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* Plan 9 style capability device implementation for the Linux Kernel
*
* Copyright 2008, 2009 Ashwin Ganti <ashwin.ganti@gmail.com>
*
* Released under the GPLv2
*
*/
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/moduleparam.h>
#include <linux/slab.h>
#include <linux/fs.h>
#include <linux/errno.h>
#include <linux/fcntl.h>
#include <linux/cdev.h>
#include <linux/uaccess.h>
#include <linux/list.h>
#include <linux/mm.h>
#include <linux/string.h>
#include <linux/crypto.h>
#include <linux/highmem.h>
#include <linux/scatterlist.h>
#include <linux/sched.h>
#include <linux/cred.h>
#ifndef CAP_MAJOR
#define CAP_MAJOR 0
#endif
#ifndef CAP_NR_DEVS
#define CAP_NR_DEVS 2 /* caphash and capuse */
#endif
#ifndef CAP_NODE_SIZE
#define CAP_NODE_SIZE 20
#endif
#define MAX_DIGEST_SIZE 20
struct cap_node {
char data[CAP_NODE_SIZE];
struct list_head list;
};
struct cap_dev {
struct cap_node *head;
int node_size;
unsigned long size;
struct semaphore sem;
struct cdev cdev;
};
static int cap_major = CAP_MAJOR;
static int cap_minor;
static int cap_nr_devs = CAP_NR_DEVS;
static int cap_node_size = CAP_NODE_SIZE;
module_param(cap_major, int, S_IRUGO);
module_param(cap_minor, int, S_IRUGO);
module_param(cap_nr_devs, int, S_IRUGO);
MODULE_AUTHOR("Ashwin Ganti");
MODULE_LICENSE("GPL");
static struct cap_dev *cap_devices;
static void hexdump(unsigned char *buf, unsigned int len)
{
while (len--)
printk("%02x", *buf++);
printk("\n");
}
static char *cap_hash(char *plain_text, unsigned int plain_text_size,
char *key, unsigned int key_size)
{
struct scatterlist sg;
char *result;
struct crypto_hash *tfm;
struct hash_desc desc;
int ret;
tfm = crypto_alloc_hash("hmac(sha1)", 0, CRYPTO_ALG_ASYNC);
if (IS_ERR(tfm)) {
printk(KERN_ERR
"failed to load transform for hmac(sha1): %ld\n",
PTR_ERR(tfm));
return NULL;
}
desc.tfm = tfm;
desc.flags = 0;
result = kzalloc(MAX_DIGEST_SIZE, GFP_KERNEL);
if (!result) {
printk(KERN_ERR "out of memory!\n");
goto out;
}
sg_set_buf(&sg, plain_text, plain_text_size);
ret = crypto_hash_setkey(tfm, key, key_size);
if (ret) {
printk(KERN_ERR "setkey() failed ret=%d\n", ret);
kfree(result);
result = NULL;
goto out;
}
ret = crypto_hash_digest(&desc, &sg, plain_text_size, result);
if (ret) {
printk(KERN_ERR "digest () failed ret=%d\n", ret);
kfree(result);
result = NULL;
goto out;
}
printk(KERN_DEBUG "crypto hash digest size %d\n",
crypto_hash_digestsize(tfm));
hexdump(result, MAX_DIGEST_SIZE);
out:
crypto_free_hash(tfm);
return result;
}
static int cap_trim(struct cap_dev *dev)
{
struct cap_node *tmp;
struct list_head *pos, *q;
if (dev->head != NULL) {
list_for_each_safe(pos, q, &(dev->head->list)) {
tmp = list_entry(pos, struct cap_node, list);
list_del(pos);
kfree(tmp);
}
}
return 0;
}
static int cap_open(struct inode *inode, struct file *filp)
{
struct cap_dev *dev;
dev = container_of(inode->i_cdev, struct cap_dev, cdev);
filp->private_data = dev;
/* trim to 0 the length of the device if open was write-only */
if ((filp->f_flags & O_ACCMODE) == O_WRONLY) {
if (down_interruptible(&dev->sem))
return -ERESTARTSYS;
cap_trim(dev);
up(&dev->sem);
}
/* initialise the head if it is NULL */
if (dev->head == NULL) {
dev->head = kmalloc(sizeof(struct cap_node), GFP_KERNEL);
INIT_LIST_HEAD(&(dev->head->list));
}
return 0;
}
static int cap_release(struct inode *inode, struct file *filp)
{
return 0;
}
static ssize_t cap_write(struct file *filp, const char __user *buf,
size_t count, loff_t *f_pos)
{
struct cap_node *node_ptr, *tmp;
struct list_head *pos;
struct cap_dev *dev = filp->private_data;
ssize_t retval = -ENOMEM;
struct cred *new;
int len, target_int, source_int, flag = 0;
char *user_buf, *user_buf_running, *source_user, *target_user,
*rand_str, *hash_str, *result;
if (down_interruptible(&dev->sem))
return -ERESTARTSYS;
user_buf_running = NULL;
hash_str = NULL;
node_ptr = kmalloc(sizeof(struct cap_node), GFP_KERNEL);
user_buf = kzalloc(count+1, GFP_KERNEL);
if (!node_ptr || !user_buf)
goto out;
if (copy_from_user(user_buf, buf, count)) {
retval = -EFAULT;
goto out;
}
/*
* If the minor number is 0 ( /dev/caphash ) then simply add the
* hashed capability supplied by the user to the list of hashes
*/
if (0 == iminor(filp->f_dentry->d_inode)) {
if (count > CAP_NODE_SIZE) {
retval = -EINVAL;
goto out;
}
printk(KERN_INFO "Capability being written to /dev/caphash : \n");
hexdump(user_buf, count);
memcpy(node_ptr->data, user_buf, count);
list_add(&(node_ptr->list), &(dev->head->list));
node_ptr = NULL;
} else {
char *tmpu;
if (!cap_devices[0].head ||
list_empty(&(cap_devices[0].head->list))) {
retval = -EINVAL;
goto out;
}
/*
* break the supplied string into tokens with @ as the
* delimiter If the string is "user1@user2@randomstring" we
* need to split it and hash 'user1@user2' using 'randomstring'
* as the key.
*/
tmpu = user_buf_running = kstrdup(user_buf, GFP_KERNEL);
source_user = strsep(&tmpu, "@");
target_user = strsep(&tmpu, "@");
rand_str = tmpu;
if (!source_user || !target_user || !rand_str) {
retval = -EINVAL;
goto out;
}
/* hash the string user1@user2 with rand_str as the key */
len = strlen(source_user) + strlen(target_user) + 1;
/* src, @, len, \0 */
hash_str = kzalloc(len+1, GFP_KERNEL);
strcat(hash_str, source_user);
strcat(hash_str, "@");
strcat(hash_str, target_user);
printk(KERN_ALERT "the source user is %s \n", source_user);
printk(KERN_ALERT "the target user is %s \n", target_user);
result = cap_hash(hash_str, len, rand_str, strlen(rand_str));
if (NULL == result) {
retval = -EFAULT;
goto out;
}
memcpy(node_ptr->data, result, CAP_NODE_SIZE); /* why? */
/* Change the process's uid if the hash is present in the
* list of hashes
*/
list_for_each(pos, &(cap_devices->head->list)) {
/*
* Change the user id of the process if the hashes
* match
*/
if (0 ==
memcmp(result,
list_entry(pos, struct cap_node,
list)->data,
CAP_NODE_SIZE)) {
target_int = (unsigned int)
simple_strtol(target_user, NULL, 0);
source_int = (unsigned int)
simple_strtol(source_user, NULL, 0);
flag = 1;
/*
* Check whether the process writing to capuse
* is actually owned by the source owner
*/
if (source_int != current_uid()) {
printk(KERN_ALERT
"Process is not owned by the source user of the capability.\n");
retval = -EFAULT;
goto out;
}
/*
* What all id's need to be changed here? uid,
* euid, fsid, savedids ?? Currently I am
* changing the effective user id since most of
* the authorisation decisions are based on it
*/
new = prepare_creds();
if (!new) {
retval = -ENOMEM;
goto out;
}
new->uid = (uid_t) target_int;
new->euid = (uid_t) target_int;
retval = commit_creds(new);
if (retval)
goto out;
/*
* Remove the capability from the list and
* break
*/
tmp = list_entry(pos, struct cap_node, list);
list_del(pos);
kfree(tmp);
break;
}
}
if (0 == flag) {
/*
* The capability is not present in the list of the
* hashes stored, hence return failure
*/
printk(KERN_ALERT
"Invalid capabiliy written to /dev/capuse \n");
retval = -EFAULT;
goto out;
}
}
*f_pos += count;
retval = count;
/* update the size */
if (dev->size < *f_pos)
dev->size = *f_pos;
out:
kfree(node_ptr);
kfree(user_buf);
kfree(user_buf_running);
kfree(hash_str);
up(&dev->sem);
return retval;
}
static const struct file_operations cap_fops = {
.owner = THIS_MODULE,
.write = cap_write,
.open = cap_open,
.release = cap_release,
};
/* no __exit here because it can be called by the init function */
static void cap_cleanup_module(void)
{
int i;
dev_t devno = MKDEV(cap_major, cap_minor);
if (cap_devices) {
for (i = 0; i < cap_nr_devs; i++) {
cap_trim(cap_devices + i);
cdev_del(&cap_devices[i].cdev);
}
kfree(cap_devices);
}
unregister_chrdev_region(devno, cap_nr_devs);
}
static void cap_setup_cdev(struct cap_dev *dev, int index)
{
int err, devno = MKDEV(cap_major, cap_minor + index);
cdev_init(&dev->cdev, &cap_fops);
dev->cdev.owner = THIS_MODULE;
dev->cdev.ops = &cap_fops;
err = cdev_add(&dev->cdev, devno, 1);
if (err)
printk(KERN_NOTICE "Error %d adding cap%d", err, index);
}
static int __init cap_init_module(void)
{
int result, i;
dev_t dev = 0;
if (cap_major) {
dev = MKDEV(cap_major, cap_minor);
result = register_chrdev_region(dev, cap_nr_devs, "cap");
} else {
result = alloc_chrdev_region(&dev, cap_minor, cap_nr_devs,
"cap");
cap_major = MAJOR(dev);
}
if (result < 0) {
printk(KERN_WARNING "cap: can't get major %d\n",
cap_major);
return result;
}
cap_devices = kzalloc(cap_nr_devs * sizeof(struct cap_dev),
GFP_KERNEL);
if (!cap_devices) {
result = -ENOMEM;
goto fail;
}
/* Initialize each device. */
for (i = 0; i < cap_nr_devs; i++) {
cap_devices[i].node_size = cap_node_size;
init_MUTEX(&cap_devices[i].sem);
cap_setup_cdev(&cap_devices[i], i);
}
return 0;
fail:
cap_cleanup_module();
return result;
}
module_init(cap_init_module);
module_exit(cap_cleanup_module);
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