tty_audit.c

  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
 15#define TTY_AUDIT_BUF_SIZE	4096
 16
 17struct tty_audit_buf {
 18	struct mutex mutex;	/* Protects all data below */
 19	dev_t dev;		/* The TTY which the data is from */
 20	bool icanon;
 21	size_t valid;
 22	u8 *data;		/* Allocated size TTY_AUDIT_BUF_SIZE */
 23};
 24
 25static struct tty_audit_buf *tty_audit_buf_ref(void)
 26{
 27	struct tty_audit_buf *buf;
 28
 29	buf = current->signal->tty_audit_buf;
 30	WARN_ON(buf == ERR_PTR(-ESRCH));
 31	return buf;
 32}
 33
 34static struct tty_audit_buf *tty_audit_buf_alloc(void)
 35{
 36	struct tty_audit_buf *buf;
 37
 38	buf = kzalloc(sizeof(*buf), GFP_KERNEL);
 39	if (!buf)
 40		goto err;
 41
 42	buf->data = kmalloc(TTY_AUDIT_BUF_SIZE, GFP_KERNEL);
 43	if (!buf->data)
 44		goto err_buf;
 45
 46	mutex_init(&buf->mutex);
 47
 48	return buf;
 49
 50err_buf:
 51	kfree(buf);
 52err:
 53	return NULL;
 54}
 55
 56static void tty_audit_buf_free(struct tty_audit_buf *buf)
 57{
 58	WARN_ON(buf->valid != 0);
 59	kfree(buf->data);
 60	kfree(buf);
 61}
 62
 63static void tty_audit_log(const char *description, dev_t dev,
 64			  const u8 *data, size_t size)
 65{
 66	struct audit_buffer *ab;
 67	pid_t pid = task_pid_nr(current);
 68	uid_t uid = from_kuid(&init_user_ns, task_uid(current));
 69	uid_t loginuid = from_kuid(&init_user_ns, audit_get_loginuid(current));
 70	unsigned int sessionid = audit_get_sessionid(current);
 71	char name[TASK_COMM_LEN];
 72
 73	ab = audit_log_start(audit_context(), GFP_KERNEL, AUDIT_TTY);
 74	if (!ab)
 75		return;
 76
 77	audit_log_format(ab, "%s pid=%u uid=%u auid=%u ses=%u major=%d minor=%d comm=",
 78			 description, pid, uid, loginuid, sessionid,
 79			 MAJOR(dev), MINOR(dev));
 80	get_task_comm(name, current);
 81	audit_log_untrustedstring(ab, name);
 82	audit_log_format(ab, " data=");
 83	audit_log_n_hex(ab, data, size);
 84	audit_log_end(ab);
 85}
 86
 87/*
 88 *	tty_audit_buf_push	-	Push buffered data out
 89 *
 90 *	Generate an audit message from the contents of @buf, which is owned by
 91 *	the current task.  @buf->mutex must be locked.
 92 */
 93static void tty_audit_buf_push(struct tty_audit_buf *buf)
 94{
 95	if (buf->valid == 0)
 96		return;
 97	if (audit_enabled == AUDIT_OFF) {
 98		buf->valid = 0;
 99		return;
100	}
101	tty_audit_log("tty", buf->dev, buf->data, buf->valid);
102	buf->valid = 0;
103}
104
105/**
106 *	tty_audit_exit	-	Handle a task exit
107 *
108 *	Make sure all buffered data is written out and deallocate the buffer.
109 *	Only needs to be called if current->signal->tty_audit_buf != %NULL.
110 *
111 *	The process is single-threaded at this point; no other threads share
112 *	current->signal.
113 */
114void tty_audit_exit(void)
115{
116	struct tty_audit_buf *buf;
117
118	buf = xchg(&current->signal->tty_audit_buf, ERR_PTR(-ESRCH));
119	if (!buf)
120		return;
121
122	tty_audit_buf_push(buf);
123	tty_audit_buf_free(buf);
124}
125
126/*
127 *	tty_audit_fork	-	Copy TTY audit state for a new task
128 *
129 *	Set up TTY audit state in @sig from current.  @sig needs no locking.
130 */
131void tty_audit_fork(struct signal_struct *sig)
132{
133	sig->audit_tty = current->signal->audit_tty;
134}
135
136/*
137 *	tty_audit_tiocsti	-	Log TIOCSTI
138 */
139void tty_audit_tiocsti(const struct tty_struct *tty, u8 ch)
140{
141	dev_t dev;
142
143	dev = MKDEV(tty->driver->major, tty->driver->minor_start) + tty->index;
144	if (tty_audit_push())
145		return;
146
147	if (audit_enabled)
148		tty_audit_log("ioctl=TIOCSTI", dev, &ch, 1);
149}
150
151/*
152 *	tty_audit_push	-	Flush current's pending audit data
153 *
154 *	Returns 0 if success, -EPERM if tty audit is disabled
155 */
156int tty_audit_push(void)
157{
158	struct tty_audit_buf *buf;
159
160	if (~current->signal->audit_tty & AUDIT_TTY_ENABLE)
161		return -EPERM;
162
163	buf = tty_audit_buf_ref();
164	if (!IS_ERR_OR_NULL(buf)) {
165		mutex_lock(&buf->mutex);
166		tty_audit_buf_push(buf);
167		mutex_unlock(&buf->mutex);
168	}
169	return 0;
170}
171
172/*
173 *	tty_audit_buf_get	-	Get an audit buffer.
174 *
175 *	Get an audit buffer, allocate it if necessary.  Return %NULL
176 *	if out of memory or ERR_PTR(-ESRCH) if tty_audit_exit() has already
177 *	occurred.  Otherwise, return a new reference to the buffer.
178 */
179static struct tty_audit_buf *tty_audit_buf_get(void)
180{
181	struct tty_audit_buf *buf;
182
183	buf = tty_audit_buf_ref();
184	if (buf)
185		return buf;
186
187	buf = tty_audit_buf_alloc();
188	if (buf == NULL) {
189		audit_log_lost("out of memory in TTY auditing");
190		return NULL;
191	}
192
193	/* Race to use this buffer, free it if another wins */
194	if (cmpxchg(&current->signal->tty_audit_buf, NULL, buf) != NULL)
195		tty_audit_buf_free(buf);
196	return tty_audit_buf_ref();
197}
198
199/*
200 *	tty_audit_add_data	-	Add data for TTY auditing.
201 *
202 *	Audit @data of @size from @tty, if necessary.
203 */
204void tty_audit_add_data(const struct tty_struct *tty, const void *data,
205			size_t size)
206{
207	struct tty_audit_buf *buf;
208	unsigned int audit_tty;
209	bool icanon = L_ICANON(tty);
210	dev_t dev;
211
212	audit_tty = READ_ONCE(current->signal->audit_tty);
213	if (~audit_tty & AUDIT_TTY_ENABLE)
214		return;
215
216	if (unlikely(size == 0))
217		return;
218
219	if (tty->driver->type == TTY_DRIVER_TYPE_PTY
220	    && tty->driver->subtype == PTY_TYPE_MASTER)
221		return;
222
223	if ((~audit_tty & AUDIT_TTY_LOG_PASSWD) && icanon && !L_ECHO(tty))
224		return;
225
226	buf = tty_audit_buf_get();
227	if (IS_ERR_OR_NULL(buf))
228		return;
229
230	mutex_lock(&buf->mutex);
231	dev = MKDEV(tty->driver->major, tty->driver->minor_start) + tty->index;
232	if (buf->dev != dev || buf->icanon != icanon) {
233		tty_audit_buf_push(buf);
234		buf->dev = dev;
235		buf->icanon = icanon;
236	}
237	do {
238		size_t run;
239
240		run = TTY_AUDIT_BUF_SIZE - buf->valid;
241		if (run > size)
242			run = size;
243		memcpy(buf->data + buf->valid, data, run);
244		buf->valid += run;
245		data += run;
246		size -= run;
247		if (buf->valid == TTY_AUDIT_BUF_SIZE)
248			tty_audit_buf_push(buf);
249	} while (size != 0);
250	mutex_unlock(&buf->mutex);
251}