/**
* BSD Secure Levels LSM
*
* Maintainers:
* Michael A. Halcrow <mike@halcrow.us>
* Serge Hallyn <hallyn@cs.wm.edu>
*
* Copyright (c) 2001 WireX Communications, Inc <chris@wirex.com>
* Copyright (c) 2001 Greg Kroah-Hartman <greg@kroah.com>
* Copyright (c) 2002 International Business Machines <robb@austin.ibm.com>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*/
#include <linux/config.h>
#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/security.h>
#include <linux/netlink.h>
#include <linux/fs.h>
#include <linux/namei.h>
#include <linux/mount.h>
#include <linux/capability.h>
#include <linux/time.h>
#include <linux/proc_fs.h>
#include <linux/kobject.h>
#include <linux/crypto.h>
#include <asm/scatterlist.h>
#include <linux/gfp.h>
#include <linux/sysfs.h>
#define SHA1_DIGEST_SIZE 20
/**
* Module parameter that defines the initial secure level.
*
* When built as a module, it defaults to seclvl 1, which is the
* behavior of BSD secure levels. Note that this default behavior
* wrecks havoc on a machine when the seclvl module is compiled into
* the kernel. In that case, we default to seclvl 0.
*/
#ifdef CONFIG_SECURITY_SECLVL_MODULE
static int initlvl = 1;
#else
static int initlvl;
#endif
module_param(initlvl, int, 0);
MODULE_PARM_DESC(initlvl, "Initial secure level (defaults to 1)");
/* Module parameter that defines the verbosity level */
static int verbosity;
module_param(verbosity, int, 0);
MODULE_PARM_DESC(verbosity, "Initial verbosity level (0 or 1; defaults to "
"0, which is Quiet)");
/**
* Optional password which can be passed in to bring seclvl to 0
* (i.e., for halt/reboot). Defaults to NULL (the passwd attribute
* file will not be registered in sysfs).
*
* This gets converted to its SHA1 hash when stored. It's probably
* not a good idea to use this parameter when loading seclvl from a
* script; use sha1_passwd instead.
*/
#define MAX_PASSWD_SIZE 32
static char passwd[MAX_PASSWD_SIZE];
module_param_string(passwd, passwd, sizeof(passwd), 0);
MODULE_PARM_DESC(passwd,
"Plaintext of password that sets seclvl=0 when written to "
"(sysfs mount point)/seclvl/passwd\n");
/**
* SHA1 hashed version of the optional password which can be passed in
* to bring seclvl to 0 (i.e., for halt/reboot). Must be in
* hexadecimal format (40 characters). Defaults to NULL (the passwd
* attribute file will not be registered in sysfs).
*
* Use the sha1sum utility to generate the SHA1 hash of a password:
*
* echo -n "secret" | sha1sum
*/
#define MAX_SHA1_PASSWD 41
static char sha1_passwd[MAX_SHA1_PASSWD];
module_param_string(sha1_passwd, sha1_passwd, sizeof(sha1_passwd), 0);
MODULE_PARM_DESC(sha1_passwd,
"SHA1 hash (40 hexadecimal characters) of password that "
"sets seclvl=0 when plaintext password is written to "
"(sysfs mount point)/seclvl/passwd\n");
static int hideHash = 1;
module_param(hideHash, int, 0);
MODULE_PARM_DESC(hideHash, "When set to 0, reading seclvl/passwd from sysfs "
"will return the SHA1-hashed value of the password that "
"lowers the secure level to 0.\n");
#define MY_NAME "seclvl"
/**
* This time-limits log writes to one per second.
*/
#define seclvl_printk(verb, type, fmt, arg...) \
do { \
if (verbosity >= verb) { \
static unsigned long _prior; \
unsigned long _now = jiffies; \
if ((_now - _prior) > HZ) { \
printk(type "%s: %s: " fmt, \
MY_NAME, __FUNCTION__ , \
## arg); \
_prior = _now; \
} \
} \
} while (0)
/**
* kobject stuff
*/
struct subsystem seclvl_subsys;
struct seclvl_obj {
char *name;
struct list_head slot_list;
struct kobject kobj;
};
/**
* There is a seclvl_attribute struct for each file in sysfs.
*
* In our case, we have one of these structs for "passwd" and another
* for "seclvl".
*/
struct seclvl_attribute {
struct attribute attr;
ssize_t(*show) (struct seclvl_obj *, char *);
ssize_t(*store) (struct seclvl_obj *, const char *, size_t);
};
/**
* When this function is called, one of the files in sysfs is being
* written to. attribute->store is a function pointer to whatever the
* struct seclvl_attribute store function pointer points to. It is
* unique for "passwd" and "seclvl".
*/
static ssize_t
seclvl_attr_store(struct kobject *kobj,
struct attribute *attr, const char *buf, size_t len)
{
struct seclvl_obj *obj = container_of(kobj, struct seclvl_obj, kobj);
struct seclvl_attribute *attribute =
container_of(attr, struct seclvl_attribute, attr);
return attribute->store ? attribute->store(obj, buf, len) : -EIO;
}
static ssize_t
seclvl_attr_show(struct kobject *kobj, struct attribute *attr, char *buf)
{
struct seclvl_obj *obj = container_of(kobj, struct seclvl_obj, kobj);
struct seclvl_attribute *attribute =
container_of(attr, struct seclvl_attribute, attr);
return attribute->show ? attribute->show(obj, buf) : -EIO;
}
/**
* Callback function pointers for show and store
*/
static struct sysfs_ops seclvlfs_sysfs_ops = {
.show = seclvl_attr_show,
.store = seclvl_attr_store,
};
static struct kobj_type seclvl_ktype = {
.sysfs_ops = &seclvlfs_sysfs_ops
};
decl_subsys(seclvl, &seclvl_ktype, NULL);
/**
* The actual security level. Ranges between -1 and 2 inclusive.
*/
static int seclvl;
/**
* flag to keep track of how we were registered
*/
static int secondary;
/**
* Verifies that the requested secure level is valid, given the current
* secure level.
*/
static int seclvl_sanity(int reqlvl)
{
if ((reqlvl < -1) || (reqlvl > 2)) {
seclvl_printk(1, KERN_WARNING, "Attempt to set seclvl out of "
"range: [%d]\n", reqlvl);
return -EINVAL;
}
if ((seclvl == 0) && (reqlvl == -1))
return 0;
if (reqlvl < seclvl) {
seclvl_printk(1, KERN_WARNING, "Attempt to lower seclvl to "
"[%d]\n", reqlvl);
return -EPERM;
}
return 0;
}
/**
* Called whenever the user reads the sysfs handle to this kernel
* object
*/
static ssize_t seclvl_read_file(struct seclvl_obj *obj, char *buff)
{
return snprintf(buff, PAGE_SIZE, "%d\n", seclvl);
}
/**
* security level advancement rules:
* Valid levels are -1 through 2, inclusive.
* From -1, stuck. [ in case compiled into kernel ]
* From 0 or above, can only increment.
*/
static int do_seclvl_advance(int newlvl)
{
if (newlvl <= seclvl) {
seclvl_printk(1, KERN_WARNING, "Cannot advance to seclvl "
"[%d]\n", newlvl);
return -EINVAL;
}
if (newlvl > 2) {
seclvl_printk(1, KERN_WARNING, "Cannot advance to seclvl "
"[%d]\n", newlvl);
return -EINVAL;
}
if (seclvl == -1) {
seclvl_printk(1, KERN_WARNING, "Not allowed to advance to "
"seclvl [%d]\n", seclvl);
return -EPERM;
}
seclvl = newlvl;
return 0;
}
/**
* Called whenever the user writes to the sysfs handle to this kernel
* object (seclvl/seclvl). It expects a single-digit number.
*/
static ssize_t
seclvl_write_file(struct seclvl_obj *obj, const char *buff, size_t count)
{
unsigned long val;
if (count > 2 || (count == 2 && buff[1] != '\n')) {
seclvl_printk(1, KERN_WARNING, "Invalid value passed to "
"seclvl: [%s]\n", buff);
return -EINVAL;
}
val = buff[0] - 48;
if (seclvl_sanity(val)) {
seclvl_printk(1, KERN_WARNING, "Illegal secure level "
"requested: [%d]\n", (int)val);
return -EPERM;
}
if (do_seclvl_advance(val)) {
seclvl_printk(0, KERN_ERR, "Failure advancing security level "
"to %lu\n", val);
}
return count;
}
/* Generate sysfs_attr_seclvl */
static struct seclvl_attribute sysfs_attr_seclvl =
__ATTR(seclvl, (S_IFREG | S_IRUGO | S_IWUSR), seclvl_read_file,
seclvl_write_file);
static unsigned char hashedPassword[SHA1_DIGEST_SIZE];
/**
* Called whenever the user reads the sysfs passwd handle.
*/
static ssize_t seclvl_read_passwd(struct seclvl_obj *obj, char *buff)
{
/* So just how good *is* your password? :-) */
char tmp[3];
int i = 0;
buff[0] = '\0';
if (hideHash) {
/* Security through obscurity */
return 0;
}
while (i < SHA1_DIGEST_SIZE) {
snprintf(tmp, 3, "%02x", hashedPassword[i]);
strncat(buff, tmp, 2);
i++;
}
strcat(buff, "\n");
return ((SHA1_DIGEST_SIZE * 2) + 1);
}
/**
* Converts a block of plaintext of into its SHA1 hashed value.
*
* It would be nice if crypto had a wrapper to do this for us linear
* people...
*/
static int
plaintext_to_sha1(unsigned char *hash, const char *plaintext, int len)
{
char *pgVirtAddr;
struct crypto_tfm *tfm;
struct scatterlist sg[1];
if (len > PAGE_SIZE) {
seclvl_printk(0, KERN_ERR, "Plaintext password too large (%d "
"characters). Largest possible is %lu "
"bytes.\n", len, PAGE_SIZE);
return -ENOMEM;
}
tfm = crypto_alloc_tfm("sha1", CRYPTO_TFM_REQ_MAY_SLEEP);
if (tfm == NULL) {
seclvl_printk(0, KERN_ERR,
"Failed to load transform for SHA1\n");
return -ENOSYS;
}
// Just get a new page; don't play around with page boundaries
// and scatterlists.
pgVirtAddr = (char *)__get_free_page(GFP_KERNEL);
sg[0].page = virt_to_page(pgVirtAddr);
sg[0].offset = 0;
sg[0].length = len;
strncpy(pgVirtAddr, plaintext, len);
crypto_digest_init(tfm);
crypto_digest_update(tfm, sg, 1);
crypto_digest_final(tfm, hash);
crypto_free_tfm(tfm);
free_page((unsigned long)pgVirtAddr);
return 0;
}
/**
* Called whenever the user writes to the sysfs passwd handle to this kernel
* object. It hashes the password and compares the hashed results.
*/
static ssize_t
seclvl_write_passwd(struct seclvl_obj *obj, const char *buff, size_t count)
{
int i;
unsigned char tmp[SHA1_DIGEST_SIZE];
int rc;
int len;
if (!*passwd && !*sha1_passwd) {
seclvl_printk(0, KERN_ERR, "Attempt to password-unlock the "
"seclvl module, but neither a plain text "
"password nor a SHA1 hashed password was "
"passed in as a module parameter! This is a "
"bug, since it should not be possible to be in "
"this part of the module; please tell a "
"maintainer about this event.\n");
return -EINVAL;
}
len = strlen(buff);
/* ``echo "secret" > seclvl/passwd'' includes a newline */
if (buff[len - 1] == '\n') {
len--;
}
/* Hash the password, then compare the hashed values */
if ((rc = plaintext_to_sha1(tmp, buff, len))) {
seclvl_printk(0, KERN_ERR, "Error hashing password: rc = "
"[%d]\n", rc);
return rc;
}
for (i = 0; i < SHA1_DIGEST_SIZE; i++) {
if (hashedPassword[i] != tmp[i]) {
return -EPERM;
}
}
seclvl_printk(0, KERN_INFO,
"Password accepted; seclvl reduced to 0.\n");
seclvl = 0;
return count;
}
/* Generate sysfs_attr_passwd */
static struct seclvl_attribute sysfs_attr_passwd =
__ATTR(passwd, (S_IFREG | S_IRUGO | S_IWUSR), seclvl_read_passwd,
seclvl_write_passwd);
/**
* Explicitely disallow ptrace'ing the init process.
*/
static int seclvl_ptrace(struct task_struct *parent, struct task_struct *child)
{
if (seclvl >= 0) {
if (child->pid == 1) {
seclvl_printk(1, KERN_WARNING, "Attempt to ptrace "
"the init process dissallowed in "
"secure level %d\n", seclvl);
return -EPERM;
}
}
return 0;
}
/**
* Capability checks for seclvl. The majority of the policy
* enforcement for seclvl takes place here.
*/
static int seclvl_capable(struct task_struct *tsk, int cap)
{
/* init can do anything it wants */
if (tsk->pid == 1)
return 0;
switch (seclvl) {
case 2:
/* fall through */
case 1:
if (cap == CAP_LINUX_IMMUTABLE) {
seclvl_printk(1, KERN_WARNING, "Attempt to modify "
"the IMMUTABLE and/or APPEND extended "
"attribute on a file with the IMMUTABLE "
"and/or APPEND extended attribute set "
"denied in seclvl [%d]\n", seclvl);
return -EPERM;
} else if (cap == CAP_SYS_RAWIO) { // Somewhat broad...
seclvl_printk(1, KERN_WARNING, "Attempt to perform "
"raw I/O while in secure level [%d] "
"denied\n", seclvl);
return -EPERM;
} else if (cap == CAP_NET_ADMIN) {
seclvl_printk(1, KERN_WARNING, "Attempt to perform "
"network administrative task while "
"in secure level [%d] denied\n", seclvl);
return -EPERM;
} else if (cap == CAP_SETUID) {
seclvl_printk(1, KERN_WARNING, "Attempt to setuid "
"while in secure level [%d] denied\n",
seclvl);
return -EPERM;
} else if (cap == CAP_SETGID) {
seclvl_printk(1, KERN_WARNING, "Attempt to setgid "
"while in secure level [%d] denied\n",
seclvl);
} else if (cap == CAP_SYS_MODULE) {
seclvl_printk(1, KERN_WARNING, "Attempt to perform "
"a module operation while in secure "
"level [%d] denied\n", seclvl);
return -EPERM;
}
break;
default:
break;
}
/* from dummy.c */
if (cap_is_fs_cap(cap) ? tsk->fsuid == 0 : tsk->euid == 0)
return 0; /* capability granted */
seclvl_printk(1, KERN_WARNING, "Capability denied\n");
return -EPERM; /* capability denied */
}
/**
* Disallow reversing the clock in seclvl > 1
*/
static int seclvl_settime(struct timespec *tv, struct timezone *tz)
{
struct timespec now;
if (seclvl > 1) {
now = current_kernel_time();
if (tv->tv_sec < now.tv_sec ||
(tv->tv_sec == now.tv_sec && tv->tv_nsec < now.tv_nsec)) {
seclvl_printk(1, KERN_WARNING, "Attempt to decrement "
"time in secure level %d denied: "
"current->pid = [%d], "
"current->group_leader->pid = [%d]\n",
seclvl, current->pid,
current->group_leader->pid);
return -EPERM;
} /* if attempt to decrement time */
} /* if seclvl > 1 */
return 0;
}
/* claim the blockdev to exclude mounters, release on file close */
static int seclvl_bd_claim(struct inode *inode)
{
int holder;
struct block_device *bdev = NULL;
dev_t dev = inode->i_rdev;
bdev = open_by_devnum(dev, FMODE_WRITE);
if (bdev) {
if (bd_claim(bdev, &holder)) {
blkdev_put(bdev);
return -EPERM;
}
/* claimed, mark it to release on close */
inode->i_security = current;
}
return 0;
}
/* release the blockdev if you claimed it */
static void seclvl_bd_release(struct inode *inode)
{
if (inode && S_ISBLK(inode->i_mode) && inode->i_security == current) {
struct block_device *bdev = inode->i_bdev;
if (bdev) {
bd_release(bdev);
blkdev_put(bdev);
inode->i_security = NULL;
}
}
}
/**
* Security for writes to block devices is regulated by this seclvl
* function. Deny all writes to block devices in seclvl 2. In
* seclvl 1, we only deny writes to *mounted* block devices.
*/
static int
seclvl_inode_permission(struct inode *inode, int mask, struct nameidata *nd)
{
if (current->pid != 1 && S_ISBLK(inode->i_mode) && (mask & MAY_WRITE)) {
switch (seclvl) {
case 2:
seclvl_printk(1, KERN_WARNING, "Write to block device "
"denied in secure level [%d]\n", seclvl);
return -EPERM;
case 1:
if (seclvl_bd_claim(inode)) {
seclvl_printk(1, KERN_WARNING,
"Write to mounted block device "
"denied in secure level [%d]\n",
seclvl);
return -EPERM;
}
}
}
return 0;
}
/**
* The SUID and SGID bits cannot be set in seclvl >= 1
*/
static int seclvl_inode_setattr(struct dentry *dentry, struct iattr *iattr)
{
if (seclvl > 0) {
if (iattr->ia_valid & ATTR_MODE)
if (iattr->ia_mode & S_ISUID ||
iattr->ia_mode & S_ISGID) {
seclvl_printk(1, KERN_WARNING, "Attempt to "
"modify SUID or SGID bit "
"denied in seclvl [%d]\n",
seclvl);
return -EPERM;
}
}
return 0;
}
/* release busied block devices */
static void seclvl_file_free_security(struct file *filp)
{
struct dentry *dentry = filp->f_dentry;
struct inode *inode = NULL;
if (dentry) {
inode = dentry->d_inode;
seclvl_bd_release(inode);
}
}
/**
* Cannot unmount in secure level 2
*/
static int seclvl_umount(struct vfsmount *mnt, int flags)
{
if (current->pid == 1) {
return 0;
}
if (seclvl == 2) {
seclvl_printk(1, KERN_WARNING, "Attempt to unmount in secure "
"level %d\n", seclvl);
return -EPERM;
}
return 0;
}
static struct security_operations seclvl_ops = {
.ptrace = seclvl_ptrace,
.capable = seclvl_capable,
.inode_permission = seclvl_inode_permission,
.inode_setattr = seclvl_inode_setattr,
.file_free_security = seclvl_file_free_security,
.settime = seclvl_settime,
.sb_umount = seclvl_umount,
};
/**
* Process the password-related module parameters
*/
static int processPassword(void)
{
int rc = 0;
hashedPassword[0] = '\0';
if (*passwd) {
if (*sha1_passwd) {
seclvl_printk(0, KERN_ERR, "Error: Both "
"passwd and sha1_passwd "
"were set, but they are mutually "
"exclusive.\n");
return -EINVAL;
}
if ((rc = plaintext_to_sha1(hashedPassword, passwd,
strlen(passwd)))) {
seclvl_printk(0, KERN_ERR, "Error: SHA1 support not "
"in kernel\n");
return rc;
}
/* All static data goes to the BSS, which zero's the
* plaintext password out for us. */
} else if (*sha1_passwd) { // Base 16
int i;
i = strlen(sha1_passwd);
if (i != (SHA1_DIGEST_SIZE * 2)) {
seclvl_printk(0, KERN_ERR, "Received [%d] bytes; "
"expected [%d] for the hexadecimal "
"representation of the SHA1 hash of "
"the password.\n",
i, (SHA1_DIGEST_SIZE * 2));
return -EINVAL;
}
while ((i -= 2) + 2) {
unsigned char tmp;
tmp = sha1_passwd[i + 2];
sha1_passwd[i + 2] = '\0';
hashedPassword[i / 2] = (unsigned char)
simple_strtol(&sha1_passwd[i], NULL, 16);
sha1_passwd[i + 2] = tmp;
}
}
return 0;
}
/**
* Sysfs registrations
*/
static int doSysfsRegistrations(void)
{
int rc = 0;
if ((rc = subsystem_register(&seclvl_subsys))) {
seclvl_printk(0, KERN_WARNING,
"Error [%d] registering seclvl subsystem\n", rc);
return rc;
}
sysfs_create_file(&seclvl_subsys.kset.kobj, &sysfs_attr_seclvl.attr);
if (*passwd || *sha1_passwd) {
sysfs_create_file(&seclvl_subsys.kset.kobj,
&sysfs_attr_passwd.attr);
}
return 0;
}
/**
* Initialize the seclvl module.
*/
static int __init seclvl_init(void)
{
int rc = 0;
if (verbosity < 0 || verbosity > 1) {
printk(KERN_ERR "Error: bad verbosity [%d]; only 0 or 1 "
"are valid values\n", verbosity);
rc = -EINVAL;
goto exit;
}
sysfs_attr_seclvl.attr.owner = THIS_MODULE;
sysfs_attr_passwd.attr.owner = THIS_MODULE;
if (initlvl < -1 || initlvl > 2) {
seclvl_printk(0, KERN_ERR, "Error: bad initial securelevel "
"[%d].\n", initlvl);
rc = -EINVAL;
goto exit;
}
seclvl = initlvl;
if ((rc = processPassword())) {
seclvl_printk(0, KERN_ERR, "Error processing the password "
"module parameter(s): rc = [%d]\n", rc);
goto exit;
}
/* register ourselves with the security framework */
if (register_security(&seclvl_ops)) {
seclvl_printk(0, KERN_ERR,
"seclvl: Failure registering with the "
"kernel.\n");
/* try registering with primary module */
rc = mod_reg_security(MY_NAME, &seclvl_ops);
if (rc) {
seclvl_printk(0, KERN_ERR, "seclvl: Failure "
"registering with primary security "
"module.\n");
goto exit;
} /* if primary module registered */
secondary = 1;
} /* if we registered ourselves with the security framework */
if ((rc = doSysfsRegistrations())) {
seclvl_printk(0, KERN_ERR, "Error registering with sysfs\n");
goto exit;
}
seclvl_printk(0, KERN_INFO, "seclvl: Successfully initialized.\n");
exit:
if (rc) {
printk(KERN_ERR "seclvl: Error during initialization: rc = "
"[%d]\n", rc);
}
return rc;
}
/**
* Remove the seclvl module.
*/
static void __exit seclvl_exit(void)
{
sysfs_remove_file(&seclvl_subsys.kset.kobj, &sysfs_attr_seclvl.attr);
if (*passwd || *sha1_passwd) {
sysfs_remove_file(&seclvl_subsys.kset.kobj,
&sysfs_attr_passwd.attr);
}
subsystem_unregister(&seclvl_subsys);
if (secondary == 1) {
mod_unreg_security(MY_NAME, &seclvl_ops);
} else if (unregister_security(&seclvl_ops)) {
seclvl_printk(0, KERN_INFO,
"seclvl: Failure unregistering with the "
"kernel\n");
}
}
module_init(seclvl_init);
module_exit(seclvl_exit);
MODULE_AUTHOR("Michael A. Halcrow <mike@halcrow.us>");
MODULE_DESCRIPTION("LSM implementation of the BSD Secure Levels");
MODULE_LICENSE("GPL");
