projects/linux·blob v3.9-rc1 · refs

197 lines · 4.3 KiB

1#include <linux/kernel.h>
2#include <linux/syscalls.h>
3#include <linux/fdtable.h>
4#include <linux/string.h>
5#include <linux/random.h>
6#include <linux/module.h>
7#include <linux/ptrace.h>
8#include <linux/init.h>
9#include <linux/errno.h>
10#include <linux/cache.h>
11#include <linux/bug.h>
12#include <linux/err.h>
13#include <linux/kcmp.h>
14
15#include <asm/unistd.h>
16
17/*
18 * We don't expose the real in-memory order of objects for security reasons.
19 * But still the comparison results should be suitable for sorting. So we
20 * obfuscate kernel pointers values and compare the production instead.
21 *
22 * The obfuscation is done in two steps. First we xor the kernel pointer with
23 * a random value, which puts pointer into a new position in a reordered space.
24 * Secondly we multiply the xor production with a large odd random number to
25 * permute its bits even more (the odd multiplier guarantees that the product
26 * is unique ever after the high bits are truncated, since any odd number is
27 * relative prime to 2^n).
28 *
29 * Note also that the obfuscation itself is invisible to userspace and if needed
30 * it can be changed to an alternate scheme.
31 */
32static unsigned long cookies[KCMP_TYPES][2] __read_mostly;
33
34static long kptr_obfuscate(long v, int type)
35{
36 return (v ^ cookies[type][0]) * cookies[type][1];
37}
38
39/*
40 * 0 - equal, i.e. v1 = v2
41 * 1 - less than, i.e. v1 < v2
42 * 2 - greater than, i.e. v1 > v2
43 * 3 - not equal but ordering unavailable (reserved for future)
44 */
45static int kcmp_ptr(void *v1, void *v2, enum kcmp_type type)
46{
47 long ret;
48
49 ret = kptr_obfuscate((long)v1, type) - kptr_obfuscate((long)v2, type);
50
51 return (ret < 0) | ((ret > 0) << 1);
52}
53
54/* The caller must have pinned the task */
55static struct file *
56get_file_raw_ptr(struct task_struct *task, unsigned int idx)
57{
58 struct file *file = NULL;
59
60 task_lock(task);
61 rcu_read_lock();
62
63 if (task->files)
64 file = fcheck_files(task->files, idx);
65
66 rcu_read_unlock();
67 task_unlock(task);
68
69 return file;
70}
71
72static void kcmp_unlock(struct mutex *m1, struct mutex *m2)
73{
74 if (likely(m2 != m1))
75 mutex_unlock(m2);
76 mutex_unlock(m1);
77}
78
79static int kcmp_lock(struct mutex *m1, struct mutex *m2)
80{
81 int err;
82
83 if (m2 > m1)
84 swap(m1, m2);
85
86 err = mutex_lock_killable(m1);
87 if (!err && likely(m1 != m2)) {
88 err = mutex_lock_killable_nested(m2, SINGLE_DEPTH_NESTING);
89 if (err)
90 mutex_unlock(m1);
91 }
92
93 return err;
94}
95
96SYSCALL_DEFINE5(kcmp, pid_t, pid1, pid_t, pid2, int, type,
97 unsigned long, idx1, unsigned long, idx2)
98{
99 struct task_struct *task1, *task2;
100 int ret;
101
102 rcu_read_lock();
103
104 /*
105 * Tasks are looked up in caller's PID namespace only.
106 */
107 task1 = find_task_by_vpid(pid1);
108 task2 = find_task_by_vpid(pid2);
109 if (!task1 || !task2)
110 goto err_no_task;
111
112 get_task_struct(task1);
113 get_task_struct(task2);
114
115 rcu_read_unlock();
116
117 /*
118 * One should have enough rights to inspect task details.
119 */
120 ret = kcmp_lock(&task1->signal->cred_guard_mutex,
121 &task2->signal->cred_guard_mutex);
122 if (ret)
123 goto err;
124 if (!ptrace_may_access(task1, PTRACE_MODE_READ) ||
125 !ptrace_may_access(task2, PTRACE_MODE_READ)) {
126 ret = -EPERM;
127 goto err_unlock;
128 }
129
130 switch (type) {
131 case KCMP_FILE: {
132 struct file *filp1, *filp2;
133
134 filp1 = get_file_raw_ptr(task1, idx1);
135 filp2 = get_file_raw_ptr(task2, idx2);
136
137 if (filp1 && filp2)
138 ret = kcmp_ptr(filp1, filp2, KCMP_FILE);
139 else
140 ret = -EBADF;
141 break;
142 }
143 case KCMP_VM:
144 ret = kcmp_ptr(task1->mm, task2->mm, KCMP_VM);
145 break;
146 case KCMP_FILES:
147 ret = kcmp_ptr(task1->files, task2->files, KCMP_FILES);
148 break;
149 case KCMP_FS:
150 ret = kcmp_ptr(task1->fs, task2->fs, KCMP_FS);
151 break;
152 case KCMP_SIGHAND:
153 ret = kcmp_ptr(task1->sighand, task2->sighand, KCMP_SIGHAND);
154 break;
155 case KCMP_IO:
156 ret = kcmp_ptr(task1->io_context, task2->io_context, KCMP_IO);
157 break;
158 case KCMP_SYSVSEM:
159#ifdef CONFIG_SYSVIPC
160 ret = kcmp_ptr(task1->sysvsem.undo_list,
161 task2->sysvsem.undo_list,
162 KCMP_SYSVSEM);
163#else
164 ret = -EOPNOTSUPP;
165#endif
166 break;
167 default:
168 ret = -EINVAL;
169 break;
170 }
171
172err_unlock:
173 kcmp_unlock(&task1->signal->cred_guard_mutex,
174 &task2->signal->cred_guard_mutex);
175err:
176 put_task_struct(task1);
177 put_task_struct(task2);
178
179 return ret;
180
181err_no_task:
182 rcu_read_unlock();
183 return -ESRCH;
184}
185
186static __init int kcmp_cookies_init(void)
187{
188 int i;
189
190 get_random_bytes(cookies, sizeof(cookies));
191
192 for (i = 0; i < KCMP_TYPES; i++)
193 cookies[i][1] |= (~(~0UL >> 1) | 1);
194
195 return 0;
196}
197arch_initcall(kcmp_cookies_init);