summaryrefslogtreecommitdiff
path: root/kernel/kcmp.c
blob: 2c596851f8a90c042f3c63b320cc1ec683a5a341 (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
// SPDX-License-Identifier: GPL-2.0
#include <linux/kernel.h>
#include <linux/syscalls.h>
#include <linux/fdtable.h>
#include <linux/string.h>
#include <linux/random.h>
#include <linux/module.h>
#include <linux/ptrace.h>
#include <linux/init.h>
#include <linux/errno.h>
#include <linux/cache.h>
#include <linux/bug.h>
#include <linux/err.h>
#include <linux/kcmp.h>
#include <linux/capability.h>
#include <linux/list.h>
#include <linux/eventpoll.h>
#include <linux/file.h>

#include <asm/unistd.h>

/*
 * We don't expose the real in-memory order of objects for security reasons.
 * But still the comparison results should be suitable for sorting. So we
 * obfuscate kernel pointers values and compare the production instead.
 *
 * The obfuscation is done in two steps. First we xor the kernel pointer with
 * a random value, which puts pointer into a new position in a reordered space.
 * Secondly we multiply the xor production with a large odd random number to
 * permute its bits even more (the odd multiplier guarantees that the product
 * is unique ever after the high bits are truncated, since any odd number is
 * relative prime to 2^n).
 *
 * Note also that the obfuscation itself is invisible to userspace and if needed
 * it can be changed to an alternate scheme.
 */
static unsigned long cookies[KCMP_TYPES][2] __read_mostly;

static long kptr_obfuscate(long v, int type)
{
	return (v ^ cookies[type][0]) * cookies[type][1];
}

/*
 * 0 - equal, i.e. v1 = v2
 * 1 - less than, i.e. v1 < v2
 * 2 - greater than, i.e. v1 > v2
 * 3 - not equal but ordering unavailable (reserved for future)
 */
static int kcmp_ptr(void *v1, void *v2, enum kcmp_type type)
{
	long t1, t2;

	t1 = kptr_obfuscate((long)v1, type);
	t2 = kptr_obfuscate((long)v2, type);

	return (t1 < t2) | ((t1 > t2) << 1);
}

/* The caller must have pinned the task */
static struct file *
get_file_raw_ptr(struct task_struct *task, unsigned int idx)
{
	struct file *file;

	file = fget_task(task, idx);
	if (file)
		fput(file);

	return file;
}

static void kcmp_unlock(struct rw_semaphore *l1, struct rw_semaphore *l2)
{
	if (likely(l2 != l1))
		up_read(l2);
	up_read(l1);
}

static int kcmp_lock(struct rw_semaphore *l1, struct rw_semaphore *l2)
{
	int err;

	if (l2 > l1)
		swap(l1, l2);

	err = down_read_killable(l1);
	if (!err && likely(l1 != l2)) {
		err = down_read_killable_nested(l2, SINGLE_DEPTH_NESTING);
		if (err)
			up_read(l1);
	}

	return err;
}

#ifdef CONFIG_EPOLL
static int kcmp_epoll_target(struct task_struct *task1,
			     struct task_struct *task2,
			     unsigned long idx1,
			     struct kcmp_epoll_slot __user *uslot)
{
	struct file *filp, *filp_epoll, *filp_tgt;
	struct kcmp_epoll_slot slot;

	if (copy_from_user(&slot, uslot, sizeof(slot)))
		return -EFAULT;

	filp = get_file_raw_ptr(task1, idx1);
	if (!filp)
		return -EBADF;

	filp_epoll = fget_task(task2, slot.efd);
	if (!filp_epoll)
		return -EBADF;

	filp_tgt = get_epoll_tfile_raw_ptr(filp_epoll, slot.tfd, slot.toff);
	fput(filp_epoll);

	if (IS_ERR(filp_tgt))
		return PTR_ERR(filp_tgt);

	return kcmp_ptr(filp, filp_tgt, KCMP_FILE);
}
#else
static int kcmp_epoll_target(struct task_struct *task1,
			     struct task_struct *task2,
			     unsigned long idx1,
			     struct kcmp_epoll_slot __user *uslot)
{
	return -EOPNOTSUPP;
}
#endif

SYSCALL_DEFINE5(kcmp, pid_t, pid1, pid_t, pid2, int, type,
		unsigned long, idx1, unsigned long, idx2)
{
	struct task_struct *task1, *task2;
	int ret;

	rcu_read_lock();

	/*
	 * Tasks are looked up in caller's PID namespace only.
	 */
	task1 = find_task_by_vpid(pid1);
	task2 = find_task_by_vpid(pid2);
	if (!task1 || !task2)
		goto err_no_task;

	get_task_struct(task1);
	get_task_struct(task2);

	rcu_read_unlock();

	/*
	 * One should have enough rights to inspect task details.
	 */
	ret = kcmp_lock(&task1->signal->exec_update_lock,
			&task2->signal->exec_update_lock);
	if (ret)
		goto err;
	if (!ptrace_may_access(task1, PTRACE_MODE_READ_REALCREDS) ||
	    !ptrace_may_access(task2, PTRACE_MODE_READ_REALCREDS)) {
		ret = -EPERM;
		goto err_unlock;
	}

	switch (type) {
	case KCMP_FILE: {
		struct file *filp1, *filp2;

		filp1 = get_file_raw_ptr(task1, idx1);
		filp2 = get_file_raw_ptr(task2, idx2);

		if (filp1 && filp2)
			ret = kcmp_ptr(filp1, filp2, KCMP_FILE);
		else
			ret = -EBADF;
		break;
	}
	case KCMP_VM:
		ret = kcmp_ptr(task1->mm, task2->mm, KCMP_VM);
		break;
	case KCMP_FILES:
		ret = kcmp_ptr(task1->files, task2->files, KCMP_FILES);
		break;
	case KCMP_FS:
		ret = kcmp_ptr(task1->fs, task2->fs, KCMP_FS);
		break;
	case KCMP_SIGHAND:
		ret = kcmp_ptr(task1->sighand, task2->sighand, KCMP_SIGHAND);
		break;
	case KCMP_IO:
		ret = kcmp_ptr(task1->io_context, task2->io_context, KCMP_IO);
		break;
	case KCMP_SYSVSEM:
#ifdef CONFIG_SYSVIPC
		ret = kcmp_ptr(task1->sysvsem.undo_list,
			       task2->sysvsem.undo_list,
			       KCMP_SYSVSEM);
#else
		ret = -EOPNOTSUPP;
#endif
		break;
	case KCMP_EPOLL_TFD:
		ret = kcmp_epoll_target(task1, task2, idx1, (void *)idx2);
		break;
	default:
		ret = -EINVAL;
		break;
	}

err_unlock:
	kcmp_unlock(&task1->signal->exec_update_lock,
		    &task2->signal->exec_update_lock);
err:
	put_task_struct(task1);
	put_task_struct(task2);

	return ret;

err_no_task:
	rcu_read_unlock();
	return -ESRCH;
}

static __init int kcmp_cookies_init(void)
{
	int i;

	get_random_bytes(cookies, sizeof(cookies));

	for (i = 0; i < KCMP_TYPES; i++)
		cookies[i][1] |= (~(~0UL >>  1) | 1);

	return 0;
}
arch_initcall(kcmp_cookies_init);