Ashwin Ganti | 5564317 | 2009-02-24 19:48:44 -0800 | [diff] [blame] | 1 | /* |
| 2 | * Plan 9 style capability device implementation for the Linux Kernel |
| 3 | * |
| 4 | * Copyright 2008, 2009 Ashwin Ganti <ashwin.ganti@gmail.com> |
| 5 | * |
| 6 | * Released under the GPLv2 |
| 7 | * |
| 8 | */ |
| 9 | #include <linux/module.h> |
| 10 | #include <linux/moduleparam.h> |
| 11 | #include <linux/init.h> |
| 12 | #include <linux/kernel.h> |
| 13 | #include <linux/slab.h> |
| 14 | #include <linux/fs.h> |
| 15 | #include <linux/errno.h> |
| 16 | #include <linux/types.h> |
| 17 | #include <linux/proc_fs.h> |
| 18 | #include <linux/fcntl.h> |
| 19 | #include <linux/cdev.h> |
| 20 | #include <linux/syscalls.h> |
| 21 | #include <asm/system.h> |
| 22 | #include <asm/uaccess.h> |
| 23 | #include <linux/list.h> |
| 24 | #include <linux/err.h> |
| 25 | #include <linux/mm.h> |
| 26 | #include <linux/string.h> |
| 27 | #include <linux/crypto.h> |
| 28 | #include <linux/highmem.h> |
| 29 | #include <linux/jiffies.h> |
| 30 | #include <linux/timex.h> |
| 31 | #include <linux/interrupt.h> |
| 32 | #include <linux/scatterlist.h> |
| 33 | #include <linux/crypto.h> |
Greg Kroah-Hartman | 5dba082 | 2009-02-24 20:06:34 -0800 | [diff] [blame] | 34 | #include <linux/sched.h> |
| 35 | #include <linux/cred.h> |
Greg Kroah-Hartman | 4bf0438 | 2009-02-24 20:11:39 -0800 | [diff] [blame^] | 36 | |
| 37 | #ifndef CAP_MAJOR |
| 38 | #define CAP_MAJOR 0 |
| 39 | #endif |
| 40 | |
| 41 | #ifndef CAP_NR_DEVS |
| 42 | #define CAP_NR_DEVS 2 /* caphash and capuse */ |
| 43 | #endif |
| 44 | |
| 45 | #ifndef CAP_NODE_SIZE |
| 46 | #define CAP_NODE_SIZE 20 |
| 47 | #endif |
| 48 | |
| 49 | #define MAX_DIGEST_SIZE 20 |
| 50 | |
| 51 | struct cap_node { |
| 52 | char data[CAP_NODE_SIZE]; |
| 53 | struct list_head list; |
| 54 | }; |
| 55 | |
| 56 | struct cap_dev { |
| 57 | struct cap_node *head; |
| 58 | int node_size; |
| 59 | unsigned long size; |
| 60 | struct semaphore sem; |
| 61 | struct cdev cdev; |
| 62 | }; |
| 63 | |
| 64 | int cap_trim(struct cap_dev *); |
| 65 | ssize_t cap_write(struct file *, const char __user *, size_t, loff_t *); |
| 66 | char *cap_hash(char *plain_text, unsigned int plain_text_size, char *key, unsigned int key_size); |
| 67 | void hex_dump(unsigned char * buf, unsigned int len); |
Ashwin Ganti | 5564317 | 2009-02-24 19:48:44 -0800 | [diff] [blame] | 68 | |
| 69 | int cap_major = CAP_MAJOR; |
| 70 | int cap_minor = 0; |
| 71 | int cap_nr_devs = CAP_NR_DEVS; |
| 72 | int cap_node_size = CAP_NODE_SIZE; |
| 73 | |
| 74 | module_param(cap_major, int, S_IRUGO); |
| 75 | module_param(cap_minor, int, S_IRUGO); |
| 76 | module_param(cap_nr_devs, int, S_IRUGO); |
| 77 | |
| 78 | MODULE_AUTHOR("Ashwin Ganti"); |
| 79 | MODULE_LICENSE("GPL"); |
| 80 | |
| 81 | struct cap_dev *cap_devices; |
| 82 | |
| 83 | void hexdump(unsigned char *buf, unsigned int len) |
| 84 | { |
| 85 | while (len--) |
| 86 | printk("%02x", *buf++); |
| 87 | printk("\n"); |
| 88 | } |
| 89 | |
| 90 | int cap_trim(struct cap_dev *dev) |
| 91 | { |
| 92 | struct cap_node *tmp; |
| 93 | struct list_head *pos, *q; |
| 94 | if (dev->head != NULL) { |
| 95 | list_for_each_safe(pos, q, &(dev->head->list)) { |
| 96 | tmp = list_entry(pos, struct cap_node, list); |
| 97 | list_del(pos); |
| 98 | kfree(tmp); |
| 99 | } |
| 100 | } |
| 101 | return 0; |
| 102 | } |
| 103 | |
| 104 | int cap_open(struct inode *inode, struct file *filp) |
| 105 | { |
| 106 | struct cap_dev *dev; |
| 107 | dev = container_of(inode->i_cdev, struct cap_dev, cdev); |
| 108 | filp->private_data = dev; |
| 109 | |
| 110 | /* trim to 0 the length of the device if open was write-only */ |
| 111 | if ((filp->f_flags & O_ACCMODE) == O_WRONLY) { |
| 112 | if (down_interruptible(&dev->sem)) |
| 113 | return -ERESTARTSYS; |
| 114 | cap_trim(dev); |
| 115 | up(&dev->sem); |
| 116 | } |
| 117 | /* initialise the head if it is NULL */ |
| 118 | if (dev->head == NULL) { |
| 119 | dev->head = |
| 120 | (struct cap_node *) kmalloc(sizeof(struct cap_node), |
| 121 | GFP_KERNEL); |
| 122 | INIT_LIST_HEAD(&(dev->head->list)); |
| 123 | } |
| 124 | return 0; |
| 125 | } |
| 126 | |
| 127 | int cap_release(struct inode *inode, struct file *filp) |
| 128 | { |
| 129 | return 0; |
| 130 | } |
| 131 | |
| 132 | ssize_t |
| 133 | cap_write(struct file * filp, const char __user * buf, |
| 134 | size_t count, loff_t * f_pos) |
| 135 | { |
| 136 | struct cap_node *node_ptr, *tmp; |
| 137 | struct list_head *pos; |
| 138 | struct cap_dev *dev = filp->private_data; |
| 139 | ssize_t retval = -ENOMEM; |
Greg Kroah-Hartman | 5dba082 | 2009-02-24 20:06:34 -0800 | [diff] [blame] | 140 | struct cred *new; |
Ashwin Ganti | 5564317 | 2009-02-24 19:48:44 -0800 | [diff] [blame] | 141 | int len, target_int, source_int, flag = 0; |
| 142 | char *user_buf, *user_buf_running, *source_user, *target_user, |
| 143 | *rand_str, *hash_str, *result; |
| 144 | |
| 145 | if (down_interruptible(&dev->sem)) |
| 146 | return -ERESTARTSYS; |
| 147 | |
| 148 | node_ptr = |
| 149 | (struct cap_node *) kmalloc(sizeof(struct cap_node), |
| 150 | GFP_KERNEL); |
| 151 | user_buf = (char *) kmalloc(count, GFP_KERNEL); |
| 152 | memset(user_buf, 0, count); |
| 153 | |
| 154 | if (copy_from_user(user_buf, buf, count)) { |
| 155 | retval = -EFAULT; |
| 156 | goto out; |
| 157 | } |
| 158 | |
| 159 | /* If the minor number is 0 ( /dev/caphash ) then simply add the |
| 160 | * hashed capability supplied by the user to the list of hashes |
| 161 | */ |
| 162 | if (0 == iminor(filp->f_dentry->d_inode)) { |
| 163 | printk(KERN_INFO "Capability being written to /dev/caphash : \n"); |
| 164 | hexdump(user_buf, count); |
| 165 | memcpy(node_ptr->data, user_buf, count); |
| 166 | list_add(&(node_ptr->list), &(dev->head->list)); |
| 167 | } else { |
| 168 | /* break the supplied string into tokens with @ as the delimiter |
| 169 | If the string is "user1@user2@randomstring" we need to split it |
| 170 | and hash 'user1@user2' using 'randomstring' as the key |
| 171 | */ |
| 172 | user_buf_running = kstrdup(user_buf, GFP_KERNEL); |
| 173 | source_user = strsep(&user_buf_running, "@"); |
| 174 | target_user = strsep(&user_buf_running, "@"); |
| 175 | rand_str = strsep(&user_buf_running, "@"); |
| 176 | |
| 177 | /* hash the string user1@user2 with rand_str as the key */ |
| 178 | len = strlen(source_user) + strlen(target_user) + 1; |
| 179 | hash_str = (char *) kmalloc(len, GFP_KERNEL); |
| 180 | memset(hash_str, 0, len); |
| 181 | strcat(hash_str, source_user); |
| 182 | strcat(hash_str, "@"); |
| 183 | strcat(hash_str, target_user); |
| 184 | |
| 185 | printk(KERN_ALERT "the source user is %s \n", source_user); |
| 186 | printk(KERN_ALERT "the target user is %s \n", target_user); |
| 187 | |
| 188 | result = |
| 189 | cap_hash(hash_str, len, rand_str, strlen(rand_str)); |
| 190 | if (NULL == result) { |
| 191 | retval = -EFAULT; |
| 192 | goto out; |
| 193 | } |
| 194 | memcpy(node_ptr->data, result, CAP_NODE_SIZE); |
| 195 | /* Change the process's uid if the hash is present in the |
| 196 | * list of hashes |
| 197 | */ |
| 198 | list_for_each(pos, &(cap_devices->head->list)) { |
| 199 | /* Change the user id of the process if the hashes match */ |
| 200 | if (0 == |
| 201 | memcmp(result, |
| 202 | list_entry(pos, struct cap_node, |
| 203 | list)->data, |
| 204 | CAP_NODE_SIZE)) { |
| 205 | target_int = (unsigned int) |
| 206 | simple_strtol(target_user, NULL, 0); |
| 207 | source_int = (unsigned int) |
| 208 | simple_strtol(source_user, NULL, 0); |
| 209 | flag = 1; |
| 210 | |
| 211 | /* Check whether the process writing to capuse is actually owned by |
| 212 | * the source owner |
| 213 | */ |
Greg Kroah-Hartman | 5dba082 | 2009-02-24 20:06:34 -0800 | [diff] [blame] | 214 | if (source_int != current_uid()) { |
Ashwin Ganti | 5564317 | 2009-02-24 19:48:44 -0800 | [diff] [blame] | 215 | printk(KERN_ALERT |
| 216 | "Process is not owned by the source user of the capability.\n"); |
| 217 | retval = -EFAULT; |
| 218 | goto out; |
| 219 | } |
| 220 | /* What all id's need to be changed here? uid, euid, fsid, savedids ?? |
| 221 | * Currently I am changing the effective user id |
| 222 | * since most of the authorisation decisions are based on it |
| 223 | */ |
Greg Kroah-Hartman | 5dba082 | 2009-02-24 20:06:34 -0800 | [diff] [blame] | 224 | new = prepare_creds(); |
| 225 | if (!new) { |
| 226 | retval = -ENOMEM; |
| 227 | goto out; |
| 228 | } |
| 229 | new->uid = (uid_t) target_int; |
| 230 | new->euid = (uid_t) target_int; |
| 231 | retval = commit_creds(new); |
| 232 | if (retval) |
| 233 | goto out; |
Ashwin Ganti | 5564317 | 2009-02-24 19:48:44 -0800 | [diff] [blame] | 234 | |
| 235 | /* Remove the capability from the list and break */ |
| 236 | tmp = |
| 237 | list_entry(pos, struct cap_node, list); |
| 238 | list_del(pos); |
| 239 | kfree(tmp); |
| 240 | break; |
| 241 | } |
| 242 | } |
| 243 | if (0 == flag) { |
| 244 | /* The capability is not present in the list of the hashes stored, hence return failure */ |
| 245 | printk(KERN_ALERT |
| 246 | "Invalid capabiliy written to /dev/capuse \n"); |
| 247 | retval = -EFAULT; |
| 248 | goto out; |
| 249 | } |
| 250 | } |
| 251 | *f_pos += count; |
| 252 | retval = count; |
| 253 | /* update the size */ |
| 254 | if (dev->size < *f_pos) |
| 255 | dev->size = *f_pos; |
| 256 | |
| 257 | out: |
| 258 | up(&dev->sem); |
| 259 | return retval; |
| 260 | } |
| 261 | |
| 262 | struct file_operations cap_fops = { |
| 263 | .owner = THIS_MODULE, |
| 264 | .write = cap_write, |
| 265 | .open = cap_open, |
| 266 | .release = cap_release, |
| 267 | }; |
| 268 | |
| 269 | |
| 270 | void cap_cleanup_module(void) |
| 271 | { |
| 272 | int i; |
| 273 | dev_t devno = MKDEV(cap_major, cap_minor); |
| 274 | if (cap_devices) { |
| 275 | for (i = 0; i < cap_nr_devs; i++) { |
| 276 | cap_trim(cap_devices + i); |
| 277 | cdev_del(&cap_devices[i].cdev); |
| 278 | } |
| 279 | kfree(cap_devices); |
| 280 | } |
| 281 | unregister_chrdev_region(devno, cap_nr_devs); |
| 282 | |
| 283 | } |
| 284 | |
| 285 | |
| 286 | static void cap_setup_cdev(struct cap_dev *dev, int index) |
| 287 | { |
| 288 | int err, devno = MKDEV(cap_major, cap_minor + index); |
| 289 | cdev_init(&dev->cdev, &cap_fops); |
| 290 | dev->cdev.owner = THIS_MODULE; |
| 291 | dev->cdev.ops = &cap_fops; |
| 292 | err = cdev_add(&dev->cdev, devno, 1); |
| 293 | if (err) |
| 294 | printk(KERN_NOTICE "Error %d adding cap%d", err, index); |
| 295 | } |
| 296 | |
| 297 | |
| 298 | int cap_init_module(void) |
| 299 | { |
| 300 | int result, i; |
| 301 | dev_t dev = 0; |
| 302 | |
| 303 | if (cap_major) { |
| 304 | dev = MKDEV(cap_major, cap_minor); |
| 305 | result = register_chrdev_region(dev, cap_nr_devs, "cap"); |
| 306 | } else { |
| 307 | result = alloc_chrdev_region(&dev, cap_minor, cap_nr_devs, |
| 308 | "cap"); |
| 309 | cap_major = MAJOR(dev); |
| 310 | } |
| 311 | |
| 312 | if (result < 0) { |
| 313 | printk(KERN_WARNING "cap: can't get major %d\n", |
| 314 | cap_major); |
| 315 | return result; |
| 316 | } |
| 317 | |
| 318 | cap_devices = |
| 319 | kmalloc(cap_nr_devs * sizeof(struct cap_dev), GFP_KERNEL); |
| 320 | if (!cap_devices) { |
| 321 | result = -ENOMEM; |
| 322 | goto fail; |
| 323 | } |
| 324 | memset(cap_devices, 0, cap_nr_devs * sizeof(struct cap_dev)); |
| 325 | |
| 326 | /* Initialize each device. */ |
| 327 | for (i = 0; i < cap_nr_devs; i++) { |
| 328 | cap_devices[i].node_size = cap_node_size; |
| 329 | init_MUTEX(&cap_devices[i].sem); |
| 330 | cap_setup_cdev(&cap_devices[i], i); |
| 331 | } |
| 332 | |
| 333 | return 0; |
| 334 | |
| 335 | fail: |
| 336 | cap_cleanup_module(); |
| 337 | return result; |
| 338 | } |
| 339 | |
| 340 | module_init(cap_init_module); |
| 341 | module_exit(cap_cleanup_module); |
| 342 | |
| 343 | char *cap_hash(char *plain_text, unsigned int plain_text_size, |
| 344 | char *key, unsigned int key_size) |
| 345 | { |
| 346 | struct scatterlist sg; |
| 347 | char *result = (char *) kmalloc(MAX_DIGEST_SIZE, GFP_KERNEL); |
| 348 | struct crypto_hash *tfm; |
| 349 | struct hash_desc desc; |
| 350 | int ret; |
| 351 | |
| 352 | tfm = crypto_alloc_hash("hmac(sha1)", 0, CRYPTO_ALG_ASYNC); |
| 353 | if (IS_ERR(tfm)) { |
| 354 | printk("failed to load transform for hmac(sha1): %ld\n", |
| 355 | PTR_ERR(tfm)); |
| 356 | kfree(result); |
| 357 | return NULL; |
| 358 | } |
| 359 | |
| 360 | desc.tfm = tfm; |
| 361 | desc.flags = 0; |
| 362 | |
| 363 | memset(result, 0, MAX_DIGEST_SIZE); |
| 364 | sg_set_buf(&sg, plain_text, plain_text_size); |
| 365 | |
| 366 | ret = crypto_hash_setkey(tfm, key, key_size); |
| 367 | if (ret) { |
| 368 | printk("setkey() failed ret=%d\n", ret); |
| 369 | kfree(result); |
| 370 | result = NULL; |
| 371 | goto out; |
| 372 | } |
| 373 | |
| 374 | ret = crypto_hash_digest(&desc, &sg, plain_text_size, result); |
| 375 | if (ret) { |
| 376 | printk("digest () failed ret=%d\n", ret); |
| 377 | kfree(result); |
| 378 | result = NULL; |
| 379 | goto out; |
| 380 | } |
| 381 | |
| 382 | printk("crypto hash digest size %d\n", |
| 383 | crypto_hash_digestsize(tfm)); |
| 384 | hexdump(result, MAX_DIGEST_SIZE); |
| 385 | |
| 386 | out: |
| 387 | crypto_free_hash(tfm); |
| 388 | return result; |
| 389 | } |