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 */
32 static unsigned long cookies[KCMP_TYPES][2] __read_mostly;
33
kptr_obfuscate(long v,int type)34 static 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 */
kcmp_ptr(void * v1,void * v2,enum kcmp_type type)45 static int kcmp_ptr(void *v1, void *v2, enum kcmp_type type)
46 {
47 long t1, t2;
48
49 t1 = kptr_obfuscate((long)v1, type);
50 t2 = kptr_obfuscate((long)v2, type);
51
52 return (t1 < t2) | ((t1 > t2) << 1);
53 }
54
55 /* The caller must have pinned the task */
56 static struct file *
get_file_raw_ptr(struct task_struct * task,unsigned int idx)57 get_file_raw_ptr(struct task_struct *task, unsigned int idx)
58 {
59 struct file *file = NULL;
60
61 task_lock(task);
62 rcu_read_lock();
63
64 if (task->files)
65 file = fcheck_files(task->files, idx);
66
67 rcu_read_unlock();
68 task_unlock(task);
69
70 return file;
71 }
72
kcmp_unlock(struct mutex * m1,struct mutex * m2)73 static void kcmp_unlock(struct mutex *m1, struct mutex *m2)
74 {
75 if (likely(m2 != m1))
76 mutex_unlock(m2);
77 mutex_unlock(m1);
78 }
79
kcmp_lock(struct mutex * m1,struct mutex * m2)80 static int kcmp_lock(struct mutex *m1, struct mutex *m2)
81 {
82 int err;
83
84 if (m2 > m1)
85 swap(m1, m2);
86
87 err = mutex_lock_killable(m1);
88 if (!err && likely(m1 != m2)) {
89 err = mutex_lock_killable_nested(m2, SINGLE_DEPTH_NESTING);
90 if (err)
91 mutex_unlock(m1);
92 }
93
94 return err;
95 }
96
SYSCALL_DEFINE5(kcmp,pid_t,pid1,pid_t,pid2,int,type,unsigned long,idx1,unsigned long,idx2)97 SYSCALL_DEFINE5(kcmp, pid_t, pid1, pid_t, pid2, int, type,
98 unsigned long, idx1, unsigned long, idx2)
99 {
100 struct task_struct *task1, *task2;
101 int ret;
102
103 rcu_read_lock();
104
105 /*
106 * Tasks are looked up in caller's PID namespace only.
107 */
108 task1 = find_task_by_vpid(pid1);
109 task2 = find_task_by_vpid(pid2);
110 if (!task1 || !task2)
111 goto err_no_task;
112
113 get_task_struct(task1);
114 get_task_struct(task2);
115
116 rcu_read_unlock();
117
118 /*
119 * One should have enough rights to inspect task details.
120 */
121 ret = kcmp_lock(&task1->signal->cred_guard_mutex,
122 &task2->signal->cred_guard_mutex);
123 if (ret)
124 goto err;
125 if (!ptrace_may_access(task1, PTRACE_MODE_READ_REALCREDS) ||
126 !ptrace_may_access(task2, PTRACE_MODE_READ_REALCREDS)) {
127 ret = -EPERM;
128 goto err_unlock;
129 }
130
131 switch (type) {
132 case KCMP_FILE: {
133 struct file *filp1, *filp2;
134
135 filp1 = get_file_raw_ptr(task1, idx1);
136 filp2 = get_file_raw_ptr(task2, idx2);
137
138 if (filp1 && filp2)
139 ret = kcmp_ptr(filp1, filp2, KCMP_FILE);
140 else
141 ret = -EBADF;
142 break;
143 }
144 case KCMP_VM:
145 ret = kcmp_ptr(task1->mm, task2->mm, KCMP_VM);
146 break;
147 case KCMP_FILES:
148 ret = kcmp_ptr(task1->files, task2->files, KCMP_FILES);
149 break;
150 case KCMP_FS:
151 ret = kcmp_ptr(task1->fs, task2->fs, KCMP_FS);
152 break;
153 case KCMP_SIGHAND:
154 ret = kcmp_ptr(task1->sighand, task2->sighand, KCMP_SIGHAND);
155 break;
156 case KCMP_IO:
157 ret = kcmp_ptr(task1->io_context, task2->io_context, KCMP_IO);
158 break;
159 case KCMP_SYSVSEM:
160 #ifdef CONFIG_SYSVIPC
161 ret = kcmp_ptr(task1->sysvsem.undo_list,
162 task2->sysvsem.undo_list,
163 KCMP_SYSVSEM);
164 #else
165 ret = -EOPNOTSUPP;
166 #endif
167 break;
168 default:
169 ret = -EINVAL;
170 break;
171 }
172
173 err_unlock:
174 kcmp_unlock(&task1->signal->cred_guard_mutex,
175 &task2->signal->cred_guard_mutex);
176 err:
177 put_task_struct(task1);
178 put_task_struct(task2);
179
180 return ret;
181
182 err_no_task:
183 rcu_read_unlock();
184 return -ESRCH;
185 }
186
kcmp_cookies_init(void)187 static __init int kcmp_cookies_init(void)
188 {
189 int i;
190
191 get_random_bytes(cookies, sizeof(cookies));
192
193 for (i = 0; i < KCMP_TYPES; i++)
194 cookies[i][1] |= (~(~0UL >> 1) | 1);
195
196 return 0;
197 }
198 arch_initcall(kcmp_cookies_init);
199