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));
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))
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 	if (i & EVM_INIT_HMAC) {
79 		ret = evm_init_key();
80 		if (ret != 0)
81 			return ret;
82 		/* Forbid further writes after the symmetric key is loaded */
83 		i |= EVM_SETUP;
84 	}
85 
86 	evm_initialized |= i;
87 
88 	return count;
89 }
90 
91 static const struct file_operations evm_key_ops = {
92 	.read		= evm_read_key,
93 	.write		= evm_write_key,
94 };
95 
96 int __init evm_init_secfs(void)
97 {
98 	int error = 0;
99 
100 	evm_init_tpm = securityfs_create_file("evm", S_IRUSR | S_IRGRP,
101 					      NULL, NULL, &evm_key_ops);
102 	if (!evm_init_tpm || IS_ERR(evm_init_tpm))
103 		error = -EFAULT;
104 	return error;
105 }
106