security/integrity/ima/ima_appraise.c

   1 /*
   2  * Copyright (C) 2011 IBM Corporation
   3  *
   4  * Author:
   5  * Mimi Zohar <zohar@us.ibm.com>
   6  *
   7  * This program is free software; you can redistribute it and/or modify
   8  * it under the terms of the GNU General Public License as published by
   9  * the Free Software Foundation, version 2 of the License.
  10  */
  11 #include <linux/module.h>
  12 #include <linux/file.h>
  13 #include <linux/fs.h>
  14 #include <linux/xattr.h>
  15 #include <linux/magic.h>
  16 #include <linux/ima.h>
  17 #include <linux/evm.h>
  18
  19 #include "ima.h"
  20
  21 static int __init default_appraise_setup(char *str)
  22 {
  23         if (strncmp(str, "off", 3) == 0)
  24                 ima_appraise = 0;
  25         else if (strncmp(str, "fix", 3) == 0)
  26                 ima_appraise = IMA_APPRAISE_FIX;
  27         return 1;
  28 }
  29
  30 __setup("ima_appraise=", default_appraise_setup);
  31
  32 /*
  33  * ima_must_appraise - set appraise flag
  34  *
  35  * Return 1 to appraise
  36  */
  37 int ima_must_appraise(struct inode *inode, enum ima_hooks func, int mask)
  38 {
  39         return 0;
  40 }
  41
  42 static void ima_fix_xattr(struct dentry *dentry,
  43                           struct integrity_iint_cache *iint)
  44 {
  45         iint->digest[0] = IMA_XATTR_DIGEST;
  46         __vfs_setxattr_noperm(dentry, XATTR_NAME_IMA,
  47                               iint->digest, IMA_DIGEST_SIZE + 1, 0);
  48 }
  49
  50 /*
  51  * ima_appraise_measurement - appraise file measurement
  52  *
  53  * Call evm_verifyxattr() to verify the integrity of 'security.ima'.
  54  * Assuming success, compare the xattr hash with the collected measurement.
  55  *
  56  * Return 0 on success, error code otherwise
  57  */
  58 int ima_appraise_measurement(struct integrity_iint_cache *iint,
  59                              struct file *file, const unsigned char *filename)
  60 {
  61         struct dentry *dentry = file->f_dentry;
  62         struct inode *inode = dentry->d_inode;
  63         u8 xattr_value[IMA_DIGEST_SIZE];
  64         enum integrity_status status = INTEGRITY_UNKNOWN;
  65         const char *op = "appraise_data";
  66         char *cause = "unknown";
  67         int rc;
  68
  69         if (!ima_appraise)
  70                 return 0;
  71         if (!inode->i_op->getxattr)
  72                 return INTEGRITY_UNKNOWN;
  73
  74         if (iint->flags & IMA_APPRAISED)
  75                 return iint->ima_status;
  76
  77         rc = inode->i_op->getxattr(dentry, XATTR_NAME_IMA, xattr_value,
  78                                    IMA_DIGEST_SIZE);
  79         if (rc <= 0) {
  80                 if (rc && rc != -ENODATA)
  81                         goto out;
  82
  83                 cause = "missing-hash";
  84                 status =
  85                     (inode->i_size == 0) ? INTEGRITY_PASS : INTEGRITY_NOLABEL;
  86                 goto out;
  87         }
  88
  89         status = evm_verifyxattr(dentry, XATTR_NAME_IMA, xattr_value, rc, iint);
  90         if ((status != INTEGRITY_PASS) && (status != INTEGRITY_UNKNOWN)) {
  91                 if ((status == INTEGRITY_NOLABEL)
  92                     || (status == INTEGRITY_NOXATTRS))
  93                         cause = "missing-HMAC";
  94                 else if (status == INTEGRITY_FAIL)
  95                         cause = "invalid-HMAC";
  96                 goto out;
  97         }
  98
  99         rc = memcmp(xattr_value, iint->digest, IMA_DIGEST_SIZE);
 100         if (rc) {
 101                 status = INTEGRITY_FAIL;
 102                 cause = "invalid-hash";
 103                 print_hex_dump_bytes("security.ima: ", DUMP_PREFIX_NONE,
 104                                      xattr_value, IMA_DIGEST_SIZE);
 105                 print_hex_dump_bytes("collected: ", DUMP_PREFIX_NONE,
 106                                      iint->digest, IMA_DIGEST_SIZE);
 107                 goto out;
 108         }
 109         status = INTEGRITY_PASS;
 110         iint->flags |= IMA_APPRAISED;
 111 out:
 112         if (status != INTEGRITY_PASS) {
 113                 if (ima_appraise & IMA_APPRAISE_FIX) {
 114                         ima_fix_xattr(dentry, iint);
 115                         status = INTEGRITY_PASS;
 116                 }
 117                 integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode, filename,
 118                                     op, cause, rc, 0);
 119         }
 120         iint->ima_status = status;
 121         return status;
 122 }
 123
 124 /*
 125  * ima_update_xattr - update 'security.ima' hash value
 126  */
 127 void ima_update_xattr(struct integrity_iint_cache *iint, struct file *file)
 128 {
 129         struct dentry *dentry = file->f_dentry;
 130         int rc = 0;
 131
 132         rc = ima_collect_measurement(iint, file);
 133         if (rc < 0)
 134                 return;
 135         ima_fix_xattr(dentry, iint);
 136 }
 137
 138 /**
 139  * ima_inode_post_setattr - reflect file metadata changes
 140  * @dentry: pointer to the affected dentry
 141  *
 142  * Changes to a dentry's metadata might result in needing to appraise.
 143  *
 144  * This function is called from notify_change(), which expects the caller
 145  * to lock the inode's i_mutex.
 146  */
 147 void ima_inode_post_setattr(struct dentry *dentry)
 148 {
 149         struct inode *inode = dentry->d_inode;
 150         struct integrity_iint_cache *iint;
 151         int must_appraise, rc;
 152
 153         if (!ima_initialized || !ima_appraise || !S_ISREG(inode->i_mode)
 154             || !inode->i_op->removexattr)
 155                 return;
 156
 157         must_appraise = ima_must_appraise(inode, MAY_ACCESS, POST_SETATTR);
 158         iint = integrity_iint_find(inode);
 159         if (iint) {
 160                 if (must_appraise)
 161                         iint->flags |= IMA_APPRAISE;
 162                 else
 163                         iint->flags &= ~(IMA_APPRAISE | IMA_APPRAISED);
 164         }
 165         if (!must_appraise)
 166                 rc = inode->i_op->removexattr(dentry, XATTR_NAME_IMA);
 167         return;
 168 }