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_path_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         const char *op = "hash_setup";
  33         const char *hash = "sha1";
  34         int result = 0;
  35         int audit_info = 0;
  36
  37         if (strncmp(str, "md5", 3) == 0) {
  38                 hash = "md5";
  39                 ima_hash = str;
  40         } else if (strncmp(str, "sha1", 4) != 0) {
  41                 hash = "invalid_hash_type";
  42                 result = 1;
  43         }
  44         integrity_audit_msg(AUDIT_INTEGRITY_HASH, NULL, NULL, op, hash,
  45                             result, audit_info);
  46         return 1;
  47 }
  48 __setup("ima_hash=", hash_setup);
  49
  50 /**
  51  * ima_file_free - called on __fput()
  52  * @file: pointer to file structure being freed
  53  *
  54  * Flag files that changed, based on i_version;
  55  * and decrement the iint readcount/writecount.
  56  */
  57 void ima_file_free(struct file *file)
  58 {
  59         struct inode *inode = file->f_dentry->d_inode;
  60         struct ima_iint_cache *iint;
  61
  62         if (!ima_initialized || !S_ISREG(inode->i_mode))
  63                 return;
  64         iint = ima_iint_find_get(inode);
  65         if (!iint)
  66                 return;
  67
  68         mutex_lock(&iint->mutex);
  69         if ((file->f_mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ)
  70                 iint->readcount--;
  71
  72         if (file->f_mode & FMODE_WRITE) {
  73                 iint->writecount--;
  74                 if (iint->writecount == 0) {
  75                         if (iint->version != inode->i_version)
  76                                 iint->flags &= ~IMA_MEASURED;
  77                 }
  78         }
  79         mutex_unlock(&iint->mutex);
  80         kref_put(&iint->refcount, iint_free);
  81 }
  82
  83 /* ima_read_write_check - reflect possible reading/writing errors in the PCR.
  84  *
  85  * When opening a file for read, if the file is already open for write,
  86  * the file could change, resulting in a file measurement error.
  87  *
  88  * Opening a file for write, if the file is already open for read, results
  89  * in a time of measure, time of use (ToMToU) error.
  90  *
  91  * In either case invalidate the PCR.
  92  */
  93 enum iint_pcr_error { TOMTOU, OPEN_WRITERS };
  94 static void ima_read_write_check(enum iint_pcr_error error,
  95                                  struct ima_iint_cache *iint,
  96                                  struct inode *inode,
  97                                  const unsigned char *filename)
  98 {
  99         switch (error) {
 100         case TOMTOU:
 101                 if (iint->readcount > 0)
 102                         ima_add_violation(inode, filename, "invalid_pcr",
 103                                           "ToMToU");
 104                 break;
 105         case OPEN_WRITERS:
 106                 if (iint->writecount > 0)
 107                         ima_add_violation(inode, filename, "invalid_pcr",
 108                                           "open_writers");
 109                 break;
 110         }
 111 }
 112
 113 static int get_path_measurement(struct ima_iint_cache *iint, struct file *file,
 114                                 const unsigned char *filename)
 115 {
 116         int rc = 0;
 117
 118         if (IS_ERR(file)) {
 119                 pr_info("%s dentry_open failed\n", filename);
 120                 return rc;
 121         }
 122         iint->readcount++;
 123
 124         rc = ima_collect_measurement(iint, file);
 125         if (!rc)
 126                 ima_store_measurement(iint, file, filename);
 127         return rc;
 128 }
 129
 130 /**
 131  * ima_path_check - based on policy, collect/store measurement.
 132  * @path: contains a pointer to the path to be measured
 133  * @mask: contains MAY_READ, MAY_WRITE or MAY_EXECUTE
 134  *
 135  * Measure the file being open for readonly, based on the
 136  * ima_must_measure() policy decision.
 137  *
 138  * Keep read/write counters for all files, but only
 139  * invalidate the PCR for measured files:
 140  *      - Opening a file for write when already open for read,
 141  *        results in a time of measure, time of use (ToMToU) error.
 142  *      - Opening a file for read when already open for write,
 143  *        could result in a file measurement error.
 144  *
 145  * Return 0 on success, an error code on failure.
 146  * (Based on the results of appraise_measurement().)
 147  */
 148 int ima_path_check(struct path *path, int mask)
 149 {
 150         struct inode *inode = path->dentry->d_inode;
 151         struct ima_iint_cache *iint;
 152         struct file *file = NULL;
 153         int rc;
 154
 155         if (!ima_initialized || !S_ISREG(inode->i_mode))
 156                 return 0;
 157         iint = ima_iint_find_insert_get(inode);
 158         if (!iint)
 159                 return 0;
 160
 161         mutex_lock(&iint->mutex);
 162         if ((mask & MAY_WRITE) || (mask == 0))
 163                 iint->writecount++;
 164         else if (mask & (MAY_READ | MAY_EXEC))
 165                 iint->readcount++;
 166
 167         rc = ima_must_measure(iint, inode, MAY_READ, PATH_CHECK);
 168         if (rc < 0)
 169                 goto out;
 170
 171         if ((mask & MAY_WRITE) || (mask == 0))
 172                 ima_read_write_check(TOMTOU, iint, inode,
 173                                      path->dentry->d_name.name);
 174
 175         if ((mask & (MAY_WRITE | MAY_READ | MAY_EXEC)) != MAY_READ)
 176                 goto out;
 177
 178         ima_read_write_check(OPEN_WRITERS, iint, inode,
 179                              path->dentry->d_name.name);
 180         if (!(iint->flags & IMA_MEASURED)) {
 181                 struct dentry *dentry = dget(path->dentry);
 182                 struct vfsmount *mnt = mntget(path->mnt);
 183
 184                 file = dentry_open(dentry, mnt, O_RDONLY, current->cred);
 185                 rc = get_path_measurement(iint, file, dentry->d_name.name);
 186         }
 187 out:
 188         mutex_unlock(&iint->mutex);
 189         if (file)
 190                 fput(file);
 191         kref_put(&iint->refcount, iint_free);
 192         return 0;
 193 }
 194
 195 static int process_measurement(struct file *file, const unsigned char *filename,
 196                                int mask, int function)
 197 {
 198         struct inode *inode = file->f_dentry->d_inode;
 199         struct ima_iint_cache *iint;
 200         int rc;
 201
 202         if (!ima_initialized || !S_ISREG(inode->i_mode))
 203                 return 0;
 204         iint = ima_iint_find_insert_get(inode);
 205         if (!iint)
 206                 return -ENOMEM;
 207
 208         mutex_lock(&iint->mutex);
 209         rc = ima_must_measure(iint, inode, mask, function);
 210         if (rc != 0)
 211                 goto out;
 212
 213         rc = ima_collect_measurement(iint, file);
 214         if (!rc)
 215                 ima_store_measurement(iint, file, filename);
 216 out:
 217         mutex_unlock(&iint->mutex);
 218         kref_put(&iint->refcount, iint_free);
 219         return rc;
 220 }
 221
 222 /**
 223  * ima_file_mmap - based on policy, collect/store measurement.
 224  * @file: pointer to the file to be measured (May be NULL)
 225  * @prot: contains the protection that will be applied by the kernel.
 226  *
 227  * Measure files being mmapped executable based on the ima_must_measure()
 228  * policy decision.
 229  *
 230  * Return 0 on success, an error code on failure.
 231  * (Based on the results of appraise_measurement().)
 232  */
 233 int ima_file_mmap(struct file *file, unsigned long prot)
 234 {
 235         int rc;
 236
 237         if (!file)
 238                 return 0;
 239         if (prot & PROT_EXEC)
 240                 rc = process_measurement(file, file->f_dentry->d_name.name,
 241                                          MAY_EXEC, FILE_MMAP);
 242         return 0;
 243 }
 244
 245 /**
 246  * ima_bprm_check - based on policy, collect/store measurement.
 247  * @bprm: contains the linux_binprm structure
 248  *
 249  * The OS protects against an executable file, already open for write,
 250  * from being executed in deny_write_access() and an executable file,
 251  * already open for execute, from being modified in get_write_access().
 252  * So we can be certain that what we verify and measure here is actually
 253  * what is being executed.
 254  *
 255  * Return 0 on success, an error code on failure.
 256  * (Based on the results of appraise_measurement().)
 257  */
 258 int ima_bprm_check(struct linux_binprm *bprm)
 259 {
 260         int rc;
 261
 262         rc = process_measurement(bprm->file, bprm->filename,
 263                                  MAY_EXEC, BPRM_CHECK);
 264         return 0;
 265 }
 266
 267 static int __init init_ima(void)
 268 {
 269         int error;
 270
 271         ima_iintcache_init();
 272         error = ima_init();
 273         ima_initialized = 1;
 274         return error;
 275 }
 276
 277 late_initcall(init_ima);        /* Start IMA after the TPM is available */
 278
 279 MODULE_DESCRIPTION("Integrity Measurement Architecture");
 280 MODULE_LICENSE("GPL");