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 (atomic_read(&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                 atomic_inc(&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(atomic_read(&inode->i_readcount) == 0)) {
 153                         if (!ima_limit_imbalance(file)) {
 154                                 printk(KERN_INFO "%s: open/free imbalance (r:%u)\n",
 155                                        __func__,
 156                                        atomic_read(&inode->i_readcount));
 157                                 dump_stack();
 158                         }
 159                         return;
 160                 }
 161                 atomic_dec(&inode->i_readcount);
 162         }
 163 }
 164
 165 static void ima_check_last_writer(struct ima_iint_cache *iint,
 166                                   struct inode *inode,
 167                                   struct file *file)
 168 {
 169         mode_t mode = file->f_mode;
 170
 171         BUG_ON(!mutex_is_locked(&iint->mutex));
 172         assert_spin_locked(&inode->i_lock);
 173
 174         if (mode & FMODE_WRITE &&
 175             atomic_read(&inode->i_writecount) == 1 &&
 176             iint->version != inode->i_version)
 177                 iint->flags &= ~IMA_MEASURED;
 178 }
 179
 180 static void ima_file_free_iint(struct ima_iint_cache *iint, struct inode *inode,
 181                                struct file *file)
 182 {
 183         mutex_lock(&iint->mutex);
 184         spin_lock(&inode->i_lock);
 185
 186         ima_dec_counts(inode, file);
 187         ima_check_last_writer(iint, inode, file);
 188
 189         spin_unlock(&inode->i_lock);
 190         mutex_unlock(&iint->mutex);
 191 }
 192
 193 static void ima_file_free_noiint(struct inode *inode, struct file *file)
 194 {
 195         spin_lock(&inode->i_lock);
 196
 197         ima_dec_counts(inode, file);
 198
 199         spin_unlock(&inode->i_lock);
 200 }
 201
 202 /**
 203  * ima_file_free - called on __fput()
 204  * @file: pointer to file structure being freed
 205  *
 206  * Flag files that changed, based on i_version;
 207  * and decrement the i_readcount.
 208  */
 209 void ima_file_free(struct file *file)
 210 {
 211         struct inode *inode = file->f_dentry->d_inode;
 212         struct ima_iint_cache *iint;
 213
 214         if (!iint_initialized || !S_ISREG(inode->i_mode))
 215                 return;
 216
 217         iint = ima_iint_find(inode);
 218
 219         if (iint)
 220                 ima_file_free_iint(iint, inode, file);
 221         else
 222                 ima_file_free_noiint(inode, file);
 223
 224 }
 225
 226 static int process_measurement(struct file *file, const unsigned char *filename,
 227                                int mask, int function)
 228 {
 229         struct inode *inode = file->f_dentry->d_inode;
 230         struct ima_iint_cache *iint;
 231         int rc = 0;
 232
 233         if (!ima_initialized || !S_ISREG(inode->i_mode))
 234                 return 0;
 235
 236         rc = ima_must_measure(NULL, inode, mask, function);
 237         if (rc != 0)
 238                 return rc;
 239 retry:
 240         iint = ima_iint_find(inode);
 241         if (!iint) {
 242                 rc = ima_inode_alloc(inode);
 243                 if (!rc || rc == -EEXIST)
 244                         goto retry;
 245                 return rc;
 246         }
 247
 248         mutex_lock(&iint->mutex);
 249
 250         rc = ima_must_measure(iint, inode, mask, function);
 251         if (rc != 0)
 252                 goto out;
 253
 254         rc = ima_collect_measurement(iint, file);
 255         if (!rc)
 256                 ima_store_measurement(iint, file, filename);
 257 out:
 258         mutex_unlock(&iint->mutex);
 259         return rc;
 260 }
 261
 262 /**
 263  * ima_file_mmap - based on policy, collect/store measurement.
 264  * @file: pointer to the file to be measured (May be NULL)
 265  * @prot: contains the protection that will be applied by the kernel.
 266  *
 267  * Measure files being mmapped executable based on the ima_must_measure()
 268  * policy decision.
 269  *
 270  * Return 0 on success, an error code on failure.
 271  * (Based on the results of appraise_measurement().)
 272  */
 273 int ima_file_mmap(struct file *file, unsigned long prot)
 274 {
 275         int rc;
 276
 277         if (!file)
 278                 return 0;
 279         if (prot & PROT_EXEC)
 280                 rc = process_measurement(file, file->f_dentry->d_name.name,
 281                                          MAY_EXEC, FILE_MMAP);
 282         return 0;
 283 }
 284
 285 /**
 286  * ima_bprm_check - based on policy, collect/store measurement.
 287  * @bprm: contains the linux_binprm structure
 288  *
 289  * The OS protects against an executable file, already open for write,
 290  * from being executed in deny_write_access() and an executable file,
 291  * already open for execute, from being modified in get_write_access().
 292  * So we can be certain that what we verify and measure here is actually
 293  * what is being executed.
 294  *
 295  * Return 0 on success, an error code on failure.
 296  * (Based on the results of appraise_measurement().)
 297  */
 298 int ima_bprm_check(struct linux_binprm *bprm)
 299 {
 300         int rc;
 301
 302         rc = process_measurement(bprm->file, bprm->filename,
 303                                  MAY_EXEC, BPRM_CHECK);
 304         return 0;
 305 }
 306
 307 /**
 308  * ima_path_check - based on policy, collect/store measurement.
 309  * @file: pointer to the file to be measured
 310  * @mask: contains MAY_READ, MAY_WRITE or MAY_EXECUTE
 311  *
 312  * Measure files based on the ima_must_measure() policy decision.
 313  *
 314  * Always return 0 and audit dentry_open failures.
 315  * (Return code will be based upon measurement appraisal.)
 316  */
 317 int ima_file_check(struct file *file, int mask)
 318 {
 319         int rc;
 320
 321         rc = process_measurement(file, file->f_dentry->d_name.name,
 322                                  mask & (MAY_READ | MAY_WRITE | MAY_EXEC),
 323                                  FILE_CHECK);
 324         return 0;
 325 }
 326 EXPORT_SYMBOL_GPL(ima_file_check);
 327
 328 static int __init init_ima(void)
 329 {
 330         int error;
 331
 332         error = ima_init();
 333         ima_initialized = 1;
 334         return error;
 335 }
 336
 337 static void __exit cleanup_ima(void)
 338 {
 339         ima_cleanup();
 340 }
 341
 342 late_initcall(init_ima);        /* Start IMA after the TPM is available */
 343
 344 MODULE_DESCRIPTION("Integrity Measurement Architecture");
 345 MODULE_LICENSE("GPL");