security/integrity/evm/evm_secfs.c

   1 /*
   2  * Copyright (C) 2010 IBM Corporation
   3  *
   4  * Authors:
   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  * File: evm_secfs.c
  12  *      - Used to signal when key is on keyring
  13  *      - Get the key and enable EVM
  14  */
  15
  16 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  17
  18 #include <linux/uaccess.h>
  19 #include <linux/module.h>
  20 #include "evm.h"
  21
  22 static struct dentry *evm_init_tpm;
  23
  24 /**
  25  * evm_read_key - read() for <securityfs>/evm
  26  *
  27  * @filp: file pointer, not actually used
  28  * @buf: where to put the result
  29  * @count: maximum to send along
  30  * @ppos: where to start
  31  *
  32  * Returns number of bytes read or error code, as appropriate
  33  */
  34 static ssize_t evm_read_key(struct file *filp, char __user *buf,
  35                             size_t count, loff_t *ppos)
  36 {
  37         char temp[80];
  38         ssize_t rc;
  39
  40         if (*ppos != 0)
  41                 return 0;
  42
  43         sprintf(temp, "%d", (evm_initialized & ~EVM_SETUP_COMPLETE));
  44         rc = simple_read_from_buffer(buf, count, ppos, temp, strlen(temp));
  45
  46         return rc;
  47 }
  48
  49 /**
  50  * evm_write_key - write() for <securityfs>/evm
  51  * @file: file pointer, not actually used
  52  * @buf: where to get the data from
  53  * @count: bytes sent
  54  * @ppos: where to start
  55  *
  56  * Used to signal that key is on the kernel key ring.
  57  * - get the integrity hmac key from the kernel key ring
  58  * - create list of hmac protected extended attributes
  59  * Returns number of bytes written or error code, as appropriate
  60  */
  61 static ssize_t evm_write_key(struct file *file, const char __user *buf,
  62                              size_t count, loff_t *ppos)
  63 {
  64         int i, ret;
  65
  66         if (!capable(CAP_SYS_ADMIN) || (evm_initialized & EVM_SETUP_COMPLETE))
  67                 return -EPERM;
  68
  69         ret = kstrtoint_from_user(buf, count, 0, &i);
  70
  71         if (ret)
  72                 return ret;
  73
  74         /* Reject invalid values */
  75         if (!i || (i & ~EVM_INIT_MASK) != 0)
  76                 return -EINVAL;
  77
  78         /* Don't allow a request to freshly enable metadata writes if
  79          * keys are loaded.
  80          */
  81         if ((i & EVM_ALLOW_METADATA_WRITES) &&
  82             ((evm_initialized & EVM_KEY_MASK) != 0) &&
  83             !(evm_initialized & EVM_ALLOW_METADATA_WRITES))
  84                 return -EPERM;
  85
  86         if (i & EVM_INIT_HMAC) {
  87                 ret = evm_init_key();
  88                 if (ret != 0)
  89                         return ret;
  90                 /* Forbid further writes after the symmetric key is loaded */
  91                 i |= EVM_SETUP_COMPLETE;
  92         }
  93
  94         evm_initialized |= i;
  95
  96         /* Don't allow protected metadata modification if a symmetric key
  97          * is loaded
  98          */
  99         if (evm_initialized & EVM_INIT_HMAC)
 100                 evm_initialized &= ~(EVM_ALLOW_METADATA_WRITES);
 101
 102         return count;
 103 }
 104
 105 static const struct file_operations evm_key_ops = {
 106         .read           = evm_read_key,
 107         .write          = evm_write_key,
 108 };
 109
 110 int __init evm_init_secfs(void)
 111 {
 112         int error = 0;
 113
 114         evm_init_tpm = securityfs_create_file("evm", S_IRUSR | S_IRGRP,
 115                                               NULL, NULL, &evm_key_ops);
 116         if (!evm_init_tpm || IS_ERR(evm_init_tpm))
 117                 error = -EFAULT;
 118         return error;
 119 }