projects/linux·blob v4.13 · refs

255 lines · 5.7 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#include <linux/capability.h>
15#include <linux/list.h>
16#include <linux/eventpoll.h>
17#include <linux/file.h>
18
19#include <asm/unistd.h>
20
21/*
22 * We don't expose the real in-memory order of objects for security reasons.
23 * But still the comparison results should be suitable for sorting. So we
24 * obfuscate kernel pointers values and compare the production instead.
25 *
26 * The obfuscation is done in two steps. First we xor the kernel pointer with
27 * a random value, which puts pointer into a new position in a reordered space.
28 * Secondly we multiply the xor production with a large odd random number to
29 * permute its bits even more (the odd multiplier guarantees that the product
30 * is unique ever after the high bits are truncated, since any odd number is
31 * relative prime to 2^n).
32 *
33 * Note also that the obfuscation itself is invisible to userspace and if needed
34 * it can be changed to an alternate scheme.
35 */
36static unsigned long cookies[KCMP_TYPES][2] __read_mostly;
37
38static long kptr_obfuscate(long v, int type)
39{
40 return (v ^ cookies[type][0]) * cookies[type][1];
41}
42
43/*
44 * 0 - equal, i.e. v1 = v2
45 * 1 - less than, i.e. v1 < v2
46 * 2 - greater than, i.e. v1 > v2
47 * 3 - not equal but ordering unavailable (reserved for future)
48 */
49static int kcmp_ptr(void *v1, void *v2, enum kcmp_type type)
50{
51 long t1, t2;
52
53 t1 = kptr_obfuscate((long)v1, type);
54 t2 = kptr_obfuscate((long)v2, type);
55
56 return (t1 < t2) | ((t1 > t2) << 1);
57}
58
59/* The caller must have pinned the task */
60static struct file *
61get_file_raw_ptr(struct task_struct *task, unsigned int idx)
62{
63 struct file *file = NULL;
64
65 task_lock(task);
66 rcu_read_lock();
67
68 if (task->files)
69 file = fcheck_files(task->files, idx);
70
71 rcu_read_unlock();
72 task_unlock(task);
73
74 return file;
75}
76
77static void kcmp_unlock(struct mutex *m1, struct mutex *m2)
78{
79 if (likely(m2 != m1))
80 mutex_unlock(m2);
81 mutex_unlock(m1);
82}
83
84static int kcmp_lock(struct mutex *m1, struct mutex *m2)
85{
86 int err;
87
88 if (m2 > m1)
89 swap(m1, m2);
90
91 err = mutex_lock_killable(m1);
92 if (!err && likely(m1 != m2)) {
93 err = mutex_lock_killable_nested(m2, SINGLE_DEPTH_NESTING);
94 if (err)
95 mutex_unlock(m1);
96 }
97
98 return err;
99}
100
101#ifdef CONFIG_EPOLL
102static int kcmp_epoll_target(struct task_struct *task1,
103 struct task_struct *task2,
104 unsigned long idx1,
105 struct kcmp_epoll_slot __user *uslot)
106{
107 struct file *filp, *filp_epoll, *filp_tgt;
108 struct kcmp_epoll_slot slot;
109 struct files_struct *files;
110
111 if (copy_from_user(&slot, uslot, sizeof(slot)))
112 return -EFAULT;
113
114 filp = get_file_raw_ptr(task1, idx1);
115 if (!filp)
116 return -EBADF;
117
118 files = get_files_struct(task2);
119 if (!files)
120 return -EBADF;
121
122 spin_lock(&files->file_lock);
123 filp_epoll = fcheck_files(files, slot.efd);
124 if (filp_epoll)
125 get_file(filp_epoll);
126 else
127 filp_tgt = ERR_PTR(-EBADF);
128 spin_unlock(&files->file_lock);
129 put_files_struct(files);
130
131 if (filp_epoll) {
132 filp_tgt = get_epoll_tfile_raw_ptr(filp_epoll, slot.tfd, slot.toff);
133 fput(filp_epoll);
134 } else
135
136 if (IS_ERR(filp_tgt))
137 return PTR_ERR(filp_tgt);
138
139 return kcmp_ptr(filp, filp_tgt, KCMP_FILE);
140}
141#else
142static int kcmp_epoll_target(struct task_struct *task1,
143 struct task_struct *task2,
144 unsigned long idx1,
145 struct kcmp_epoll_slot __user *uslot)
146{
147 return -EOPNOTSUPP;
148}
149#endif
150
151SYSCALL_DEFINE5(kcmp, pid_t, pid1, pid_t, pid2, int, type,
152 unsigned long, idx1, unsigned long, idx2)
153{
154 struct task_struct *task1, *task2;
155 int ret;
156
157 rcu_read_lock();
158
159 /*
160 * Tasks are looked up in caller's PID namespace only.
161 */
162 task1 = find_task_by_vpid(pid1);
163 task2 = find_task_by_vpid(pid2);
164 if (!task1 || !task2)
165 goto err_no_task;
166
167 get_task_struct(task1);
168 get_task_struct(task2);
169
170 rcu_read_unlock();
171
172 /*
173 * One should have enough rights to inspect task details.
174 */
175 ret = kcmp_lock(&task1->signal->cred_guard_mutex,
176 &task2->signal->cred_guard_mutex);
177 if (ret)
178 goto err;
179 if (!ptrace_may_access(task1, PTRACE_MODE_READ_REALCREDS) ||
180 !ptrace_may_access(task2, PTRACE_MODE_READ_REALCREDS)) {
181 ret = -EPERM;
182 goto err_unlock;
183 }
184
185 switch (type) {
186 case KCMP_FILE: {
187 struct file *filp1, *filp2;
188
189 filp1 = get_file_raw_ptr(task1, idx1);
190 filp2 = get_file_raw_ptr(task2, idx2);
191
192 if (filp1 && filp2)
193 ret = kcmp_ptr(filp1, filp2, KCMP_FILE);
194 else
195 ret = -EBADF;
196 break;
197 }
198 case KCMP_VM:
199 ret = kcmp_ptr(task1->mm, task2->mm, KCMP_VM);
200 break;
201 case KCMP_FILES:
202 ret = kcmp_ptr(task1->files, task2->files, KCMP_FILES);
203 break;
204 case KCMP_FS:
205 ret = kcmp_ptr(task1->fs, task2->fs, KCMP_FS);
206 break;
207 case KCMP_SIGHAND:
208 ret = kcmp_ptr(task1->sighand, task2->sighand, KCMP_SIGHAND);
209 break;
210 case KCMP_IO:
211 ret = kcmp_ptr(task1->io_context, task2->io_context, KCMP_IO);
212 break;
213 case KCMP_SYSVSEM:
214#ifdef CONFIG_SYSVIPC
215 ret = kcmp_ptr(task1->sysvsem.undo_list,
216 task2->sysvsem.undo_list,
217 KCMP_SYSVSEM);
218#else
219 ret = -EOPNOTSUPP;
220#endif
221 break;
222 case KCMP_EPOLL_TFD:
223 ret = kcmp_epoll_target(task1, task2, idx1, (void *)idx2);
224 break;
225 default:
226 ret = -EINVAL;
227 break;
228 }
229
230err_unlock:
231 kcmp_unlock(&task1->signal->cred_guard_mutex,
232 &task2->signal->cred_guard_mutex);
233err:
234 put_task_struct(task1);
235 put_task_struct(task2);
236
237 return ret;
238
239err_no_task:
240 rcu_read_unlock();
241 return -ESRCH;
242}
243
244static __init int kcmp_cookies_init(void)
245{
246 int i;
247
248 get_random_bytes(cookies, sizeof(cookies));
249
250 for (i = 0; i < KCMP_TYPES; i++)
251 cookies[i][1] |= (~(~0UL >> 1) | 1);
252
253 return 0;
254}
255arch_initcall(kcmp_cookies_init);