1/* vi: set sw=4 ts=4: */
2/*
3 * micro lpd
4 *
5 * Copyright (C) 2008 by Vladimir Dronnikov <dronnikov@gmail.com>
6 *
7 * Licensed under GPLv2, see file LICENSE in this tarball for details.
8 */
9
10/*
11 * A typical usage of BB lpd looks as follows:
12 * # tcpsvd -E 0 515 lpd [SPOOLDIR] [HELPER-PROG [ARGS...]]
13 *
14 * This starts TCP listener on port 515 (default for LP protocol).
15 * When a client connection is made (via lpr) lpd first changes its
16 * working directory to SPOOLDIR (current dir is the default).
17 *
18 * SPOOLDIR is the spool directory which contains printing queues
19 * and should have the following structure:
20 *
21 * SPOOLDIR/
22 *      <queue1>
23 *      ...
24 *      <queueN>
25 *
26 * <queueX> can be of two types:
27 *      A. a printer character device, an ordinary file or a link to such;
28 *      B. a directory.
29 *
30 * In case A lpd just dumps the data it receives from client (lpr) to the
31 * end of queue file/device. This is non-spooling mode.
32 *
33 * In case B lpd enters spooling mode. It reliably saves client data along
34 * with control info in two unique files under the queue directory. These
35 * files are named dfAXXXHHHH and cfAXXXHHHH, where XXX is the job number
36 * and HHHH is the client hostname. Unless a printing helper application
37 * is specified lpd is done at this point.
38 *
39 * NB: file names are produced by peer! They actually may be anything at all.
40 * lpd only sanitizes them (by removing most non-alphanumerics).
41 *
42 * If HELPER-PROG (with optional arguments) is specified then lpd continues
43 * to process client data:
44 *      1. it reads and parses control file (cfA...). The parse process
45 *      results in setting environment variables whose values were passed
46 *      in control file; when parsing is complete, lpd deletes control file.
47 *      2. it spawns specified helper application. It is then
48 *      the helper application who is responsible for both actual printing
49 *      and deleting of processed data file.
50 *
51 * A good lpr passes control files which when parsed provides the following
52 * variables:
53 * $H = host which issues the job
54 * $P = user who prints
55 * $C = class of printing (what is printed on banner page)
56 * $J = the name of the job
57 * $L = print banner page
58 * $M = the user to whom a mail should be sent if a problem occurs
59 *
60 * We specifically filter out and NOT provide:
61 * $l = name of datafile ("dfAxxx") - file whose content are to be printed
62 *
63 * lpd provides $DATAFILE instead - the ACTUAL name
64 * of the datafile under which it was saved.
65 * $l would be not reliable (you would be at mercy of remote peer).
66 *
67 * Thus, a typical helper can be something like this:
68 * #!/bin/sh
69 * cat ./"$DATAFILE" >/dev/lp0
70 * mv -f ./"$DATAFILE" save/
71 */
72
73#include "libbb.h"
74
75// strip argument of bad chars
76static char *sane(char *str)
77{
78	char *s = str;
79	char *p = s;
80	while (*s) {
81		if (isalnum(*s) || '-' == *s || '_' == *s) {
82			*p++ = *s;
83		}
84		s++;
85	}
86	*p = '\0';
87	return str;
88}
89
90static char *xmalloc_read_stdin(void)
91{
92	// SECURITY:
93	size_t max = 4 * 1024; // more than enough for commands!
94	return xmalloc_reads(STDIN_FILENO, NULL, &max);
95}
96
97int lpd_main(int argc, char *argv[]) MAIN_EXTERNALLY_VISIBLE;
98int lpd_main(int argc UNUSED_PARAM, char *argv[])
99{
100	int spooling = spooling; // for compiler
101	char *s, *queue;
102	char *filenames[2];
103
104	// goto spool directory
105	if (*++argv)
106		xchdir(*argv++);
107
108	// error messages of xfuncs will be sent over network
109	xdup2(STDOUT_FILENO, STDERR_FILENO);
110
111	// nullify ctrl/data filenames
112	memset(filenames, 0, sizeof(filenames));
113
114	// read command
115	s = queue = xmalloc_read_stdin();
116	// we understand only "receive job" command
117	if (2 != *queue) {
118 unsupported_cmd:
119		printf("Command %02x %s\n",
120			(unsigned char)s[0], "is not supported");
121		goto err_exit;
122	}
123
124	// parse command: "2 | QUEUE_NAME | '\n'"
125	queue++;
126	// protect against "/../" attacks
127	// *strchrnul(queue, '\n') = '\0'; - redundant, sane() will do
128	if (!*sane(queue))
129		return EXIT_FAILURE;
130
131	// queue is a directory -> chdir to it and enter spooling mode
132	spooling = chdir(queue) + 1; // 0: cannot chdir, 1: done
133	// we don't free(s), we might need "queue" var later
134
135	while (1) {
136		char *fname;
137		int fd;
138		// int is easier than ssize_t: can use xatoi_u,
139		// and can correctly display error returns (-1)
140		int expected_len, real_len;
141
142		// signal OK
143		safe_write(STDOUT_FILENO, "", 1);
144
145		// get subcommand
146		// valid s must be of form: "SUBCMD | LEN | space | FNAME"
147		// N.B. we bail out on any error
148		s = xmalloc_read_stdin();
149		if (!s) { // (probably) EOF
150			char *p, *q, var[2];
151
152			// non-spooling mode or no spool helper specified
153			if (!spooling || !*argv)
154				return EXIT_SUCCESS; // the only non-error exit
155			// spooling mode but we didn't see both ctrlfile & datafile
156			if (spooling != 7)
157				goto err_exit; // reject job
158
159			// spooling mode and spool helper specified -> exec spool helper
160			// (we exit 127 if helper cannot be executed)
161			var[1] = '\0';
162			// read and delete ctrlfile
163			q = xmalloc_xopen_read_close(filenames[0], NULL);
164			unlink(filenames[0]);
165			// provide datafile name
166			// we can use leaky setenv since we are about to exec or exit
167			xsetenv("DATAFILE", filenames[1]);
168			// parse control file by "\n"
169			while ((p = strchr(q, '\n')) != NULL && isalpha(*q)) {
170				*p++ = '\0';
171				// q is a line of <SYM><VALUE>,
172				// we are setting environment string <SYM>=<VALUE>.
173				// Ignoring "l<datafile>", exporting others:
174				if (*q != 'l') {
175					var[0] = *q++;
176					xsetenv(var, q);
177				}
178				q = p; // next line
179			}
180			// helper should not talk over network.
181			// this call reopens stdio fds to "/dev/null"
182			// (no daemonization is done)
183			bb_daemonize_or_rexec(DAEMON_DEVNULL_STDIO | DAEMON_ONLY_SANITIZE, NULL);
184			BB_EXECVP_or_die(argv);
185		}
186
187		// validate input.
188		// we understand only "control file" or "data file" cmds
189		if (2 != s[0] && 3 != s[0])
190			goto unsupported_cmd;
191		if (spooling & (1 << (s[0]-1))) {
192			printf("Duplicated subcommand\n");
193			goto err_exit;
194		}
195		// get filename
196		*strchrnul(s, '\n') = '\0';
197		fname = strchr(s, ' ');
198		if (!fname) {
199// bad_fname:
200			printf("No or bad filename\n");
201			goto err_exit;
202		}
203		*fname++ = '\0';
204//		// s[0]==2: ctrlfile, must start with 'c'
205//		// s[0]==3: datafile, must start with 'd'
206//		if (fname[0] != s[0] + ('c'-2))
207//			goto bad_fname;
208		// get length
209		expected_len = bb_strtou(s + 1, NULL, 10);
210		if (errno || expected_len < 0) {
211			printf("Bad length\n");
212			goto err_exit;
213		}
214		if (2 == s[0] && expected_len > 16 * 1024) {
215			// SECURITY:
216			// ctrlfile can't be big (we want to read it back later!)
217			printf("File is too big\n");
218			goto err_exit;
219		}
220
221		// open the file
222		if (spooling) {
223			// spooling mode: dump both files
224			// job in flight has mode 0200 "only writable"
225			sane(fname);
226			fd = open3_or_warn(fname, O_CREAT | O_WRONLY | O_TRUNC | O_EXCL, 0200);
227			if (fd < 0)
228				goto err_exit;
229			filenames[s[0] - 2] = xstrdup(fname);
230		} else {
231			// non-spooling mode:
232			// 2: control file (ignoring), 3: data file
233			fd = -1;
234			if (3 == s[0])
235				fd = xopen(queue, O_RDWR | O_APPEND);
236		}
237
238		// signal OK
239		safe_write(STDOUT_FILENO, "", 1);
240
241		// copy the file
242		real_len = bb_copyfd_size(STDIN_FILENO, fd, expected_len);
243		if (real_len != expected_len) {
244			printf("Expected %d but got %d bytes\n",
245				expected_len, real_len);
246			goto err_exit;
247		}
248		// get EOF indicator, see whether it is NUL (ok)
249		// (and don't trash s[0]!)
250		if (safe_read(STDIN_FILENO, &s[1], 1) != 1 || s[1] != 0) {
251			// don't send error msg to peer - it obviously
252			// doesn't follow the protocol, so probably
253			// it can't understand us either
254			goto err_exit;
255		}
256
257		if (spooling) {
258			// chmod completely downloaded file as "readable+writable"
259			fchmod(fd, 0600);
260			// accumulate dump state
261			// N.B. after all files are dumped spooling should be 1+2+4==7
262			spooling |= (1 << (s[0]-1)); // bit 1: ctrlfile; bit 2: datafile
263		}
264
265		free(s);
266		close(fd); // NB: can do close(-1). Who cares?
267
268		// NB: don't do "signal OK" write here, it will be done
269		// at the top of the loop
270	} // while (1)
271
272 err_exit:
273	// don't keep corrupted files
274	if (spooling) {
275#define i spooling
276		for (i = 2; --i >= 0; )
277			if (filenames[i])
278				unlink(filenames[i]);
279	}
280	return EXIT_FAILURE;
281}
282