WRITE | MAY_EXEC),
 322                                  FILE_CHECK);
 323         return 0;
 324 }
 325 EXPORT_SYMBOL_GPL(ima_file_check);
 326
 327 static int __init init_ima(void)
 328 {
 329         int error;
 330
 331         error = ima_init();
 332         ima_initialized = 1;
 333         return error;
 334 }
 335
 336 static void __exit cleanup_ima(void)
 337 {
 338         ima_cleanup();
 339 }
 340
 341 late_initcall(init_ima);        /* Start IMA after the TPM is available */
 342
 343 MODULE_DESCRIPTION("Integrity Measurement Architecture");
 344 MODULE_LICENSE("GPL");