1// SPDX-License-Identifier: GPL-2.0
2/*
3 * Creating audit events from TTY input.
4 *
5 * Copyright (C) 2007 Red Hat, Inc.  All rights reserved.
6 *
7 * Authors: Miloslav Trmac <mitr@redhat.com>
8 */
9
10#include <linux/audit.h>
11#include <linux/slab.h>
12#include <linux/tty.h>
13#include "tty.h"
14
15struct tty_audit_buf {
16	struct mutex mutex;	/* Protects all data below */
17	dev_t dev;		/* The TTY which the data is from */
18	unsigned icanon:1;
19	size_t valid;
20	unsigned char *data;	/* Allocated size N_TTY_BUF_SIZE */
21};
22
23static struct tty_audit_buf *tty_audit_buf_ref(void)
24{
25	struct tty_audit_buf *buf;
26
27	buf = current->signal->tty_audit_buf;
28	WARN_ON(buf == ERR_PTR(-ESRCH));
29	return buf;
30}
31
32static struct tty_audit_buf *tty_audit_buf_alloc(void)
33{
34	struct tty_audit_buf *buf;
35
36	buf = kmalloc(sizeof(*buf), GFP_KERNEL);
37	if (!buf)
38		goto err;
39	buf->data = kmalloc(N_TTY_BUF_SIZE, GFP_KERNEL);
40	if (!buf->data)
41		goto err_buf;
42	mutex_init(&buf->mutex);
43	buf->dev = MKDEV(0, 0);
44	buf->icanon = 0;
45	buf->valid = 0;
46	return buf;
47
48err_buf:
49	kfree(buf);
50err:
51	return NULL;
52}
53
54static void tty_audit_buf_free(struct tty_audit_buf *buf)
55{
56	WARN_ON(buf->valid != 0);
57	kfree(buf->data);
58	kfree(buf);
59}
60
61static void tty_audit_log(const char *description, dev_t dev,
62			  unsigned char *data, size_t size)
63{
64	struct audit_buffer *ab;
65	pid_t pid = task_pid_nr(current);
66	uid_t uid = from_kuid(&init_user_ns, task_uid(current));
67	uid_t loginuid = from_kuid(&init_user_ns, audit_get_loginuid(current));
68	unsigned int sessionid = audit_get_sessionid(current);
69
70	ab = audit_log_start(audit_context(), GFP_KERNEL, AUDIT_TTY);
71	if (ab) {
72		char name[sizeof(current->comm)];
73
74		audit_log_format(ab, "%s pid=%u uid=%u auid=%u ses=%u major=%d"
75				 " minor=%d comm=", description, pid, uid,
76				 loginuid, sessionid, MAJOR(dev), MINOR(dev));
77		get_task_comm(name, current);
78		audit_log_untrustedstring(ab, name);
79		audit_log_format(ab, " data=");
80		audit_log_n_hex(ab, data, size);
81		audit_log_end(ab);
82	}
83}
84
85/**
86 *	tty_audit_buf_push	-	Push buffered data out
87 *
88 *	Generate an audit message from the contents of @buf, which is owned by
89 *	the current task.  @buf->mutex must be locked.
90 */
91static void tty_audit_buf_push(struct tty_audit_buf *buf)
92{
93	if (buf->valid == 0)
94		return;
95	if (audit_enabled == AUDIT_OFF) {
96		buf->valid = 0;
97		return;
98	}
99	tty_audit_log("tty", buf->dev, buf->data, buf->valid);
100	buf->valid = 0;
101}
102
103/**
104 *	tty_audit_exit	-	Handle a task exit
105 *
106 *	Make sure all buffered data is written out and deallocate the buffer.
107 *	Only needs to be called if current->signal->tty_audit_buf != %NULL.
108 *
109 *	The process is single-threaded at this point; no other threads share
110 *	current->signal.
111 */
112void tty_audit_exit(void)
113{
114	struct tty_audit_buf *buf;
115
116	buf = xchg(&current->signal->tty_audit_buf, ERR_PTR(-ESRCH));
117	if (!buf)
118		return;
119
120	tty_audit_buf_push(buf);
121	tty_audit_buf_free(buf);
122}
123
124/**
125 *	tty_audit_fork	-	Copy TTY audit state for a new task
126 *
127 *	Set up TTY audit state in @sig from current.  @sig needs no locking.
128 */
129void tty_audit_fork(struct signal_struct *sig)
130{
131	sig->audit_tty = current->signal->audit_tty;
132}
133
134/**
135 *	tty_audit_tiocsti	-	Log TIOCSTI
136 */
137void tty_audit_tiocsti(struct tty_struct *tty, char ch)
138{
139	dev_t dev;
140
141	dev = MKDEV(tty->driver->major, tty->driver->minor_start) + tty->index;
142	if (tty_audit_push())
143		return;
144
145	if (audit_enabled)
146		tty_audit_log("ioctl=TIOCSTI", dev, &ch, 1);
147}
148
149/**
150 *	tty_audit_push	-	Flush current's pending audit data
151 *
152 *	Returns 0 if success, -EPERM if tty audit is disabled
153 */
154int tty_audit_push(void)
155{
156	struct tty_audit_buf *buf;
157
158	if (~current->signal->audit_tty & AUDIT_TTY_ENABLE)
159		return -EPERM;
160
161	buf = tty_audit_buf_ref();
162	if (!IS_ERR_OR_NULL(buf)) {
163		mutex_lock(&buf->mutex);
164		tty_audit_buf_push(buf);
165		mutex_unlock(&buf->mutex);
166	}
167	return 0;
168}
169
170/**
171 *	tty_audit_buf_get	-	Get an audit buffer.
172 *
173 *	Get an audit buffer, allocate it if necessary.  Return %NULL
174 *	if out of memory or ERR_PTR(-ESRCH) if tty_audit_exit() has already
175 *	occurred.  Otherwise, return a new reference to the buffer.
176 */
177static struct tty_audit_buf *tty_audit_buf_get(void)
178{
179	struct tty_audit_buf *buf;
180
181	buf = tty_audit_buf_ref();
182	if (buf)
183		return buf;
184
185	buf = tty_audit_buf_alloc();
186	if (buf == NULL) {
187		audit_log_lost("out of memory in TTY auditing");
188		return NULL;
189	}
190
191	/* Race to use this buffer, free it if another wins */
192	if (cmpxchg(&current->signal->tty_audit_buf, NULL, buf) != NULL)
193		tty_audit_buf_free(buf);
194	return tty_audit_buf_ref();
195}
196
197/**
198 *	tty_audit_add_data	-	Add data for TTY auditing.
199 *
200 *	Audit @data of @size from @tty, if necessary.
201 */
202void tty_audit_add_data(struct tty_struct *tty, const void *data, size_t size)
203{
204	struct tty_audit_buf *buf;
205	unsigned int icanon = !!L_ICANON(tty);
206	unsigned int audit_tty;
207	dev_t dev;
208
209	audit_tty = READ_ONCE(current->signal->audit_tty);
210	if (~audit_tty & AUDIT_TTY_ENABLE)
211		return;
212
213	if (unlikely(size == 0))
214		return;
215
216	if (tty->driver->type == TTY_DRIVER_TYPE_PTY
217	    && tty->driver->subtype == PTY_TYPE_MASTER)
218		return;
219
220	if ((~audit_tty & AUDIT_TTY_LOG_PASSWD) && icanon && !L_ECHO(tty))
221		return;
222
223	buf = tty_audit_buf_get();
224	if (IS_ERR_OR_NULL(buf))
225		return;
226
227	mutex_lock(&buf->mutex);
228	dev = MKDEV(tty->driver->major, tty->driver->minor_start) + tty->index;
229	if (buf->dev != dev || buf->icanon != icanon) {
230		tty_audit_buf_push(buf);
231		buf->dev = dev;
232		buf->icanon = icanon;
233	}
234	do {
235		size_t run;
236
237		run = N_TTY_BUF_SIZE - buf->valid;
238		if (run > size)
239			run = size;
240		memcpy(buf->data + buf->valid, data, run);
241		buf->valid += run;
242		data += run;
243		size -= run;
244		if (buf->valid == N_TTY_BUF_SIZE)
245			tty_audit_buf_push(buf);
246	} while (size != 0);
247	mutex_unlock(&buf->mutex);
248}
249