summaryrefslogtreecommitdiffstats
path: root/kernel/cred.c
blob: f3ca1066061715bd5c2e9f0dd93c8576fa9617d0 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
/* Task credentials management - see Documentation/credentials.txt
 *
 * Copyright (C) 2008 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public Licence
 * as published by the Free Software Foundation; either version
 * 2 of the Licence, or (at your option) any later version.
 */
#include <linux/module.h>
#include <linux/cred.h>
#include <linux/sched.h>
#include <linux/key.h>
#include <linux/keyctl.h>
#include <linux/init_task.h>
#include <linux/security.h>
#include <linux/cn_proc.h>
#include "cred-internals.h"

static struct kmem_cache *cred_jar;

/*
 * The common credentials for the initial task's thread group
 */
#ifdef CONFIG_KEYS
static struct thread_group_cred init_tgcred = {
	.usage	= ATOMIC_INIT(2),
	.tgid	= 0,
	.lock	= SPIN_LOCK_UNLOCKED,
};
#endif

/*
 * The initial credentials for the initial task
 */
struct cred init_cred = {
	.usage			= ATOMIC_INIT(4),
	.securebits		= SECUREBITS_DEFAULT,
	.cap_inheritable	= CAP_INIT_INH_SET,
	.cap_permitted		= CAP_FULL_SET,
	.cap_effective		= CAP_INIT_EFF_SET,
	.cap_bset		= CAP_INIT_BSET,
	.user			= INIT_USER,
	.group_info		= &init_groups,
#ifdef CONFIG_KEYS
	.tgcred			= &init_tgcred,
#endif
};

/*
 * Dispose of the shared task group credentials
 */
#ifdef CONFIG_KEYS
static void release_tgcred_rcu(struct rcu_head *rcu)
{
	struct thread_group_cred *tgcred =
		container_of(rcu, struct thread_group_cred, rcu);

	BUG_ON(atomic_read(&tgcred->usage) != 0);

	key_put(tgcred->session_keyring);
	key_put(tgcred->process_keyring);
	kfree(tgcred);
}
#endif

/*
 * Release a set of thread group credentials.
 */
static void release_tgcred(struct cred *cred)
{
#ifdef CONFIG_KEYS
	struct thread_group_cred *tgcred = cred->tgcred;

	if (atomic_dec_and_test(&tgcred->usage))
		call_rcu(&tgcred->rcu, release_tgcred_rcu);
#endif
}

/*
 * The RCU callback to actually dispose of a set of credentials
 */
static void put_cred_rcu(struct rcu_head *rcu)
{
	struct cred *cred = container_of(rcu, struct cred, rcu);

	if (atomic_read(&cred->usage) != 0)
		panic("CRED: put_cred_rcu() sees %p with usage %d\n",
		      cred, atomic_read(&cred->usage));

	security_cred_free(cred);
	key_put(cred->thread_keyring);
	key_put(cred->request_key_auth);
	release_tgcred(cred);
	put_group_info(cred->group_info);
	free_uid(cred->user);
	kmem_cache_free(cred_jar, cred);
}

/**
 * __put_cred - Destroy a set of credentials
 * @cred: The record to release
 *
 * Destroy a set of credentials on which no references remain.
 */
void __put_cred(struct cred *cred)
{
	BUG_ON(atomic_read(&cred->usage) != 0);

	call_rcu(&cred->rcu, put_cred_rcu);
}
EXPORT_SYMBOL(__put_cred);

/**
 * prepare_creds - Prepare a new set of credentials for modification
 *
 * Prepare a new set of task credentials for modification.  A task's creds
 * shouldn't generally be modified directly, therefore this function is used to
 * prepare a new copy, which the caller then modifies and then commits by
 * calling commit_creds().
 *
 * Preparation involves making a copy of the objective creds for modification.
 *
 * Returns a pointer to the new creds-to-be if successful, NULL otherwise.
 *
 * Call commit_creds() or abort_creds() to clean up.
 */
struct cred *prepare_creds(void)
{
	struct task_struct *task = current;
	const struct cred *old;
	struct cred *new;

	BUG_ON(atomic_read(&task->real_cred->usage) < 1);

	new = kmem_cache_alloc(cred_jar, GFP_KERNEL);
	if (!new)
		return NULL;

	old = task->cred;
	memcpy(new, old, sizeof(struct cred));

	atomic_set(&new->usage, 1);
	get_group_info(new->group_info);
	get_uid(new->user);

#ifdef CONFIG_KEYS
	key_get(new->thread_keyring);
	key_get(new->request_key_auth);
	atomic_inc(&new->tgcred->usage);
#endif

#ifdef CONFIG_SECURITY
	new->security = NULL;
#endif

	if (security_prepare_creds(new, old, GFP_KERNEL) < 0)
		goto error;
	return new;

error:
	abort_creds(new);
	return NULL;
}
EXPORT_SYMBOL(prepare_creds);

/*
 * Prepare credentials for current to perform an execve()
 * - The caller must hold current->cred_exec_mutex
 */
struct cred *prepare_exec_creds(void)
{
	struct thread_group_cred *tgcred = NULL;
	struct cred *new;

#ifdef CONFIG_KEYS
	tgcred = kmalloc(sizeof(*tgcred), GFP_KERNEL);
	if (!tgcred)
		return NULL;
#endif

	new = prepare_creds();
	if (!new) {
		kfree(tgcred);
		return new;
	}

#ifdef CONFIG_KEYS
	/* newly exec'd tasks don't get a thread keyring */
	key_put(new->thread_keyring);
	new->thread_keyring = NULL;

	/* create a new per-thread-group creds for all this set of threads to
	 * share */
	memcpy(tgcred, new->tgcred, sizeof(struct thread_group_cred));

	atomic_set(&tgcred->usage, 1);
	spin_lock_init(&tgcred->lock);

	/* inherit the session keyring; new process keyring */
	key_get(tgcred->session_keyring);
	tgcred->process_keyring = NULL;

	release_tgcred(new);
	new->tgcred = tgcred;
#endif

	return new;
}

/*
 * prepare new credentials for the usermode helper dispatcher
 */
struct cred *prepare_usermodehelper_creds(void)
{
#ifdef CONFIG_KEYS
	struct thread_group_cred *tgcred = NULL;
#endif
	struct cred *new;

#ifdef CONFIG_KEYS
	tgcred = kzalloc(sizeof(*new->tgcred), GFP_ATOMIC);
	if (!tgcred)
		return NULL;
#endif

	new = kmem_cache_alloc(cred_jar, GFP_ATOMIC);
	if (!new)
		return NULL;

	memcpy(new, &init_cred, sizeof(struct cred));

	atomic_set(&new->usage, 1);
	get_group_info(new->group_info);
	get_uid(new->user);

#ifdef CONFIG_KEYS
	new->thread_keyring = NULL;
	new->request_key_auth = NULL;
	new->jit_keyring = KEY_REQKEY_DEFL_DEFAULT;

	atomic_set(&tgcred->usage, 1);
	spin_lock_init(&tgcred->lock);
	new->tgcred = tgcred;
#endif

#ifdef CONFIG_SECURITY
	new->security = NULL;
#endif
	if (security_prepare_creds(new, &init_cred, GFP_ATOMIC) < 0)
		goto error;

	BUG_ON(atomic_read(&new->usage) != 1);
	return new;

error:
	put_cred(new);
	return NULL;
}

/*
 * Copy credentials for the new process created by fork()
 *
 * We share if we can, but under some circumstances we have to generate a new
 * set.
 *
 * The new process gets the current process's subjective credentials as its
 * objective and subjective credentials
 */
int copy_creds(struct task_struct *p, unsigned long clone_flags)
{
#ifdef CONFIG_KEYS
	struct thread_group_cred *tgcred;
#endif
	struct cred *new;

	mutex_init(&p->cred_exec_mutex);

	if (
#ifdef CONFIG_KEYS
		!p->cred->thread_keyring &&
#endif
		clone_flags & CLONE_THREAD
	    ) {
		p->real_cred = get_cred(p->cred);
		get_cred(p->cred);
		atomic_inc(&p->cred->user->processes);
		return 0;
	}

	new = prepare_creds();
	if (!new)
		return -ENOMEM;

#ifdef CONFIG_KEYS
	/* new threads get their own thread keyrings if their parent already
	 * had one */
	if (new->thread_keyring) {
		key_put(new->thread_keyring);
		new->thread_keyring = NULL;
		if (clone_flags & CLONE_THREAD)
			install_thread_keyring_to_cred(new);
	}

	/* we share the process and session keyrings between all the threads in
	 * a process - this is slightly icky as we violate COW credentials a
	 * bit */
	if (!(clone_flags & CLONE_THREAD)) {
		tgcred = kmalloc(sizeof(*tgcred), GFP_KERNEL);
		if (!tgcred) {
			put_cred(new);
			return -ENOMEM;
		}
		atomic_set(&tgcred->usage, 1);
		spin_lock_init(&tgcred->lock);
		tgcred->process_keyring = NULL;
		tgcred->session_keyring = key_get(new->tgcred->session_keyring);

		release_tgcred(new);
		new->tgcred = tgcred;
	}
#endif

	atomic_inc(&new->user->processes);
	p->cred = p->real_cred = get_cred(new);
	return 0;
}

/**
 * commit_creds - Install new credentials upon the current task
 * @new: The credentials to be assigned
 *
 * Install a new set of credentials to the current task, using RCU to replace
 * the old set.  Both the objective and the subjective credentials pointers are
 * updated.  This function may not be called if the subjective credentials are
 * in an overridden state.
 *
 * This function eats the caller's reference to the new credentials.
 *
 * Always returns 0 thus allowing this function to be tail-called at the end
 * of, say, sys_setgid().
 */
int commit_creds(struct cred *new)
{
	struct task_struct *task = current;
	const struct cred *old;

	BUG_ON(task->cred != task->real_cred);
	BUG_ON(atomic_read(&task->real_cred->usage) < 2);
	BUG_ON(atomic_read(&new->usage) < 1);

	old = task->real_cred;
	security_commit_creds(new, old);

	get_cred(new); /* we will require a ref for the subj creds too */

	/* dumpability changes */
	if (old->euid != new->euid ||
	    old->egid != new->egid ||
	    old->fsuid != new->fsuid ||
	    old->fsgid != new->fsgid ||
	    !cap_issubset(new->cap_permitted, old->cap_permitted)) {
		set_dumpable(task->mm, suid_dumpable);
		task->pdeath_signal = 0;
		smp_wmb();
	}

	/* alter the thread keyring */
	if (new->fsuid != old->fsuid)
		key_fsuid_changed(task);
	if (new->fsgid != old->fsgid)
		key_fsgid_changed(task);

	/* do it
	 * - What if a process setreuid()'s and this brings the
	 *   new uid over his NPROC rlimit?  We can check this now
	 *   cheaply with the new uid cache, so if it matters
	 *   we should be checking for it.  -DaveM
	 */
	if (new->user != old->user)
		atomic_inc(&new->user->processes);
	rcu_assign_pointer(task->real_cred, new);
	rcu_assign_pointer(task->cred, new);
	if (new->user != old->user)
		atomic_dec(&old->user->processes);

	sched_switch_user(task);

	/* send notifications */
	if (new->uid   != old->uid  ||
	    new->euid  != old->euid ||
	    new->suid  != old->suid ||
	    new->fsuid != old->fsuid)
		proc_id_connector(task, PROC_EVENT_UID);

	if (new->gid   != old->gid  ||
	    new->egid  != old->egid ||
	    new->sgid  != old->sgid ||
	    new->fsgid != old->fsgid)
		proc_id_connector(task, PROC_EVENT_GID);

	/* release the old obj and subj refs both */
	put_cred(old);
	put_cred(old);
	return 0;
}
EXPORT_SYMBOL(commit_creds);

/**
 * abort_creds - Discard a set of credentials and unlock the current task
 * @new: The credentials that were going to be applied
 *
 * Discard a set of credentials that were under construction and unlock the
 * current task.
 */
void abort_creds(struct cred *new)
{
	BUG_ON(atomic_read(&new->usage) < 1);
	put_cred(new);
}
EXPORT_SYMBOL(abort_creds);

/**
 * override_creds - Override the current process's subjective credentials
 * @new: The credentials to be assigned
 *
 * Install a set of temporary override subjective credentials on the current
 * process, returning the old set for later reversion.
 */
const struct cred *override_creds(const struct cred *new)
{
	const struct cred *old = current->cred;

	rcu_assign_pointer(current->cred, get_cred(new));
	return old;
}
EXPORT_SYMBOL(override_creds);

/**
 * revert_creds - Revert a temporary subjective credentials override
 * @old: The credentials to be restored
 *
 * Revert a temporary set of override subjective credentials to an old set,
 * discarding the override set.
 */
void revert_creds(const struct cred *old)
{
	const struct cred *override = current->cred;

	rcu_assign_pointer(current->cred, old);
	put_cred(override);
}
EXPORT_SYMBOL(revert_creds);

/*
 * initialise the credentials stuff
 */
void __init cred_init(void)
{
	/* allocate a slab in which we can store credentials */
	cred_jar = kmem_cache_create("cred_jar", sizeof(struct cred),
				     0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
}