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