1// SPDX-License-Identifier: GPL-2.0
  2#include <linux/kernel.h>
  3#include <linux/syscalls.h>
  4#include <linux/fdtable.h>
  5#include <linux/string.h>
  6#include <linux/random.h>
  7#include <linux/module.h>
  8#include <linux/ptrace.h>
  9#include <linux/init.h>
 10#include <linux/errno.h>
 11#include <linux/cache.h>
 12#include <linux/bug.h>
 13#include <linux/err.h>
 14#include <linux/kcmp.h>
 15#include <linux/capability.h>
 16#include <linux/list.h>
 17#include <linux/eventpoll.h>
 18#include <linux/file.h>
 19
 20#include <asm/unistd.h>
 21
 22/*
 23 * We don't expose the real in-memory order of objects for security reasons.
 24 * But still the comparison results should be suitable for sorting. So we
 25 * obfuscate kernel pointers values and compare the production instead.
 26 *
 27 * The obfuscation is done in two steps. First we xor the kernel pointer with
 28 * a random value, which puts pointer into a new position in a reordered space.
 29 * Secondly we multiply the xor production with a large odd random number to
 30 * permute its bits even more (the odd multiplier guarantees that the product
 31 * is unique ever after the high bits are truncated, since any odd number is
 32 * relative prime to 2^n).
 33 *
 34 * Note also that the obfuscation itself is invisible to userspace and if needed
 35 * it can be changed to an alternate scheme.
 36 */
 37static unsigned long cookies[KCMP_TYPES][2] __read_mostly;
 38
 39static long kptr_obfuscate(long v, int type)
 40{
 41	return (v ^ cookies[type][0]) * cookies[type][1];
 42}
 43
 44/*
 45 * 0 - equal, i.e. v1 = v2
 46 * 1 - less than, i.e. v1 < v2
 47 * 2 - greater than, i.e. v1 > v2
 48 * 3 - not equal but ordering unavailable (reserved for future)
 49 */
 50static int kcmp_ptr(void *v1, void *v2, enum kcmp_type type)
 51{
 52	long t1, t2;
 53
 54	t1 = kptr_obfuscate((long)v1, type);
 55	t2 = kptr_obfuscate((long)v2, type);
 56
 57	return (t1 < t2) | ((t1 > t2) << 1);
 58}
 59
 60/* The caller must have pinned the task */
 61static struct file *
 62get_file_raw_ptr(struct task_struct *task, unsigned int idx)
 63{
 64	struct file *file;
 65
 66	rcu_read_lock();
 67	file = task_lookup_fd_rcu(task, idx);
 68	rcu_read_unlock();
 69
 70	return file;
 71}
 72
 73static void kcmp_unlock(struct rw_semaphore *l1, struct rw_semaphore *l2)
 74{
 75	if (likely(l2 != l1))
 76		up_read(l2);
 77	up_read(l1);
 78}
 79
 80static int kcmp_lock(struct rw_semaphore *l1, struct rw_semaphore *l2)
 81{
 82	int err;
 83
 84	if (l2 > l1)
 85		swap(l1, l2);
 86
 87	err = down_read_killable(l1);
 88	if (!err && likely(l1 != l2)) {
 89		err = down_read_killable_nested(l2, SINGLE_DEPTH_NESTING);
 90		if (err)
 91			up_read(l1);
 92	}
 93
 94	return err;
 95}
 96
 97#ifdef CONFIG_EPOLL
 98static int kcmp_epoll_target(struct task_struct *task1,
 99			     struct task_struct *task2,
100			     unsigned long idx1,
101			     struct kcmp_epoll_slot __user *uslot)
102{
103	struct file *filp, *filp_epoll, *filp_tgt;
104	struct kcmp_epoll_slot slot;
105
106	if (copy_from_user(&slot, uslot, sizeof(slot)))
107		return -EFAULT;
108
109	filp = get_file_raw_ptr(task1, idx1);
110	if (!filp)
111		return -EBADF;
112
113	filp_epoll = fget_task(task2, slot.efd);
114	if (!filp_epoll)
115		return -EBADF;
116
117	filp_tgt = get_epoll_tfile_raw_ptr(filp_epoll, slot.tfd, slot.toff);
118	fput(filp_epoll);
119
120	if (IS_ERR(filp_tgt))
121		return PTR_ERR(filp_tgt);
122
123	return kcmp_ptr(filp, filp_tgt, KCMP_FILE);
124}
125#else
126static int kcmp_epoll_target(struct task_struct *task1,
127			     struct task_struct *task2,
128			     unsigned long idx1,
129			     struct kcmp_epoll_slot __user *uslot)
130{
131	return -EOPNOTSUPP;
132}
133#endif
134
135SYSCALL_DEFINE5(kcmp, pid_t, pid1, pid_t, pid2, int, type,
136		unsigned long, idx1, unsigned long, idx2)
137{
138	struct task_struct *task1, *task2;
139	int ret;
140
141	rcu_read_lock();
142
143	/*
144	 * Tasks are looked up in caller's PID namespace only.
145	 */
146	task1 = find_task_by_vpid(pid1);
147	task2 = find_task_by_vpid(pid2);
148	if (!task1 || !task2)
149		goto err_no_task;
150
151	get_task_struct(task1);
152	get_task_struct(task2);
153
154	rcu_read_unlock();
155
156	/*
157	 * One should have enough rights to inspect task details.
158	 */
159	ret = kcmp_lock(&task1->signal->exec_update_lock,
160			&task2->signal->exec_update_lock);
161	if (ret)
162		goto err;
163	if (!ptrace_may_access(task1, PTRACE_MODE_READ_REALCREDS) ||
164	    !ptrace_may_access(task2, PTRACE_MODE_READ_REALCREDS)) {
165		ret = -EPERM;
166		goto err_unlock;
167	}
168
169	switch (type) {
170	case KCMP_FILE: {
171		struct file *filp1, *filp2;
172
173		filp1 = get_file_raw_ptr(task1, idx1);
174		filp2 = get_file_raw_ptr(task2, idx2);
175
176		if (filp1 && filp2)
177			ret = kcmp_ptr(filp1, filp2, KCMP_FILE);
178		else
179			ret = -EBADF;
180		break;
181	}
182	case KCMP_VM:
183		ret = kcmp_ptr(task1->mm, task2->mm, KCMP_VM);
184		break;
185	case KCMP_FILES:
186		ret = kcmp_ptr(task1->files, task2->files, KCMP_FILES);
187		break;
188	case KCMP_FS:
189		ret = kcmp_ptr(task1->fs, task2->fs, KCMP_FS);
190		break;
191	case KCMP_SIGHAND:
192		ret = kcmp_ptr(task1->sighand, task2->sighand, KCMP_SIGHAND);
193		break;
194	case KCMP_IO:
195		ret = kcmp_ptr(task1->io_context, task2->io_context, KCMP_IO);
196		break;
197	case KCMP_SYSVSEM:
198#ifdef CONFIG_SYSVIPC
199		ret = kcmp_ptr(task1->sysvsem.undo_list,
200			       task2->sysvsem.undo_list,
201			       KCMP_SYSVSEM);
202#else
203		ret = -EOPNOTSUPP;
204#endif
205		break;
206	case KCMP_EPOLL_TFD:
207		ret = kcmp_epoll_target(task1, task2, idx1, (void *)idx2);
208		break;
209	default:
210		ret = -EINVAL;
211		break;
212	}
213
214err_unlock:
215	kcmp_unlock(&task1->signal->exec_update_lock,
216		    &task2->signal->exec_update_lock);
217err:
218	put_task_struct(task1);
219	put_task_struct(task2);
220
221	return ret;
222
223err_no_task:
224	rcu_read_unlock();
225	return -ESRCH;
226}
227
228static __init int kcmp_cookies_init(void)
229{
230	int i;
231
232	get_random_bytes(cookies, sizeof(cookies));
233
234	for (i = 0; i < KCMP_TYPES; i++)
235		cookies[i][1] |= (~(~0UL >>  1) | 1);
236
237	return 0;
238}
239arch_initcall(kcmp_cookies_init);

  1// SPDX-License-Identifier: GPL-2.0
  2#include <linux/kernel.h>
  3#include <linux/syscalls.h>
  4#include <linux/fdtable.h>
  5#include <linux/string.h>
  6#include <linux/random.h>
  7#include <linux/module.h>
  8#include <linux/ptrace.h>
  9#include <linux/init.h>
 10#include <linux/errno.h>
 11#include <linux/cache.h>
 12#include <linux/bug.h>
 13#include <linux/err.h>
 14#include <linux/kcmp.h>
 15#include <linux/capability.h>
 16#include <linux/list.h>
 17#include <linux/eventpoll.h>
 18#include <linux/file.h>
 19
 20#include <asm/unistd.h>
 21
 22/*
 23 * We don't expose the real in-memory order of objects for security reasons.
 24 * But still the comparison results should be suitable for sorting. So we
 25 * obfuscate kernel pointers values and compare the production instead.
 26 *
 27 * The obfuscation is done in two steps. First we xor the kernel pointer with
 28 * a random value, which puts pointer into a new position in a reordered space.
 29 * Secondly we multiply the xor production with a large odd random number to
 30 * permute its bits even more (the odd multiplier guarantees that the product
 31 * is unique ever after the high bits are truncated, since any odd number is
 32 * relative prime to 2^n).
 33 *
 34 * Note also that the obfuscation itself is invisible to userspace and if needed
 35 * it can be changed to an alternate scheme.
 36 */
 37static unsigned long cookies[KCMP_TYPES][2] __read_mostly;
 38
 39static long kptr_obfuscate(long v, int type)
 40{
 41	return (v ^ cookies[type][0]) * cookies[type][1];
 42}
 43
 44/*
 45 * 0 - equal, i.e. v1 = v2
 46 * 1 - less than, i.e. v1 < v2
 47 * 2 - greater than, i.e. v1 > v2
 48 * 3 - not equal but ordering unavailable (reserved for future)
 49 */
 50static int kcmp_ptr(void *v1, void *v2, enum kcmp_type type)
 51{
 52	long t1, t2;
 53
 54	t1 = kptr_obfuscate((long)v1, type);
 55	t2 = kptr_obfuscate((long)v2, type);
 56
 57	return (t1 < t2) | ((t1 > t2) << 1);
 58}
 59
 60/* The caller must have pinned the task */
 61static struct file *
 62get_file_raw_ptr(struct task_struct *task, unsigned int idx)
 63{
 64	struct file *file;
 65
 66	file = fget_task(task, idx);
 67	if (file)
 68		fput(file);
 69
 70	return file;
 71}
 72
 73static void kcmp_unlock(struct rw_semaphore *l1, struct rw_semaphore *l2)
 74{
 75	if (likely(l2 != l1))
 76		up_read(l2);
 77	up_read(l1);
 78}
 79
 80static int kcmp_lock(struct rw_semaphore *l1, struct rw_semaphore *l2)
 81{
 82	int err;
 83
 84	if (l2 > l1)
 85		swap(l1, l2);
 86
 87	err = down_read_killable(l1);
 88	if (!err && likely(l1 != l2)) {
 89		err = down_read_killable_nested(l2, SINGLE_DEPTH_NESTING);
 90		if (err)
 91			up_read(l1);
 92	}
 93
 94	return err;
 95}
 96
 97#ifdef CONFIG_EPOLL
 98static int kcmp_epoll_target(struct task_struct *task1,
 99			     struct task_struct *task2,
100			     unsigned long idx1,
101			     struct kcmp_epoll_slot __user *uslot)
102{
103	struct file *filp, *filp_epoll, *filp_tgt;
104	struct kcmp_epoll_slot slot;
105
106	if (copy_from_user(&slot, uslot, sizeof(slot)))
107		return -EFAULT;
108
109	filp = get_file_raw_ptr(task1, idx1);
110	if (!filp)
111		return -EBADF;
112
113	filp_epoll = fget_task(task2, slot.efd);
114	if (!filp_epoll)
115		return -EBADF;
116
117	filp_tgt = get_epoll_tfile_raw_ptr(filp_epoll, slot.tfd, slot.toff);
118	fput(filp_epoll);
119
120	if (IS_ERR(filp_tgt))
121		return PTR_ERR(filp_tgt);
122
123	return kcmp_ptr(filp, filp_tgt, KCMP_FILE);
124}
125#else
126static int kcmp_epoll_target(struct task_struct *task1,
127			     struct task_struct *task2,
128			     unsigned long idx1,
129			     struct kcmp_epoll_slot __user *uslot)
130{
131	return -EOPNOTSUPP;
132}
133#endif
134
135SYSCALL_DEFINE5(kcmp, pid_t, pid1, pid_t, pid2, int, type,
136		unsigned long, idx1, unsigned long, idx2)
137{
138	struct task_struct *task1, *task2;
139	int ret;
140
141	rcu_read_lock();
142
143	/*
144	 * Tasks are looked up in caller's PID namespace only.
145	 */
146	task1 = find_task_by_vpid(pid1);
147	task2 = find_task_by_vpid(pid2);
148	if (!task1 || !task2)
149		goto err_no_task;
150
151	get_task_struct(task1);
152	get_task_struct(task2);
153
154	rcu_read_unlock();
155
156	/*
157	 * One should have enough rights to inspect task details.
158	 */
159	ret = kcmp_lock(&task1->signal->exec_update_lock,
160			&task2->signal->exec_update_lock);
161	if (ret)
162		goto err;
163	if (!ptrace_may_access(task1, PTRACE_MODE_READ_REALCREDS) ||
164	    !ptrace_may_access(task2, PTRACE_MODE_READ_REALCREDS)) {
165		ret = -EPERM;
166		goto err_unlock;
167	}
168
169	switch (type) {
170	case KCMP_FILE: {
171		struct file *filp1, *filp2;
172
173		filp1 = get_file_raw_ptr(task1, idx1);
174		filp2 = get_file_raw_ptr(task2, idx2);
175
176		if (filp1 && filp2)
177			ret = kcmp_ptr(filp1, filp2, KCMP_FILE);
178		else
179			ret = -EBADF;
180		break;
181	}
182	case KCMP_VM:
183		ret = kcmp_ptr(task1->mm, task2->mm, KCMP_VM);
184		break;
185	case KCMP_FILES:
186		ret = kcmp_ptr(task1->files, task2->files, KCMP_FILES);
187		break;
188	case KCMP_FS:
189		ret = kcmp_ptr(task1->fs, task2->fs, KCMP_FS);
190		break;
191	case KCMP_SIGHAND:
192		ret = kcmp_ptr(task1->sighand, task2->sighand, KCMP_SIGHAND);
193		break;
194	case KCMP_IO:
195		ret = kcmp_ptr(task1->io_context, task2->io_context, KCMP_IO);
196		break;
197	case KCMP_SYSVSEM:
198#ifdef CONFIG_SYSVIPC
199		ret = kcmp_ptr(task1->sysvsem.undo_list,
200			       task2->sysvsem.undo_list,
201			       KCMP_SYSVSEM);
202#else
203		ret = -EOPNOTSUPP;
204#endif
205		break;
206	case KCMP_EPOLL_TFD:
207		ret = kcmp_epoll_target(task1, task2, idx1, (void *)idx2);
208		break;
209	default:
210		ret = -EINVAL;
211		break;
212	}
213
214err_unlock:
215	kcmp_unlock(&task1->signal->exec_update_lock,
216		    &task2->signal->exec_update_lock);
217err:
218	put_task_struct(task1);
219	put_task_struct(task2);
220
221	return ret;
222
223err_no_task:
224	rcu_read_unlock();
225	return -ESRCH;
226}
227
228static __init int kcmp_cookies_init(void)
229{
230	int i;
231
232	get_random_bytes(cookies, sizeof(cookies));
233
234	for (i = 0; i < KCMP_TYPES; i++)
235		cookies[i][1] |= (~(~0UL >>  1) | 1);
236
237	return 0;
238}
239arch_initcall(kcmp_cookies_init);