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 struct 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 
tty_audit_buf_ref(void)23 static 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 
tty_audit_buf_alloc(void)32 static 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 
48 err_buf:
49 	kfree(buf);
50 err:
51 	return NULL;
52 }
53 
tty_audit_buf_free(struct tty_audit_buf * buf)54 static 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 
tty_audit_log(const char * description,dev_t dev,unsigned char * data,size_t size)61 static 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  */
tty_audit_buf_push(struct tty_audit_buf * buf)91 static 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  */
tty_audit_exit(void)112 void 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  */
tty_audit_fork(struct signal_struct * sig)129 void 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  */
tty_audit_tiocsti(struct tty_struct * tty,char ch)137 void 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  */
tty_audit_push(void)154 int 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  */
tty_audit_buf_get(void)177 static 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  */
tty_audit_add_data(struct tty_struct * tty,const void * data,size_t size)202 void 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