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 /*
  40  * ima_rdwr_violation_check
  41  *
  42  * Only invalidate the PCR for measured files:
  43  *      - Opening a file for write when already open for read,
  44  *        results in a time of measure, time of use (ToMToU) error.
  45  *      - Opening a file for read when already open for write,
  46  *        could result in a file measurement error.
  47  *
  48  */
  49 static void ima_rdwr_violation_check(struct file *file)
  50 {
  51         struct dentry *dentry = file->f_path.dentry;
  52         struct inode *inode = dentry->d_inode;
  53         fmode_t mode = file->f_mode;
  54         int rc;
  55         bool send_tomtou = false, send_writers = false;
  56
  57         if (!S_ISREG(inode->i_mode) || !ima_initialized)
  58                 return;
  59
  60         mutex_lock(&inode->i_mutex);    /* file metadata: permissions, xattr */
  61
  62         if (mode & FMODE_WRITE) {
  63                 if (atomic_read(&inode->i_readcount) && IS_IMA(inode))
  64                         send_tomtou = true;
  65                 goto out;
  66         }
  67
  68         rc = ima_must_measure(inode, MAY_READ, FILE_CHECK);
  69         if (rc < 0)
  70                 goto out;
  71
  72         if (atomic_read(&inode->i_writecount) > 0)
  73                 send_writers = true;
  74 out:
  75         mutex_unlock(&inode->i_mutex);
  76
  77         if (send_tomtou)
  78                 ima_add_violation(inode, dentry->d_name.name, "invalid_pcr",
  79                                   "ToMToU");
  80         if (send_writers)
  81                 ima_add_violation(inode, dentry->d_name.name, "invalid_pcr",
  82                                   "open_writers");
  83 }
  84
  85 static void ima_check_last_writer(struct ima_iint_cache *iint,
  86                                   struct inode *inode,
  87                                   struct file *file)
  88 {
  89         mode_t mode = file->f_mode;
  90
  91         mutex_lock(&iint->mutex);
  92         if (mode & FMODE_WRITE &&
  93             atomic_read(&inode->i_writecount) == 1 &&
  94             iint->version != inode->i_version)
  95                 iint->flags &= ~IMA_MEASURED;
  96         mutex_unlock(&iint->mutex);
  97 }
  98
  99 /**
 100  * ima_file_free - called on __fput()
 101  * @file: pointer to file structure being freed
 102  *
 103  * Flag files that changed, based on i_version
 104  */
 105 void ima_file_free(struct file *file)
 106 {
 107         struct inode *inode = file->f_dentry->d_inode;
 108         struct ima_iint_cache *iint;
 109
 110         if (!iint_initialized || !S_ISREG(inode->i_mode))
 111                 return;
 112
 113         iint = ima_iint_find(inode);
 114         if (!iint)
 115                 return;
 116
 117         ima_check_last_writer(iint, inode, file);
 118 }
 119
 120 static int process_measurement(struct file *file, const unsigned char *filename,
 121                                int mask, int function)
 122 {
 123         struct inode *inode = file->f_dentry->d_inode;
 124         struct ima_iint_cache *iint;
 125         int rc = 0;
 126
 127         if (!ima_initialized || !S_ISREG(inode->i_mode))
 128                 return 0;
 129
 130         rc = ima_must_measure(inode, mask, function);
 131         if (rc != 0)
 132                 return rc;
 133 retry:
 134         iint = ima_iint_find(inode);
 135         if (!iint) {
 136                 rc = ima_inode_alloc(inode);
 137                 if (!rc || rc == -EEXIST)
 138                         goto retry;
 139                 return rc;
 140         }
 141
 142         mutex_lock(&iint->mutex);
 143
 144         rc = iint->flags & IMA_MEASURED ? 1 : 0;
 145         if (rc != 0)
 146                 goto out;
 147
 148         rc = ima_collect_measurement(iint, file);
 149         if (!rc)
 150                 ima_store_measurement(iint, file, filename);
 151 out:
 152         mutex_unlock(&iint->mutex);
 153         return rc;
 154 }
 155
 156 /**
 157  * ima_file_mmap - based on policy, collect/store measurement.
 158  * @file: pointer to the file to be measured (May be NULL)
 159  * @prot: contains the protection that will be applied by the kernel.
 160  *
 161  * Measure files being mmapped executable based on the ima_must_measure()
 162  * policy decision.
 163  *
 164  * Return 0 on success, an error code on failure.
 165  * (Based on the results of appraise_measurement().)
 166  */
 167 int ima_file_mmap(struct file *file, unsigned long prot)
 168 {
 169         int rc;
 170
 171         if (!file)
 172                 return 0;
 173         if (prot & PROT_EXEC)
 174                 rc = process_measurement(file, file->f_dentry->d_name.name,
 175                                          MAY_EXEC, FILE_MMAP);
 176         return 0;
 177 }
 178
 179 /**
 180  * ima_bprm_check - based on policy, collect/store measurement.
 181  * @bprm: contains the linux_binprm structure
 182  *
 183  * The OS protects against an executable file, already open for write,
 184  * from being executed in deny_write_access() and an executable file,
 185  * already open for execute, from being modified in get_write_access().
 186  * So we can be certain that what we verify and measure here is actually
 187  * what is being executed.
 188  *
 189  * Return 0 on success, an error code on failure.
 190  * (Based on the results of appraise_measurement().)
 191  */
 192 int ima_bprm_check(struct linux_binprm *bprm)
 193 {
 194         int rc;
 195
 196         rc = process_measurement(bprm->file, bprm->filename,
 197                                  MAY_EXEC, BPRM_CHECK);
 198         return 0;
 199 }
 200
 201 /**
 202  * ima_path_check - based on policy, collect/store measurement.
 203  * @file: pointer to the file to be measured
 204  * @mask: contains MAY_READ, MAY_WRITE or MAY_EXECUTE
 205  *
 206  * Measure files based on the ima_must_measure() policy decision.
 207  *
 208  * Always return 0 and audit dentry_open failures.
 209  * (Return code will be based upon measurement appraisal.)
 210  */
 211 int ima_file_check(struct file *file, int mask)
 212 {
 213         int rc;
 214
 215         ima_rdwr_violation_check(file);
 216         rc = process_measurement(file, file->f_dentry->d_name.name,
 217                                  mask & (MAY_READ | MAY_WRITE | MAY_EXEC),
 218                                  FILE_CHECK);
 219         return 0;
 220 }
 221 EXPORT_SYMBOL_GPL(ima_file_check);
 222
 223 static int __init init_ima(void)
 224 {
 225         int error;
 226
 227         error = ima_init();
 228         ima_initialized = 1;
 229         return error;
 230 }
 231
 232 static void __exit cleanup_ima(void)
 233 {
 234         ima_cleanup();
 235 }
 236
 237 late_initcall(init_ima);        /* Start IMA after the TPM is available */
 238
 239 MODULE_DESCRIPTION("Integrity Measurement Architecture");
 240 MODULE_LICENSE("GPL");