/* vi: set sw=4 ts=4: */ /* * micro lpd * * Copyright (C) 2008 by Vladimir Dronnikov <dronnikov@gmail.com> * * Licensed under GPLv2, see file LICENSE in this source tree. */ /* * A typical usage of BB lpd looks as follows: * # tcpsvd -E 0 515 lpd [SPOOLDIR] [HELPER-PROG [ARGS...]] * * This starts TCP listener on port 515 (default for LP protocol). * When a client connection is made (via lpr) lpd first changes its * working directory to SPOOLDIR (current dir is the default). * * SPOOLDIR is the spool directory which contains printing queues * and should have the following structure: * * SPOOLDIR/ * <queue1> * ... * <queueN> * * <queueX> can be of two types: * A. a printer character device, an ordinary file or a link to such; * B. a directory. * * In case A lpd just dumps the data it receives from client (lpr) to the * end of queue file/device. This is non-spooling mode. * * In case B lpd enters spooling mode. It reliably saves client data along * with control info in two unique files under the queue directory. These * files are named dfAXXXHHHH and cfAXXXHHHH, where XXX is the job number * and HHHH is the client hostname. Unless a printing helper application * is specified lpd is done at this point. * * NB: file names are produced by peer! They actually may be anything at all. * lpd only sanitizes them (by removing most non-alphanumerics). * * If HELPER-PROG (with optional arguments) is specified then lpd continues * to process client data: * 1. it reads and parses control file (cfA...). The parse process * results in setting environment variables whose values were passed * in control file; when parsing is complete, lpd deletes control file. * 2. it spawns specified helper application. It is then * the helper application who is responsible for both actual printing * and deleting of processed data file. * * A good lpr passes control files which when parsed provides the following * variables: * $H = host which issues the job * $P = user who prints * $C = class of printing (what is printed on banner page) * $J = the name of the job * $L = print banner page * $M = the user to whom a mail should be sent if a problem occurs * * We specifically filter out and NOT provide: * $l = name of datafile ("dfAxxx") - file whose content are to be printed * * lpd provides $DATAFILE instead - the ACTUAL name * of the datafile under which it was saved. * $l would be not reliable (you would be at mercy of remote peer). * * Thus, a typical helper can be something like this: * #!/bin/sh * cat ./"$DATAFILE" >/dev/lp0 * mv -f ./"$DATAFILE" save/ */ //config:config LPD //config: bool "lpd (5.3 kb)" //config: default y //config: help //config: lpd is a print spooling daemon. //applet:IF_LPD(APPLET(lpd, BB_DIR_USR_SBIN, BB_SUID_DROP)) //kbuild:lib-$(CONFIG_LPD) += lpd.o //usage:#define lpd_trivial_usage //usage: "SPOOLDIR [HELPER [ARGS]]" //usage:#define lpd_full_usage "\n\n" //usage: "SPOOLDIR must contain (symlinks to) device nodes or directories" //usage: "\nwith names matching print queue names. In the first case, jobs are" //usage: "\nsent directly to the device. Otherwise each job is stored in queue" //usage: "\ndirectory and HELPER program is called. Name of file to print" //usage: "\nis passed in $DATAFILE variable." //usage: "\nExample:" //usage: "\n tcpsvd -E 0 515 softlimit -m 999999 lpd /var/spool ./print" #include "libbb.h" // strip argument of bad chars static char *sane(char *str) { char *s = str; char *p = s; while (*s) { if (isalnum(*s) || '-' == *s || '_' == *s) { *p++ = *s; } s++; } *p = '\0'; return str; } static char *xmalloc_read_stdin(void) { // SECURITY: size_t max = 4 * 1024; // more than enough for commands! return xmalloc_reads(STDIN_FILENO, &max); } int lpd_main(int argc, char *argv[]) MAIN_EXTERNALLY_VISIBLE; int lpd_main(int argc UNUSED_PARAM, char *argv[]) { int spooling = spooling; // for compiler char *s, *queue; char *filenames[2]; // goto spool directory if (*++argv) xchdir(*argv++); // error messages of xfuncs will be sent over network xdup2(STDOUT_FILENO, STDERR_FILENO); // nullify ctrl/data filenames memset(filenames, 0, sizeof(filenames)); // read command s = queue = xmalloc_read_stdin(); // we understand only "receive job" command if (2 != *queue) { unsupported_cmd: printf("Command %02x %s\n", (unsigned char)s[0], "is not supported"); goto err_exit; } // parse command: "2 | QUEUE_NAME | '\n'" queue++; // protect against "/../" attacks // *strchrnul(queue, '\n') = '\0'; - redundant, sane() will do if (!*sane(queue)) return EXIT_FAILURE; // queue is a directory -> chdir to it and enter spooling mode spooling = chdir(queue) + 1; // 0: cannot chdir, 1: done // we don't free(s), we might need "queue" var later while (1) { char *fname; int fd; // int is easier than ssize_t: can use xatoi_positive, // and can correctly display error returns (-1) int expected_len, real_len; // signal OK safe_write(STDOUT_FILENO, "", 1); // get subcommand // valid s must be of form: "SUBCMD | LEN | space | FNAME" // N.B. we bail out on any error s = xmalloc_read_stdin(); if (!s) { // (probably) EOF char *p, *q, var[2]; // non-spooling mode or no spool helper specified if (!spooling || !*argv) return EXIT_SUCCESS; // the only non-error exit // spooling mode but we didn't see both ctrlfile & datafile if (spooling != 7) goto err_exit; // reject job // spooling mode and spool helper specified -> exec spool helper // (we exit 127 if helper cannot be executed) var[1] = '\0'; // read and delete ctrlfile q = xmalloc_xopen_read_close(filenames[0], NULL); unlink(filenames[0]); // provide datafile name // we can use leaky setenv since we are about to exec or exit xsetenv("DATAFILE", filenames[1]); // parse control file by "\n" while ((p = strchr(q, '\n')) != NULL && isalpha(*q)) { *p++ = '\0'; // q is a line of <SYM><VALUE>, // we are setting environment string <SYM>=<VALUE>. // Ignoring "l<datafile>", exporting others: if (*q != 'l') { var[0] = *q++; xsetenv(var, q); } q = p; // next line } // helper should not talk over network. // this call reopens stdio fds to "/dev/null". bb_daemon_helper(DAEMON_DEVNULL_STDIO); BB_EXECVP_or_die(argv); } // validate input. // we understand only "control file" or "data file" cmds if (2 != s[0] && 3 != s[0]) goto unsupported_cmd; if (spooling & (1 << (s[0]-1))) { puts("Duplicated subcommand"); goto err_exit; } // get filename chomp(s); fname = strchr(s, ' '); if (!fname) { // bad_fname: puts("No or bad filename"); goto err_exit; } *fname++ = '\0'; // // s[0]==2: ctrlfile, must start with 'c' // // s[0]==3: datafile, must start with 'd' // if (fname[0] != s[0] + ('c'-2)) // goto bad_fname; // get length expected_len = bb_strtou(s + 1, NULL, 10); if (errno || expected_len < 0) { puts("Bad length"); goto err_exit; } if (2 == s[0] && expected_len > 16 * 1024) { // SECURITY: // ctrlfile can't be big (we want to read it back later!) puts("File is too big"); goto err_exit; } // open the file if (spooling) { // spooling mode: dump both files // job in flight has mode 0200 "only writable" sane(fname); fd = open3_or_warn(fname, O_CREAT | O_WRONLY | O_TRUNC | O_EXCL, 0200); if (fd < 0) goto err_exit; filenames[s[0] - 2] = xstrdup(fname); } else { // non-spooling mode: // 2: control file (ignoring), 3: data file fd = -1; if (3 == s[0]) fd = xopen(queue, O_RDWR | O_APPEND); } // signal OK safe_write(STDOUT_FILENO, "", 1); // copy the file real_len = bb_copyfd_size(STDIN_FILENO, fd, expected_len); if (real_len != expected_len) { printf("Expected %d but got %d bytes\n", expected_len, real_len); goto err_exit; } // get EOF indicator, see whether it is NUL (ok) // (and don't trash s[0]!) if (safe_read(STDIN_FILENO, &s[1], 1) != 1 || s[1] != 0) { // don't send error msg to peer - it obviously // doesn't follow the protocol, so probably // it can't understand us either goto err_exit; } if (spooling) { // chmod completely downloaded file as "readable+writable" fchmod(fd, 0600); // accumulate dump state // N.B. after all files are dumped spooling should be 1+2+4==7 spooling |= (1 << (s[0]-1)); // bit 1: ctrlfile; bit 2: datafile } free(s); close(fd); // NB: can do close(-1). Who cares? // NB: don't do "signal OK" write here, it will be done // at the top of the loop } // while (1) err_exit: // don't keep corrupted files if (spooling) { #define i spooling for (i = 2; --i >= 0; ) if (filenames[i]) unlink(filenames[i]); } return EXIT_FAILURE; }