[PATCH] selinuxfs cleanups: sel_fill_super exit path
[linux-3.10.git] / security / seclvl.c
1 /**
2  * BSD Secure Levels LSM
3  *
4  * Maintainers:
5  *      Michael A. Halcrow <mike@halcrow.us>
6  *      Serge Hallyn <hallyn@cs.wm.edu>
7  *
8  * Copyright (c) 2001 WireX Communications, Inc <chris@wirex.com>
9  * Copyright (c) 2001 Greg Kroah-Hartman <greg@kroah.com>
10  * Copyright (c) 2002 International Business Machines <robb@austin.ibm.com>
11  *
12  *      This program is free software; you can redistribute it and/or modify
13  *      it under the terms of the GNU General Public License as published by
14  *      the Free Software Foundation; either version 2 of the License, or
15  *      (at your option) any later version.
16  */
17
18 #include <linux/config.h>
19 #include <linux/module.h>
20 #include <linux/moduleparam.h>
21 #include <linux/kernel.h>
22 #include <linux/init.h>
23 #include <linux/security.h>
24 #include <linux/netlink.h>
25 #include <linux/fs.h>
26 #include <linux/namei.h>
27 #include <linux/mount.h>
28 #include <linux/capability.h>
29 #include <linux/time.h>
30 #include <linux/proc_fs.h>
31 #include <linux/kobject.h>
32 #include <linux/crypto.h>
33 #include <asm/scatterlist.h>
34 #include <linux/gfp.h>
35 #include <linux/sysfs.h>
36
37 #define SHA1_DIGEST_SIZE 20
38
39 /**
40  * Module parameter that defines the initial secure level.
41  *
42  * When built as a module, it defaults to seclvl 1, which is the
43  * behavior of BSD secure levels.  Note that this default behavior
44  * wrecks havoc on a machine when the seclvl module is compiled into
45  * the kernel.  In that case, we default to seclvl 0.
46  */
47 #ifdef CONFIG_SECURITY_SECLVL_MODULE
48 static int initlvl = 1;
49 #else
50 static int initlvl;
51 #endif
52 module_param(initlvl, int, 0);
53 MODULE_PARM_DESC(initlvl, "Initial secure level (defaults to 1)");
54
55 /* Module parameter that defines the verbosity level */
56 static int verbosity;
57 module_param(verbosity, int, 0);
58 MODULE_PARM_DESC(verbosity, "Initial verbosity level (0 or 1; defaults to "
59                  "0, which is Quiet)");
60
61 /**
62  * Optional password which can be passed in to bring seclvl to 0
63  * (i.e., for halt/reboot).  Defaults to NULL (the passwd attribute
64  * file will not be registered in sysfs).
65  *
66  * This gets converted to its SHA1 hash when stored.  It's probably
67  * not a good idea to use this parameter when loading seclvl from a
68  * script; use sha1_passwd instead.
69  */
70
71 #define MAX_PASSWD_SIZE 32
72 static char passwd[MAX_PASSWD_SIZE];
73 module_param_string(passwd, passwd, sizeof(passwd), 0);
74 MODULE_PARM_DESC(passwd,
75                  "Plaintext of password that sets seclvl=0 when written to "
76                  "(sysfs mount point)/seclvl/passwd\n");
77
78 /**
79  * SHA1 hashed version of the optional password which can be passed in
80  * to bring seclvl to 0 (i.e., for halt/reboot).  Must be in
81  * hexadecimal format (40 characters).  Defaults to NULL (the passwd
82  * attribute file will not be registered in sysfs).
83  *
84  * Use the sha1sum utility to generate the SHA1 hash of a password:
85  *
86  * echo -n "secret" | sha1sum
87  */
88 #define MAX_SHA1_PASSWD 41
89 static char sha1_passwd[MAX_SHA1_PASSWD];
90 module_param_string(sha1_passwd, sha1_passwd, sizeof(sha1_passwd), 0);
91 MODULE_PARM_DESC(sha1_passwd,
92                  "SHA1 hash (40 hexadecimal characters) of password that "
93                  "sets seclvl=0 when plaintext password is written to "
94                  "(sysfs mount point)/seclvl/passwd\n");
95
96 static int hideHash = 1;
97 module_param(hideHash, int, 0);
98 MODULE_PARM_DESC(hideHash, "When set to 0, reading seclvl/passwd from sysfs "
99                  "will return the SHA1-hashed value of the password that "
100                  "lowers the secure level to 0.\n");
101
102 #define MY_NAME "seclvl"
103
104 /**
105  * This time-limits log writes to one per second.
106  */
107 #define seclvl_printk(verb, type, fmt, arg...)                  \
108         do {                                                    \
109                 if (verbosity >= verb) {                        \
110                         static unsigned long _prior;            \
111                         unsigned long _now = jiffies;           \
112                         if ((_now - _prior) > HZ) {             \
113                                 printk(type "%s: %s: " fmt,     \
114                                         MY_NAME, __FUNCTION__ , \
115                                         ## arg);                \
116                                 _prior = _now;                  \
117                         }                                       \
118                 }                                               \
119         } while (0)
120
121 /**
122  * The actual security level.  Ranges between -1 and 2 inclusive.
123  */
124 static int seclvl;
125
126 /**
127  * flag to keep track of how we were registered
128  */
129 static int secondary;
130
131 /**
132  * Verifies that the requested secure level is valid, given the current
133  * secure level.
134  */
135 static int seclvl_sanity(int reqlvl)
136 {
137         if ((reqlvl < -1) || (reqlvl > 2)) {
138                 seclvl_printk(1, KERN_WARNING, "Attempt to set seclvl out of "
139                               "range: [%d]\n", reqlvl);
140                 return -EINVAL;
141         }
142         if ((seclvl == 0) && (reqlvl == -1))
143                 return 0;
144         if (reqlvl < seclvl) {
145                 seclvl_printk(1, KERN_WARNING, "Attempt to lower seclvl to "
146                               "[%d]\n", reqlvl);
147                 return -EPERM;
148         }
149         return 0;
150 }
151
152 /**
153  * security level advancement rules:
154  *   Valid levels are -1 through 2, inclusive.
155  *   From -1, stuck.  [ in case compiled into kernel ]
156  *   From 0 or above, can only increment.
157  */
158 static void do_seclvl_advance(void *data, u64 val)
159 {
160         int ret;
161         int newlvl = (int)val;
162
163         ret = seclvl_sanity(newlvl);
164         if (ret)
165                 return;
166
167         if (newlvl > 2) {
168                 seclvl_printk(1, KERN_WARNING, "Cannot advance to seclvl "
169                               "[%d]\n", newlvl);
170                 return;
171         }
172         if (seclvl == -1) {
173                 seclvl_printk(1, KERN_WARNING, "Not allowed to advance to "
174                               "seclvl [%d]\n", seclvl);
175                 return;
176         }
177         seclvl = newlvl;  /* would it be more "correct" to set *data? */
178         return;
179 }
180
181 static u64 seclvl_int_get(void *data)
182 {
183         return *(int *)data;
184 }
185
186 DEFINE_SIMPLE_ATTRIBUTE(seclvl_file_ops, seclvl_int_get, do_seclvl_advance, "%lld\n");
187
188 static unsigned char hashedPassword[SHA1_DIGEST_SIZE];
189
190 /**
191  * Converts a block of plaintext of into its SHA1 hashed value.
192  *
193  * It would be nice if crypto had a wrapper to do this for us linear
194  * people...
195  */
196 static int
197 plaintext_to_sha1(unsigned char *hash, const char *plaintext, int len)
198 {
199         char *pgVirtAddr;
200         struct crypto_tfm *tfm;
201         struct scatterlist sg[1];
202         if (len > PAGE_SIZE) {
203                 seclvl_printk(0, KERN_ERR, "Plaintext password too large (%d "
204                               "characters).  Largest possible is %lu "
205                               "bytes.\n", len, PAGE_SIZE);
206                 return -ENOMEM;
207         }
208         tfm = crypto_alloc_tfm("sha1", CRYPTO_TFM_REQ_MAY_SLEEP);
209         if (tfm == NULL) {
210                 seclvl_printk(0, KERN_ERR,
211                               "Failed to load transform for SHA1\n");
212                 return -ENOSYS;
213         }
214         // Just get a new page; don't play around with page boundaries
215         // and scatterlists.
216         pgVirtAddr = (char *)__get_free_page(GFP_KERNEL);
217         sg[0].page = virt_to_page(pgVirtAddr);
218         sg[0].offset = 0;
219         sg[0].length = len;
220         strncpy(pgVirtAddr, plaintext, len);
221         crypto_digest_init(tfm);
222         crypto_digest_update(tfm, sg, 1);
223         crypto_digest_final(tfm, hash);
224         crypto_free_tfm(tfm);
225         free_page((unsigned long)pgVirtAddr);
226         return 0;
227 }
228
229 /**
230  * Called whenever the user writes to the sysfs passwd handle to this kernel
231  * object.  It hashes the password and compares the hashed results.
232  */
233 static ssize_t
234 passwd_write_file(struct file * file, const char __user * buf,
235                                 size_t count, loff_t *ppos)
236 {
237         int i;
238         unsigned char tmp[SHA1_DIGEST_SIZE];
239         char *page;
240         int rc;
241         int len;
242
243         if (!*passwd && !*sha1_passwd) {
244                 seclvl_printk(0, KERN_ERR, "Attempt to password-unlock the "
245                               "seclvl module, but neither a plain text "
246                               "password nor a SHA1 hashed password was "
247                               "passed in as a module parameter!  This is a "
248                               "bug, since it should not be possible to be in "
249                               "this part of the module; please tell a "
250                               "maintainer about this event.\n");
251                 return -EINVAL;
252         }
253
254         if (count < 0 || count >= PAGE_SIZE)
255                 return -EINVAL;
256         if (*ppos != 0)
257                 return -EINVAL;
258         page = (char *)get_zeroed_page(GFP_KERNEL);
259         if (!page)
260                 return -ENOMEM;
261         len = -EFAULT;
262         if (copy_from_user(page, buf, count))
263                 goto out;
264         
265         len = strlen(page);
266         /* ``echo "secret" > seclvl/passwd'' includes a newline */
267         if (page[len - 1] == '\n')
268                 len--;
269         /* Hash the password, then compare the hashed values */
270         if ((rc = plaintext_to_sha1(tmp, page, len))) {
271                 seclvl_printk(0, KERN_ERR, "Error hashing password: rc = "
272                               "[%d]\n", rc);
273                 return rc;
274         }
275         for (i = 0; i < SHA1_DIGEST_SIZE; i++) {
276                 if (hashedPassword[i] != tmp[i])
277                         return -EPERM;
278         }
279         seclvl_printk(0, KERN_INFO,
280                       "Password accepted; seclvl reduced to 0.\n");
281         seclvl = 0;
282         len = count;
283
284 out:
285         free_page((unsigned long)page);
286         return len;
287 }
288
289 static struct file_operations passwd_file_ops = {
290         .write = passwd_write_file,
291 };
292
293 /**
294  * Explicitely disallow ptrace'ing the init process.
295  */
296 static int seclvl_ptrace(struct task_struct *parent, struct task_struct *child)
297 {
298         if (seclvl >= 0) {
299                 if (child->pid == 1) {
300                         seclvl_printk(1, KERN_WARNING, "Attempt to ptrace "
301                                       "the init process dissallowed in "
302                                       "secure level %d\n", seclvl);
303                         return -EPERM;
304                 }
305         }
306         return 0;
307 }
308
309 /**
310  * Capability checks for seclvl.  The majority of the policy
311  * enforcement for seclvl takes place here.
312  */
313 static int seclvl_capable(struct task_struct *tsk, int cap)
314 {
315         /* init can do anything it wants */
316         if (tsk->pid == 1)
317                 return 0;
318
319         switch (seclvl) {
320         case 2:
321                 /* fall through */
322         case 1:
323                 if (cap == CAP_LINUX_IMMUTABLE) {
324                         seclvl_printk(1, KERN_WARNING, "Attempt to modify "
325                                       "the IMMUTABLE and/or APPEND extended "
326                                       "attribute on a file with the IMMUTABLE "
327                                       "and/or APPEND extended attribute set "
328                                       "denied in seclvl [%d]\n", seclvl);
329                         return -EPERM;
330                 } else if (cap == CAP_SYS_RAWIO) {      // Somewhat broad...
331                         seclvl_printk(1, KERN_WARNING, "Attempt to perform "
332                                       "raw I/O while in secure level [%d] "
333                                       "denied\n", seclvl);
334                         return -EPERM;
335                 } else if (cap == CAP_NET_ADMIN) {
336                         seclvl_printk(1, KERN_WARNING, "Attempt to perform "
337                                       "network administrative task while "
338                                       "in secure level [%d] denied\n", seclvl);
339                         return -EPERM;
340                 } else if (cap == CAP_SETUID) {
341                         seclvl_printk(1, KERN_WARNING, "Attempt to setuid "
342                                       "while in secure level [%d] denied\n",
343                                       seclvl);
344                         return -EPERM;
345                 } else if (cap == CAP_SETGID) {
346                         seclvl_printk(1, KERN_WARNING, "Attempt to setgid "
347                                       "while in secure level [%d] denied\n",
348                                       seclvl);
349                 } else if (cap == CAP_SYS_MODULE) {
350                         seclvl_printk(1, KERN_WARNING, "Attempt to perform "
351                                       "a module operation while in secure "
352                                       "level [%d] denied\n", seclvl);
353                         return -EPERM;
354                 }
355                 break;
356         default:
357                 break;
358         }
359         /* from dummy.c */
360         if (cap_is_fs_cap(cap) ? tsk->fsuid == 0 : tsk->euid == 0)
361                 return 0;       /* capability granted */
362         seclvl_printk(1, KERN_WARNING, "Capability denied\n");
363         return -EPERM;          /* capability denied */
364 }
365
366 /**
367  * Disallow reversing the clock in seclvl > 1
368  */
369 static int seclvl_settime(struct timespec *tv, struct timezone *tz)
370 {
371         if (tv && seclvl > 1) {
372                 struct timespec now;
373                 now = current_kernel_time();
374                 if (tv->tv_sec < now.tv_sec ||
375                     (tv->tv_sec == now.tv_sec && tv->tv_nsec < now.tv_nsec)) {
376                         seclvl_printk(1, KERN_WARNING, "Attempt to decrement "
377                                       "time in secure level %d denied: "
378                                       "current->pid = [%d], "
379                                       "current->group_leader->pid = [%d]\n",
380                                       seclvl, current->pid,
381                                       current->group_leader->pid);
382                         return -EPERM;
383                 }               /* if attempt to decrement time */
384         }                       /* if seclvl > 1 */
385         return 0;
386 }
387
388 /* claim the blockdev to exclude mounters, release on file close */
389 static int seclvl_bd_claim(struct inode *inode)
390 {
391         int holder;
392         struct block_device *bdev = NULL;
393         dev_t dev = inode->i_rdev;
394         bdev = open_by_devnum(dev, FMODE_WRITE);
395         if (bdev) {
396                 if (bd_claim(bdev, &holder)) {
397                         blkdev_put(bdev);
398                         return -EPERM;
399                 }
400                 /* claimed, mark it to release on close */
401                 inode->i_security = current;
402         }
403         return 0;
404 }
405
406 /* release the blockdev if you claimed it */
407 static void seclvl_bd_release(struct inode *inode)
408 {
409         if (inode && S_ISBLK(inode->i_mode) && inode->i_security == current) {
410                 struct block_device *bdev = inode->i_bdev;
411                 if (bdev) {
412                         bd_release(bdev);
413                         blkdev_put(bdev);
414                         inode->i_security = NULL;
415                 }
416         }
417 }
418
419 /**
420  * Security for writes to block devices is regulated by this seclvl
421  * function.  Deny all writes to block devices in seclvl 2.  In
422  * seclvl 1, we only deny writes to *mounted* block devices.
423  */
424 static int
425 seclvl_inode_permission(struct inode *inode, int mask, struct nameidata *nd)
426 {
427         if (current->pid != 1 && S_ISBLK(inode->i_mode) && (mask & MAY_WRITE)) {
428                 switch (seclvl) {
429                 case 2:
430                         seclvl_printk(1, KERN_WARNING, "Write to block device "
431                                       "denied in secure level [%d]\n", seclvl);
432                         return -EPERM;
433                 case 1:
434                         if (seclvl_bd_claim(inode)) {
435                                 seclvl_printk(1, KERN_WARNING,
436                                               "Write to mounted block device "
437                                               "denied in secure level [%d]\n",
438                                               seclvl);
439                                 return -EPERM;
440                         }
441                 }
442         }
443         return 0;
444 }
445
446 /**
447  * The SUID and SGID bits cannot be set in seclvl >= 1
448  */
449 static int seclvl_inode_setattr(struct dentry *dentry, struct iattr *iattr)
450 {
451         if (seclvl > 0) {
452                 if (iattr->ia_valid & ATTR_MODE)
453                         if (iattr->ia_mode & S_ISUID ||
454                             iattr->ia_mode & S_ISGID) {
455                                 seclvl_printk(1, KERN_WARNING, "Attempt to "
456                                               "modify SUID or SGID bit "
457                                               "denied in seclvl [%d]\n",
458                                               seclvl);
459                                 return -EPERM;
460                         }
461         }
462         return 0;
463 }
464
465 /* release busied block devices */
466 static void seclvl_file_free_security(struct file *filp)
467 {
468         struct dentry *dentry = filp->f_dentry;
469         struct inode *inode = NULL;
470
471         if (dentry) {
472                 inode = dentry->d_inode;
473                 seclvl_bd_release(inode);
474         }
475 }
476
477 /**
478  * Cannot unmount in secure level 2
479  */
480 static int seclvl_umount(struct vfsmount *mnt, int flags)
481 {
482         if (current->pid == 1)
483                 return 0;
484         if (seclvl == 2) {
485                 seclvl_printk(1, KERN_WARNING, "Attempt to unmount in secure "
486                               "level %d\n", seclvl);
487                 return -EPERM;
488         }
489         return 0;
490 }
491
492 static struct security_operations seclvl_ops = {
493         .ptrace = seclvl_ptrace,
494         .capable = seclvl_capable,
495         .inode_permission = seclvl_inode_permission,
496         .inode_setattr = seclvl_inode_setattr,
497         .file_free_security = seclvl_file_free_security,
498         .settime = seclvl_settime,
499         .sb_umount = seclvl_umount,
500 };
501
502 /**
503  * Process the password-related module parameters
504  */
505 static int processPassword(void)
506 {
507         int rc = 0;
508         hashedPassword[0] = '\0';
509         if (*passwd) {
510                 if (*sha1_passwd) {
511                         seclvl_printk(0, KERN_ERR, "Error: Both "
512                                       "passwd and sha1_passwd "
513                                       "were set, but they are mutually "
514                                       "exclusive.\n");
515                         return -EINVAL;
516                 }
517                 if ((rc = plaintext_to_sha1(hashedPassword, passwd,
518                                             strlen(passwd)))) {
519                         seclvl_printk(0, KERN_ERR, "Error: SHA1 support not "
520                                       "in kernel\n");
521                         return rc;
522                 }
523                 /* All static data goes to the BSS, which zero's the
524                  * plaintext password out for us. */
525         } else if (*sha1_passwd) {      // Base 16
526                 int i;
527                 i = strlen(sha1_passwd);
528                 if (i != (SHA1_DIGEST_SIZE * 2)) {
529                         seclvl_printk(0, KERN_ERR, "Received [%d] bytes; "
530                                       "expected [%d] for the hexadecimal "
531                                       "representation of the SHA1 hash of "
532                                       "the password.\n",
533                                       i, (SHA1_DIGEST_SIZE * 2));
534                         return -EINVAL;
535                 }
536                 while ((i -= 2) + 2) {
537                         unsigned char tmp;
538                         tmp = sha1_passwd[i + 2];
539                         sha1_passwd[i + 2] = '\0';
540                         hashedPassword[i / 2] = (unsigned char)
541                             simple_strtol(&sha1_passwd[i], NULL, 16);
542                         sha1_passwd[i + 2] = tmp;
543                 }
544         }
545         return 0;
546 }
547
548 /**
549  * securityfs registrations
550  */
551 struct dentry *dir_ino, *seclvl_ino, *passwd_ino;
552
553 static int seclvlfs_register(void)
554 {
555         dir_ino = securityfs_create_dir("seclvl", NULL);
556         if (!dir_ino)
557                 return -EFAULT;
558
559         seclvl_ino = securityfs_create_file("seclvl", S_IRUGO | S_IWUSR,
560                                 dir_ino, &seclvl, &seclvl_file_ops);
561         if (!seclvl_ino)
562                 goto out_deldir;
563         if (*passwd || *sha1_passwd) {
564                 passwd_ino = securityfs_create_file("passwd", S_IRUGO | S_IWUSR,
565                                 dir_ino, NULL, &passwd_file_ops);
566                 if (!passwd_ino)
567                         goto out_delf;
568         }
569         return 0;
570
571 out_deldir:
572         securityfs_remove(dir_ino);
573 out_delf:
574         securityfs_remove(seclvl_ino);
575
576         return -EFAULT;
577 }
578
579 /**
580  * Initialize the seclvl module.
581  */
582 static int __init seclvl_init(void)
583 {
584         int rc = 0;
585         if (verbosity < 0 || verbosity > 1) {
586                 printk(KERN_ERR "Error: bad verbosity [%d]; only 0 or 1 "
587                        "are valid values\n", verbosity);
588                 rc = -EINVAL;
589                 goto exit;
590         }
591         if (initlvl < -1 || initlvl > 2) {
592                 seclvl_printk(0, KERN_ERR, "Error: bad initial securelevel "
593                               "[%d].\n", initlvl);
594                 rc = -EINVAL;
595                 goto exit;
596         }
597         seclvl = initlvl;
598         if ((rc = processPassword())) {
599                 seclvl_printk(0, KERN_ERR, "Error processing the password "
600                               "module parameter(s): rc = [%d]\n", rc);
601                 goto exit;
602         }
603         /* register ourselves with the security framework */
604         if (register_security(&seclvl_ops)) {
605                 seclvl_printk(0, KERN_ERR,
606                               "seclvl: Failure registering with the "
607                               "kernel.\n");
608                 /* try registering with primary module */
609                 rc = mod_reg_security(MY_NAME, &seclvl_ops);
610                 if (rc) {
611                         seclvl_printk(0, KERN_ERR, "seclvl: Failure "
612                                       "registering with primary security "
613                                       "module.\n");
614                         goto exit;
615                 }               /* if primary module registered */
616                 secondary = 1;
617         }                       /* if we registered ourselves with the security framework */
618         if ((rc = seclvlfs_register())) {
619                 seclvl_printk(0, KERN_ERR, "Error registering with sysfs\n");
620                 goto exit;
621         }
622         seclvl_printk(0, KERN_INFO, "seclvl: Successfully initialized.\n");
623  exit:
624         if (rc) {
625                 printk(KERN_ERR "seclvl: Error during initialization: rc = "
626                        "[%d]\n", rc);
627         }
628         return rc;
629 }
630
631 /**
632  * Remove the seclvl module.
633  */
634 static void __exit seclvl_exit(void)
635 {
636         securityfs_remove(seclvl_ino);
637         if (*passwd || *sha1_passwd)
638                 securityfs_remove(passwd_ino);
639         securityfs_remove(dir_ino);
640         if (secondary == 1) {
641                 mod_unreg_security(MY_NAME, &seclvl_ops);
642         } else if (unregister_security(&seclvl_ops)) {
643                 seclvl_printk(0, KERN_INFO,
644                               "seclvl: Failure unregistering with the "
645                               "kernel\n");
646         }
647 }
648
649 module_init(seclvl_init);
650 module_exit(seclvl_exit);
651
652 MODULE_AUTHOR("Michael A. Halcrow <mike@halcrow.us>");
653 MODULE_DESCRIPTION("LSM implementation of the BSD Secure Levels");
654 MODULE_LICENSE("GPL");