aboutsummaryrefslogtreecommitdiff
path: root/security/commoncap.c
blob: 57673ee07ceb59b45a05167ab1766eb551ad4ac8 (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
/* Common capabilities, needed by capability.o and root_plug.o 
 *
 *	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/capability.h>
#include <linux/config.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/security.h>
#include <linux/file.h>
#include <linux/mm.h>
#include <linux/mman.h>
#include <linux/pagemap.h>
#include <linux/swap.h>
#include <linux/smp_lock.h>
#include <linux/skbuff.h>
#include <linux/netlink.h>
#include <linux/ptrace.h>
#include <linux/xattr.h>
#include <linux/hugetlb.h>

int cap_netlink_send(struct sock *sk, struct sk_buff *skb)
{
	NETLINK_CB(skb).eff_cap = current->cap_effective;
	return 0;
}

EXPORT_SYMBOL(cap_netlink_send);

int cap_netlink_recv(struct sk_buff *skb, int cap)
{
	if (!cap_raised(NETLINK_CB(skb).eff_cap, cap))
		return -EPERM;
	return 0;
}

EXPORT_SYMBOL(cap_netlink_recv);

int cap_capable (struct task_struct *tsk, int cap)
{
	/* Derived from include/linux/sched.h:capable. */
	if (cap_raised(tsk->cap_effective, cap))
		return 0;
	return -EPERM;
}

int cap_settime(struct timespec *ts, struct timezone *tz)
{
	if (!capable(CAP_SYS_TIME))
		return -EPERM;
	return 0;
}

int cap_ptrace (struct task_struct *parent, struct task_struct *child)
{
	/* Derived from arch/i386/kernel/ptrace.c:sys_ptrace. */
	if (!cap_issubset(child->cap_permitted, parent->cap_permitted) &&
	    !__capable(parent, CAP_SYS_PTRACE))
		return -EPERM;
	return 0;
}

int cap_capget (struct task_struct *target, kernel_cap_t *effective,
		kernel_cap_t *inheritable, kernel_cap_t *permitted)
{
	/* Derived from kernel/capability.c:sys_capget. */
	*effective = cap_t (target->cap_effective);
	*inheritable = cap_t (target->cap_inheritable);
	*permitted = cap_t (target->cap_permitted);
	return 0;
}

int cap_capset_check (struct task_struct *target, kernel_cap_t *effective,
		      kernel_cap_t *inheritable, kernel_cap_t *permitted)
{
	/* Derived from kernel/capability.c:sys_capset. */
	/* verify restrictions on target's new Inheritable set */
	if (!cap_issubset (*inheritable,
			   cap_combine (target->cap_inheritable,
					current->cap_permitted))) {
		return -EPERM;
	}

	/* verify restrictions on target's new Permitted set */
	if (!cap_issubset (*permitted,
			   cap_combine (target->cap_permitted,
					current->cap_permitted))) {
		return -EPERM;
	}

	/* verify the _new_Effective_ is a subset of the _new_Permitted_ */
	if (!cap_issubset (*effective, *permitted)) {
		return -EPERM;
	}

	return 0;
}

void cap_capset_set (struct task_struct *target, kernel_cap_t *effective,
		     kernel_cap_t *inheritable, kernel_cap_t *permitted)
{
	target->cap_effective = *effective;
	target->cap_inheritable = *inheritable;
	target->cap_permitted = *permitted;
}

int cap_bprm_set_security (struct linux_binprm *bprm)
{
	/* Copied from fs/exec.c:prepare_binprm. */

	/* We don't have VFS support for capabilities yet */
	cap_clear (bprm->cap_inheritable);
	cap_clear (bprm->cap_permitted);
	cap_clear (bprm->cap_effective);

	/*  To support inheritance of root-permissions and suid-root
	 *  executables under compatibility mode, we raise all three
	 *  capability sets for the file.
	 *
	 *  If only the real uid is 0, we only raise the inheritable
	 *  and permitted sets of the executable file.
	 */

	if (!issecure (SECURE_NOROOT)) {
		if (bprm->e_uid == 0 || current->uid == 0) {
			cap_set_full (bprm->cap_inheritable);
			cap_set_full (bprm->cap_permitted);
		}
		if (bprm->e_uid == 0)
			cap_set_full (bprm->cap_effective);
	}
	return 0;
}

void cap_bprm_apply_creds (struct linux_binprm *bprm, int unsafe)
{
	/* Derived from fs/exec.c:compute_creds. */
	kernel_cap_t new_permitted, working;

	new_permitted = cap_intersect (bprm->cap_permitted, cap_bset);
	working = cap_intersect (bprm->cap_inheritable,
				 current->cap_inheritable);
	new_permitted = cap_combine (new_permitted, working);

	if (bprm->e_uid != current->uid || bprm->e_gid != current->gid ||
	    !cap_issubset (new_permitted, current->cap_permitted)) {
		current->mm->dumpable = suid_dumpable;

		if (unsafe & ~LSM_UNSAFE_PTRACE_CAP) {
			if (!capable(CAP_SETUID)) {
				bprm->e_uid = current->uid;
				bprm->e_gid = current->gid;
			}
			if (!capable (CAP_SETPCAP)) {
				new_permitted = cap_intersect (new_permitted,
							current->cap_permitted);
			}
		}
	}

	current->suid = current->euid = current->fsuid = bprm->e_uid;
	current->sgid = current->egid = current->fsgid = bprm->e_gid;

	/* For init, we want to retain the capabilities set
	 * in the init_task struct. Thus we skip the usual
	 * capability rules */
	if (current->pid != 1) {
		current->cap_permitted = new_permitted;
		current->cap_effective =
		    cap_intersect (new_permitted, bprm->cap_effective);
	}

	/* AUD: Audit candidate if current->cap_effective is set */

	current->keep_capabilities = 0;
}

int cap_bprm_secureexec (struct linux_binprm *bprm)
{
	/* If/when this module is enhanced to incorporate capability
	   bits on files, the test below should be extended to also perform a 
	   test between the old and new capability sets.  For now,
	   it simply preserves the legacy decision algorithm used by
	   the old userland. */
	return (current->euid != current->uid ||
		current->egid != current->gid);
}

int cap_inode_setxattr(struct dentry *dentry, char *name, void *value,
		       size_t size, int flags)
{
	if (!strncmp(name, XATTR_SECURITY_PREFIX,
		     sizeof(XATTR_SECURITY_PREFIX) - 1)  &&
	    !capable(CAP_SYS_ADMIN))
		return -EPERM;
	return 0;
}

int cap_inode_removexattr(struct dentry *dentry, char *name)
{
	if (!strncmp(name, XATTR_SECURITY_PREFIX,
		     sizeof(XATTR_SECURITY_PREFIX) - 1)  &&
	    !capable(CAP_SYS_ADMIN))
		return -EPERM;
	return 0;
}

/* moved from kernel/sys.c. */
/* 
 * cap_emulate_setxuid() fixes the effective / permitted capabilities of
 * a process after a call to setuid, setreuid, or setresuid.
 *
 *  1) When set*uiding _from_ one of {r,e,s}uid == 0 _to_ all of
 *  {r,e,s}uid != 0, the permitted and effective capabilities are
 *  cleared.
 *
 *  2) When set*uiding _from_ euid == 0 _to_ euid != 0, the effective
 *  capabilities of the process are cleared.
 *
 *  3) When set*uiding _from_ euid != 0 _to_ euid == 0, the effective
 *  capabilities are set to the permitted capabilities.
 *
 *  fsuid is handled elsewhere. fsuid == 0 and {r,e,s}uid!= 0 should 
 *  never happen.
 *
 *  -astor 
 *
 * cevans - New behaviour, Oct '99
 * A process may, via prctl(), elect to keep its capabilities when it
 * calls setuid() and switches away from uid==0. Both permitted and
 * effective sets will be retained.
 * Without this change, it was impossible for a daemon to drop only some
 * of its privilege. The call to setuid(!=0) would drop all privileges!
 * Keeping uid 0 is not an option because uid 0 owns too many vital
 * files..
 * Thanks to Olaf Kirch and Peter Benie for spotting this.
 */
static inline void cap_emulate_setxuid (int old_ruid, int old_euid,
					int old_suid)
{
	if ((old_ruid == 0 || old_euid == 0 || old_suid == 0) &&
	    (current->uid != 0 && current->euid != 0 && current->suid != 0) &&
	    !current->keep_capabilities) {
		cap_clear (current->cap_permitted);
		cap_clear (current->cap_effective);
	}
	if (old_euid == 0 && current->euid != 0) {
		cap_clear (current->cap_effective);
	}
	if (old_euid != 0 && current->euid == 0) {
		current->cap_effective = current->cap_permitted;
	}
}

int cap_task_post_setuid (uid_t old_ruid, uid_t old_euid, uid_t old_suid,
			  int flags)
{
	switch (flags) {
	case LSM_SETID_RE:
	case LSM_SETID_ID:
	case LSM_SETID_RES:
		/* Copied from kernel/sys.c:setreuid/setuid/setresuid. */
		if (!issecure (SECURE_NO_SETUID_FIXUP)) {
			cap_emulate_setxuid (old_ruid, old_euid, old_suid);
		}
		break;
	case LSM_SETID_FS:
		{
			uid_t old_fsuid = old_ruid;

			/* Copied from kernel/sys.c:setfsuid. */

			/*
			 * FIXME - is fsuser used for all CAP_FS_MASK capabilities?
			 *          if not, we might be a bit too harsh here.
			 */

			if (!issecure (SECURE_NO_SETUID_FIXUP)) {
				if (old_fsuid == 0 && current->fsuid != 0) {
					cap_t (current->cap_effective) &=
					    ~CAP_FS_MASK;
				}
				if (old_fsuid != 0 && current->fsuid == 0) {
					cap_t (current->cap_effective) |=
					    (cap_t (current->cap_permitted) &
					     CAP_FS_MASK);
				}
			}
			break;
		}
	default:
		return -EINVAL;
	}

	return 0;
}

void cap_task_reparent_to_init (struct task_struct *p)
{
	p->cap_effective = CAP_INIT_EFF_SET;
	p->cap_inheritable = CAP_INIT_INH_SET;
	p->cap_permitted = CAP_FULL_SET;
	p->keep_capabilities = 0;
	return;
}

int cap_syslog (int type)
{
	if ((type != 3 && type != 10) && !capable(CAP_SYS_ADMIN))
		return -EPERM;
	return 0;
}

int cap_vm_enough_memory(long pages)
{
	int cap_sys_admin = 0;

	if (cap_capable(current, CAP_SYS_ADMIN) == 0)
		cap_sys_admin = 1;
	return __vm_enough_memory(pages, cap_sys_admin);
}

EXPORT_SYMBOL(cap_capable);
EXPORT_SYMBOL(cap_settime);
EXPORT_SYMBOL(cap_ptrace);
EXPORT_SYMBOL(cap_capget);
EXPORT_SYMBOL(cap_capset_check);
EXPORT_SYMBOL(cap_capset_set);
EXPORT_SYMBOL(cap_bprm_set_security);
EXPORT_SYMBOL(cap_bprm_apply_creds);
EXPORT_SYMBOL(cap_bprm_secureexec);
EXPORT_SYMBOL(cap_inode_setxattr);
EXPORT_SYMBOL(cap_inode_removexattr);
EXPORT_SYMBOL(cap_task_post_setuid);
EXPORT_SYMBOL(cap_task_reparent_to_init);
EXPORT_SYMBOL(cap_syslog);
EXPORT_SYMBOL(cap_vm_enough_memory);

MODULE_DESCRIPTION("Standard Linux Common Capabilities Security Module");
MODULE_LICENSE("GPL");