Merge tag 'sound-3.11' of git://git.kernel.org/pub/scm/linux/kernel/git/tiwai/sound
[linux-2.6.git] / kernel / kcmp.c
blobe30ac0fe61c3ded5533cb4db8e95b2d41dcf2ac8
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>
15 #include <asm/unistd.h>
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.
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).
29 * Note also that the obfuscation itself is invisible to userspace and if needed
30 * it can be changed to an alternate scheme.
32 static unsigned long cookies[KCMP_TYPES][2] __read_mostly;
34 static long kptr_obfuscate(long v, int type)
36 return (v ^ cookies[type][0]) * cookies[type][1];
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)
45 static int kcmp_ptr(void *v1, void *v2, enum kcmp_type type)
47 long ret;
49 ret = kptr_obfuscate((long)v1, type) - kptr_obfuscate((long)v2, type);
51 return (ret < 0) | ((ret > 0) << 1);
54 /* The caller must have pinned the task */
55 static struct file *
56 get_file_raw_ptr(struct task_struct *task, unsigned int idx)
58 struct file *file = NULL;
60 task_lock(task);
61 rcu_read_lock();
63 if (task->files)
64 file = fcheck_files(task->files, idx);
66 rcu_read_unlock();
67 task_unlock(task);
69 return file;
72 static void kcmp_unlock(struct mutex *m1, struct mutex *m2)
74 if (likely(m2 != m1))
75 mutex_unlock(m2);
76 mutex_unlock(m1);
79 static int kcmp_lock(struct mutex *m1, struct mutex *m2)
81 int err;
83 if (m2 > m1)
84 swap(m1, m2);
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);
93 return err;
96 SYSCALL_DEFINE5(kcmp, pid_t, pid1, pid_t, pid2, int, type,
97 unsigned long, idx1, unsigned long, idx2)
99 struct task_struct *task1, *task2;
100 int ret;
102 rcu_read_lock();
105 * Tasks are looked up in caller's PID namespace only.
107 task1 = find_task_by_vpid(pid1);
108 task2 = find_task_by_vpid(pid2);
109 if (!task1 || !task2)
110 goto err_no_task;
112 get_task_struct(task1);
113 get_task_struct(task2);
115 rcu_read_unlock();
118 * One should have enough rights to inspect task details.
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;
130 switch (type) {
131 case KCMP_FILE: {
132 struct file *filp1, *filp2;
134 filp1 = get_file_raw_ptr(task1, idx1);
135 filp2 = get_file_raw_ptr(task2, idx2);
137 if (filp1 && filp2)
138 ret = kcmp_ptr(filp1, filp2, KCMP_FILE);
139 else
140 ret = -EBADF;
141 break;
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;
172 err_unlock:
173 kcmp_unlock(&task1->signal->cred_guard_mutex,
174 &task2->signal->cred_guard_mutex);
175 err:
176 put_task_struct(task1);
177 put_task_struct(task2);
179 return ret;
181 err_no_task:
182 rcu_read_unlock();
183 return -ESRCH;
186 static __init int kcmp_cookies_init(void)
188 int i;
190 get_random_bytes(cookies, sizeof(cookies));
192 for (i = 0; i < KCMP_TYPES; i++)
193 cookies[i][1] |= (~(~0UL >> 1) | 1);
195 return 0;
197 arch_initcall(kcmp_cookies_init);