summaryrefslogtreecommitdiff
path: root/networking/fakeidentd.c
blob: 7eac4806539ffc3c803b3eb1b87e1734d72af4a2 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
/* vi: set sw=4 ts=4: */
/*
 * A fake identd server
 *
 * Adapted to busybox by Thomas Lundquist <thomasez@zelow.no>
 * Original Author: Tomi Ollila <too@iki.fi>
 *                  http://www.guru-group.fi/~too/sw/
 *
 * Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
 */

#include "busybox.h"
#include <sys/syslog.h>
#include <sys/uio.h>


#define IDENT_PORT  113
#define MAXCONNS    20
#define MAXIDLETIME 45

static const char ident_substr[] = " : USERID : UNIX : ";
enum { ident_substr_len = sizeof(ident_substr) - 1 };
#define PIDFILE "/var/run/identd.pid"

/*
 * We have to track the 'first connection socket' so that we
 * don't go around closing file descriptors for non-clients.
 *
 * descriptor setup normally
 *  0 = server socket
 *  1 = syslog fd (hopefully -- otherwise this won't work)
 *  2 = connection socket after detached from tty. standard error before that
 *  3 - 2 + MAXCONNS = rest connection sockets
 *
 * To try to make sure that syslog fd is what is "requested", the that fd
 * is closed before openlog() call.  It can only severely fail if fd 0
 * is initially closed.
 */
#define FCS 2

/*
 * FD of the connection is always the index of the connection structure
 * in `conns' array + FCS
 */
static struct {
	char buf[20];
	int len;
	time_t lasttime;
} conns[MAXCONNS];

/* When using global variables, bind those at least to a structure. */
static struct {
	const char *identuser;
	fd_set readfds;
	int conncnt;
} G;

/*
 * Prototypes
 */
static void reply(int s, char *buf);
static void replyError(int s, char *buf);

static const char *nobodystr = "nobody"; /* this needs to be declared like this */
static char *bind_ip_address = "0.0.0.0";

static void movefd(int from, int to)
{
	if (from != to) {
		dup2(from, to);
		close(from);
	}
}

static void inetbind(void)
{
	int s, port;
	struct sockaddr_in addr;
	int len = sizeof(addr);
	struct servent *se;

	se = getservbyname("identd", "tcp");
	port = IDENT_PORT;
	if (se)
		port = se->s_port;

	s = xsocket(AF_INET, SOCK_STREAM, 0);

	setsockopt_reuseaddr(s);

	memset(&addr, 0, sizeof(addr));
	addr.sin_addr.s_addr = inet_addr(bind_ip_address);
	addr.sin_family = AF_INET;
	addr.sin_port = htons(port);

	xbind(s, (struct sockaddr *)&addr, len);
	xlisten(s, 5);

	movefd(s, 0);
}

static void handlexitsigs(int signum)
{
	if (unlink(PIDFILE) < 0)
		close(open(PIDFILE, O_WRONLY|O_CREAT|O_TRUNC, 0644));
	exit(0);
}

/* May succeed. If not, won't care. */
static void writepid(uid_t nobody, uid_t nogrp)
{
	char buf[sizeof(int)*3 + 2];
	int fd = open(PIDFILE, O_WRONLY|O_CREAT|O_TRUNC, 0664);

	if (fd < 0)
		return;

	sprintf(buf, "%d\n", getpid());
	write(fd, buf, strlen(buf));
	fchown(fd, nobody, nogrp);
	close(fd);

	/* should this handle ILL, ... (see signal(7)) */
	signal(SIGTERM, handlexitsigs);
	signal(SIGINT,  handlexitsigs);
	signal(SIGQUIT, handlexitsigs);
}

/* return 0 as parent, 1 as child */
static int godaemon(void)
{
	uid_t nobody, nogrp;
	struct passwd *pw;

	switch (fork()) {
	case -1:
		bb_perror_msg_and_die("fork");

	case 0:
		pw = getpwnam(nobodystr);
		if (pw == NULL)
			bb_error_msg_and_die("cannot find uid/gid of user '%s'", nobodystr);
		nobody = pw->pw_uid;
		nogrp = pw->pw_gid;
		writepid(nobody, nogrp);

		close(0);
		inetbind();
		xsetgid(nogrp);
		xsetuid(nobody);
		close(1);
		close(2);

		signal(SIGHUP, SIG_IGN);
		signal(SIGPIPE, SIG_IGN); /* connection closed when writing (raises ???) */

		setsid();

		return 1;
	}

	return 0;
}

static void deleteConn(int s)
{
	int i = s - FCS;

	close(s);

	G.conncnt--;

	/*
	 * Most of the time there is 0 connections. Most often that there
	 * is connections, there is just one connection. When this one connection
	 * closes, i == G.conncnt = 0 -> no copying.
	 * When there is more than one connection, the oldest connections closes
	 * earlier on average. When this happens, the code below starts copying
	 * the connection structure w/ highest index to the place which which is
	 * just deleted. This means that the connection structures are no longer
	 * in chronological order. I'd quess this means that when there is more
	 * than 1 connection, on average every other connection structure needs
	 * to be copied over the time all these connections are deleted.
	 */
	if (i != G.conncnt) {
		memcpy(&conns[i], &conns[G.conncnt], sizeof(conns[0]));
		movefd(G.conncnt + FCS, s);
	}

	FD_CLR(G.conncnt + FCS, &G.readfds);
}

static int closeOldest(void)
{
	time_t min = conns[0].lasttime;
	int idx = 0;
	int i;

	for (i = 1; i < MAXCONNS; i++)
		if (conns[i].lasttime < min)
			idx = i;

	replyError(idx + FCS, "X-SERVER-TOO-BUSY");
	close(idx + FCS);

	return idx;
}

static int checkInput(char *buf, int len, int l)
{
	int i;
	for (i = len; i < len + l; ++i)
		if (buf[i] == '\n')
			return 1;
	return 0;
}

int fakeidentd_main(int argc, char **argv)
{
	/* This applet is an inetd-style daemon */
	openlog(applet_name, 0, LOG_DAEMON);
	logmode = LOGMODE_SYSLOG;

	memset(conns, 0, sizeof(conns));
	memset(&G, 0, sizeof(G));
	FD_ZERO(&G.readfds);
	FD_SET(0, &G.readfds);

	/* handle -b <ip> parameter */
	getopt32(argc, argv, "b:", &bind_ip_address);
	/* handle optional REPLY STRING */
	if (optind < argc)
		G.identuser = argv[optind];
	else
		G.identuser = nobodystr;

	/* daemonize and have the parent return */
	if (godaemon() == 0)
		return 0;

	/* main loop where we process all events and never exit */
	while (1) {
		fd_set rfds = G.readfds;
		struct timeval tv = { 15, 0 };
		int i;
		int tim = time(NULL);

		select(G.conncnt + FCS, &rfds, NULL, NULL, G.conncnt? &tv: NULL);

		for (i = G.conncnt - 1; i >= 0; i--) {
			int s = i + FCS;

			if (FD_ISSET(s, &rfds)) {
				char *buf = conns[i].buf;
				unsigned int len = conns[i].len;
				unsigned int l;

				if ((l = read(s, buf + len, sizeof(conns[0].buf) - len)) > 0) {
					if (checkInput(buf, len, l)) {
						reply(s, buf);
						goto deleteconn;
					} else if (len + l >= sizeof(conns[0].buf)) {
						replyError(s, "X-INVALID-REQUEST");
						goto deleteconn;
					} else {
						conns[i].len += l;
					}
				} else {
					goto deleteconn;
				}

				conns[i].lasttime = tim;
				continue;

deleteconn:
				deleteConn(s);
			} else {
				/* implement as time_after() in linux kernel sources ... */
				if (conns[i].lasttime + MAXIDLETIME <= tim) {
					replyError(s, "X-TIMEOUT");
					deleteConn(s);
				}
			}
		}

		if (FD_ISSET(0, &rfds)) {
			int s = accept(0, NULL, 0);

			if (s < 0) {
				if (errno != EINTR) /* EINTR */
					bb_perror_msg("accept");
			} else {
				if (G.conncnt == MAXCONNS)
					i = closeOldest();
				else
					i = G.conncnt++;

				movefd(s, i + FCS); /* move if not already there */
				FD_SET(i + FCS, &G.readfds);

				conns[i].len = 0;
				conns[i].lasttime = time(NULL);
			}
		}
	} /* end of while (1) */

	return 0;
}

static int parseAddrs(char *ptr, char **myaddr, char **heraddr);
static void reply(int s, char *buf)
{
	char *myaddr, *heraddr;

	myaddr = heraddr = NULL;

	if (parseAddrs(buf, &myaddr, &heraddr))
		replyError(s, "X-INVALID-REQUEST");
	else {
		struct iovec iv[6];
		iv[0].iov_base = myaddr;               iv[0].iov_len = strlen(myaddr);
		iv[1].iov_base = ", ";                 iv[1].iov_len = 2;
		iv[2].iov_base = heraddr;              iv[2].iov_len = strlen(heraddr);
		iv[3].iov_base = (void *)ident_substr; iv[3].iov_len = ident_substr_len;
		iv[4].iov_base = (void *)G.identuser;  iv[4].iov_len = strlen(G.identuser);
		iv[5].iov_base = "\r\n";               iv[5].iov_len = 2;
		writev(s, iv, 6);
	}
}

static void replyError(int s, char *buf)
{
	struct iovec iv[3];
	iv[0].iov_base = "0, 0 : ERROR : ";   iv[0].iov_len = 15;
	iv[1].iov_base = buf;                 iv[1].iov_len = strlen(buf);
	iv[2].iov_base = "\r\n";              iv[2].iov_len = 2;
	writev(s, iv, 3);
}

static int chmatch(char c, char *chars)
{
	for (; *chars; chars++)
		if (c == *chars)
			return 1;
	return 0;
}

static int skipchars(char **p, char *chars)
{
	while (chmatch(**p, chars))
		(*p)++;
	if (**p == '\r' || **p == '\n')
		return 0;
	return 1;
}

static int parseAddrs(char *ptr, char **myaddr, char **heraddr)
{
	/* parse <port-on-server> , <port-on-client> */

	if (!skipchars(&ptr, " \t"))
		return -1;

	*myaddr = ptr;

	if (!skipchars(&ptr, "1234567890"))
		return -1;

	if (!chmatch(*ptr, " \t,"))
		return -1;

	*ptr++ = '\0';

	if (!skipchars(&ptr, " \t,") )
		return -1;

	*heraddr = ptr;

	skipchars(&ptr, "1234567890");

	if (!chmatch(*ptr, " \n\r"))
		return -1;

	*ptr = '\0';

	return 0;
}