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 /* ima_read_write_check - reflect possible reading/writing errors in the PCR.
  89  *
  90  * When opening a file for read, if the file is already open for write,
  91  * the file could change, resulting in a file measurement error.
  92  *
  93  * Opening a file for write, if the file is already open for read, results
  94  * in a time of measure, time of use (ToMToU) error.
  95  *
  96  * In either case invalidate the PCR.
  97  */
  98 enum iint_pcr_error { TOMTOU, OPEN_WRITERS };
  99 static void ima_read_write_check(enum iint_pcr_error error,
 100                                  struct ima_iint_cache *iint,
 101                                  struct inode *inode,
 102                                  const unsigned char *filename)
 103 {
 104         switch (error) {
 105         case TOMTOU:
 106                 if (iint->readcount > 0)
 107                         ima_add_violation(inode, filename, "invalid_pcr",
 108                                           "ToMToU");
 109                 break;
 110         case OPEN_WRITERS:
 111                 if (iint->writecount > 0)
 112                         ima_add_violation(inode, filename, "invalid_pcr",
 113                                           "open_writers");
 114                 break;
 115         }
 116 }
 117
 118 /*
 119  * Update the counts given an fmode_t
 120  */
 121 static void ima_inc_counts(struct ima_iint_cache *iint, fmode_t mode)
 122 {
 123         BUG_ON(!mutex_is_locked(&iint->mutex));
 124
 125         iint->opencount++;
 126         if ((mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ)
 127                 iint->readcount++;
 128         if (mode & FMODE_WRITE)
 129                 iint->writecount++;
 130 }
 131
 132 /*
 133  * ima_counts_get - increment file counts
 134  *
 135  * Maintain read/write counters for all files, but only
 136  * invalidate the PCR for measured files:
 137  *      - Opening a file for write when already open for read,
 138  *        results in a time of measure, time of use (ToMToU) error.
 139  *      - Opening a file for read when already open for write,
 140  *        could result in a file measurement error.
 141  *
 142  */
 143 void ima_counts_get(struct file *file)
 144 {
 145         struct dentry *dentry = file->f_path.dentry;
 146         struct inode *inode = dentry->d_inode;
 147         fmode_t mode = file->f_mode;
 148         struct ima_iint_cache *iint;
 149         int rc;
 150
 151         if (!ima_initialized || !S_ISREG(inode->i_mode))
 152                 return;
 153         iint = ima_iint_find_get(inode);
 154         if (!iint)
 155                 return;
 156         mutex_lock(&iint->mutex);
 157         rc = ima_must_measure(iint, inode, MAY_READ, FILE_CHECK);
 158         if (rc < 0)
 159                 goto out;
 160
 161         if (mode & FMODE_WRITE) {
 162                 ima_read_write_check(TOMTOU, iint, inode, dentry->d_name.name);
 163                 goto out;
 164         }
 165         ima_read_write_check(OPEN_WRITERS, iint, inode, dentry->d_name.name);
 166 out:
 167         ima_inc_counts(iint, file->f_mode);
 168         mutex_unlock(&iint->mutex);
 169
 170         kref_put(&iint->refcount, iint_free);
 171 }
 172
 173 /*
 174  * Decrement ima counts
 175  */
 176 static void ima_dec_counts(struct ima_iint_cache *iint, struct inode *inode,
 177                            struct file *file)
 178 {
 179         mode_t mode = file->f_mode;
 180         BUG_ON(!mutex_is_locked(&iint->mutex));
 181
 182         iint->opencount--;
 183         if ((mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ)
 184                 iint->readcount--;
 185         if (mode & FMODE_WRITE) {
 186                 iint->writecount--;
 187                 if (iint->writecount == 0) {
 188                         if (iint->version != inode->i_version)
 189                                 iint->flags &= ~IMA_MEASURED;
 190                 }
 191         }
 192
 193         if (((iint->opencount < 0) ||
 194              (iint->readcount < 0) ||
 195              (iint->writecount < 0)) &&
 196             !ima_limit_imbalance(file)) {
 197                 printk(KERN_INFO "%s: open/free imbalance (r:%ld w:%ld o:%ld)\n",
 198                        __func__, iint->readcount, iint->writecount,
 199                        iint->opencount);
 200                 dump_stack();
 201         }
 202 }
 203
 204 /**
 205  * ima_file_free - called on __fput()
 206  * @file: pointer to file structure being freed
 207  *
 208  * Flag files that changed, based on i_version;
 209  * and decrement the iint readcount/writecount.
 210  */
 211 void ima_file_free(struct file *file)
 212 {
 213         struct inode *inode = file->f_dentry->d_inode;
 214         struct ima_iint_cache *iint;
 215
 216         if (!ima_initialized || !S_ISREG(inode->i_mode))
 217                 return;
 218         iint = ima_iint_find_get(inode);
 219         if (!iint)
 220                 return;
 221
 222         mutex_lock(&iint->mutex);
 223         ima_dec_counts(iint, inode, file);
 224         mutex_unlock(&iint->mutex);
 225         kref_put(&iint->refcount, iint_free);
 226 }
 227
 228 static int process_measurement(struct file *file, const unsigned char *filename,
 229                                int mask, int function)
 230 {
 231         struct inode *inode = file->f_dentry->d_inode;
 232         struct ima_iint_cache *iint;
 233         int rc;
 234
 235         if (!ima_initialized || !S_ISREG(inode->i_mode))
 236                 return 0;
 237         iint = ima_iint_find_get(inode);
 238         if (!iint)
 239                 return -ENOMEM;
 240
 241         mutex_lock(&iint->mutex);
 242         rc = ima_must_measure(iint, inode, mask, function);
 243         if (rc != 0)
 244                 goto out;
 245
 246         rc = ima_collect_measurement(iint, file);
 247         if (!rc)
 248                 ima_store_measurement(iint, file, filename);
 249 out:
 250         mutex_unlock(&iint->mutex);
 251         kref_put(&iint->refcount, iint_free);
 252         return rc;
 253 }
 254
 255 /**
 256  * ima_file_mmap - based on policy, collect/store measurement.
 257  * @file: pointer to the file to be measured (May be NULL)
 258  * @prot: contains the protection that will be applied by the kernel.
 259  *
 260  * Measure files being mmapped executable based on the ima_must_measure()
 261  * policy decision.
 262  *
 263  * Return 0 on success, an error code on failure.
 264  * (Based on the results of appraise_measurement().)
 265  */
 266 int ima_file_mmap(struct file *file, unsigned long prot)
 267 {
 268         int rc;
 269
 270         if (!file)
 271                 return 0;
 272         if (prot & PROT_EXEC)
 273                 rc = process_measurement(file, file->f_dentry->d_name.name,
 274                                          MAY_EXEC, FILE_MMAP);
 275         return 0;
 276 }
 277
 278 /**
 279  * ima_bprm_check - based on policy, collect/store measurement.
 280  * @bprm: contains the linux_binprm structure
 281  *
 282  * The OS protects against an executable file, already open for write,
 283  * from being executed in deny_write_access() and an executable file,
 284  * already open for execute, from being modified in get_write_access().
 285  * So we can be certain that what we verify and measure here is actually
 286  * what is being executed.
 287  *
 288  * Return 0 on success, an error code on failure.
 289  * (Based on the results of appraise_measurement().)
 290  */
 291 int ima_bprm_check(struct linux_binprm *bprm)
 292 {
 293         int rc;
 294
 295         rc = process_measurement(bprm->file, bprm->filename,
 296                                  MAY_EXEC, BPRM_CHECK);
 297         return 0;
 298 }
 299
 300 /**
 301  * ima_path_check - based on policy, collect/store measurement.
 302  * @file: pointer to the file to be measured
 303  * @mask: contains MAY_READ, MAY_WRITE or MAY_EXECUTE
 304  *
 305  * Measure files based on the ima_must_measure() policy decision.
 306  *
 307  * Always return 0 and audit dentry_open failures.
 308  * (Return code will be based upon measurement appraisal.)
 309  */
 310 int ima_file_check(struct file *file, int mask)
 311 {
 312         int rc;
 313
 314         rc = process_measurement(file, file->f_dentry->d_name.name,
 315                                  mask & (MAY_READ | MAY_WRITE | MAY_EXEC),
 316                                  FILE_CHECK);
 317         return 0;
 318 }
 319 EXPORT_SYMBOL_GPL(ima_file_check);
 320
 321 static int __init init_ima(void)
 322 {
 323         int error;
 324
 325         error = ima_init();
 326         ima_initialized = 1;
 327         return error;
 328 }
 329
 330 static void __exit cleanup_ima(void)
 331 {
 332         ima_cleanup();
 333 }
 334
 335 late_initcall(init_ima);        /* Start IMA after the TPM is available */
 336
 337 MODULE_DESCRIPTION("Integrity Measurement Architecture");
 338 MODULE_LICENSE("GPL");