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 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 */
 56static struct file *
 57get_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
 73static 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
 80static 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
 97SYSCALL_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
173err_unlock:
174	kcmp_unlock(&task1->signal->cred_guard_mutex,
175		    &task2->signal->cred_guard_mutex);
176err:
177	put_task_struct(task1);
178	put_task_struct(task2);
179
180	return ret;
181
182err_no_task:
183	rcu_read_unlock();
184	return -ESRCH;
185}
186
187static __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}
198arch_initcall(kcmp_cookies_init);