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_fdget_rcu(task, idx);
 68	rcu_read_unlock();
 69	if (file)
 70		fput(file);
 71
 72	return file;
 73}
 74
 75static void kcmp_unlock(struct rw_semaphore *l1, struct rw_semaphore *l2)
 76{
 77	if (likely(l2 != l1))
 78		up_read(l2);
 79	up_read(l1);
 80}
 81
 82static int kcmp_lock(struct rw_semaphore *l1, struct rw_semaphore *l2)
 83{
 84	int err;
 85
 86	if (l2 > l1)
 87		swap(l1, l2);
 88
 89	err = down_read_killable(l1);
 90	if (!err && likely(l1 != l2)) {
 91		err = down_read_killable_nested(l2, SINGLE_DEPTH_NESTING);
 92		if (err)
 93			up_read(l1);
 94	}
 95
 96	return err;
 97}
 98
 99#ifdef CONFIG_EPOLL
100static int kcmp_epoll_target(struct task_struct *task1,
101			     struct task_struct *task2,
102			     unsigned long idx1,
103			     struct kcmp_epoll_slot __user *uslot)
104{
105	struct file *filp, *filp_epoll, *filp_tgt;
106	struct kcmp_epoll_slot slot;
107
108	if (copy_from_user(&slot, uslot, sizeof(slot)))
109		return -EFAULT;
110
111	filp = get_file_raw_ptr(task1, idx1);
112	if (!filp)
113		return -EBADF;
114
115	filp_epoll = fget_task(task2, slot.efd);
116	if (!filp_epoll)
117		return -EBADF;
118
119	filp_tgt = get_epoll_tfile_raw_ptr(filp_epoll, slot.tfd, slot.toff);
120	fput(filp_epoll);
121
122	if (IS_ERR(filp_tgt))
123		return PTR_ERR(filp_tgt);
124
125	return kcmp_ptr(filp, filp_tgt, KCMP_FILE);
126}
127#else
128static int kcmp_epoll_target(struct task_struct *task1,
129			     struct task_struct *task2,
130			     unsigned long idx1,
131			     struct kcmp_epoll_slot __user *uslot)
132{
133	return -EOPNOTSUPP;
134}
135#endif
136
137SYSCALL_DEFINE5(kcmp, pid_t, pid1, pid_t, pid2, int, type,
138		unsigned long, idx1, unsigned long, idx2)
139{
140	struct task_struct *task1, *task2;
141	int ret;
142
143	rcu_read_lock();
144
145	/*
146	 * Tasks are looked up in caller's PID namespace only.
147	 */
148	task1 = find_task_by_vpid(pid1);
149	task2 = find_task_by_vpid(pid2);
150	if (!task1 || !task2)
151		goto err_no_task;
152
153	get_task_struct(task1);
154	get_task_struct(task2);
155
156	rcu_read_unlock();
157
158	/*
159	 * One should have enough rights to inspect task details.
160	 */
161	ret = kcmp_lock(&task1->signal->exec_update_lock,
162			&task2->signal->exec_update_lock);
163	if (ret)
164		goto err;
165	if (!ptrace_may_access(task1, PTRACE_MODE_READ_REALCREDS) ||
166	    !ptrace_may_access(task2, PTRACE_MODE_READ_REALCREDS)) {
167		ret = -EPERM;
168		goto err_unlock;
169	}
170
171	switch (type) {
172	case KCMP_FILE: {
173		struct file *filp1, *filp2;
174
175		filp1 = get_file_raw_ptr(task1, idx1);
176		filp2 = get_file_raw_ptr(task2, idx2);
177
178		if (filp1 && filp2)
179			ret = kcmp_ptr(filp1, filp2, KCMP_FILE);
180		else
181			ret = -EBADF;
182		break;
183	}
184	case KCMP_VM:
185		ret = kcmp_ptr(task1->mm, task2->mm, KCMP_VM);
186		break;
187	case KCMP_FILES:
188		ret = kcmp_ptr(task1->files, task2->files, KCMP_FILES);
189		break;
190	case KCMP_FS:
191		ret = kcmp_ptr(task1->fs, task2->fs, KCMP_FS);
192		break;
193	case KCMP_SIGHAND:
194		ret = kcmp_ptr(task1->sighand, task2->sighand, KCMP_SIGHAND);
195		break;
196	case KCMP_IO:
197		ret = kcmp_ptr(task1->io_context, task2->io_context, KCMP_IO);
198		break;
199	case KCMP_SYSVSEM:
200#ifdef CONFIG_SYSVIPC
201		ret = kcmp_ptr(task1->sysvsem.undo_list,
202			       task2->sysvsem.undo_list,
203			       KCMP_SYSVSEM);
204#else
205		ret = -EOPNOTSUPP;
206#endif
207		break;
208	case KCMP_EPOLL_TFD:
209		ret = kcmp_epoll_target(task1, task2, idx1, (void *)idx2);
210		break;
211	default:
212		ret = -EINVAL;
213		break;
214	}
215
216err_unlock:
217	kcmp_unlock(&task1->signal->exec_update_lock,
218		    &task2->signal->exec_update_lock);
219err:
220	put_task_struct(task1);
221	put_task_struct(task2);
222
223	return ret;
224
225err_no_task:
226	rcu_read_unlock();
227	return -ESRCH;
228}
229
230static __init int kcmp_cookies_init(void)
231{
232	int i;
233
234	get_random_bytes(cookies, sizeof(cookies));
235
236	for (i = 0; i < KCMP_TYPES; i++)
237		cookies[i][1] |= (~(~0UL >>  1) | 1);
238
239	return 0;
240}
241arch_initcall(kcmp_cookies_init);