*
* Licensed under GPLv2, see file LICENSE in this tarball for details.
*/
+
+/*
+ * A typical usage of BB lpd looks as follows:
+ * # tcpsvd -E 0 515 lpd SPOOLDIR [HELPER-PROG [ARGS...]]
+ *
+ * This means a network listener is started on port 515 (default for LP protocol).
+ * When a client connection is made (via lpr) lpd first change its working directory to SPOOLDIR.
+ *
+ * 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 or an ordinary file 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.
+ *
+ * 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 processed data file.
+ *
+ * A good lpr passes control files which when parsed provide 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
+ * $l = name of datafile ("dfAxxx") - file whose content are to be printed
+ *
+ * Thus, a typical helper can be something like this:
+ * #!/bin/sh
+ * cat "$l" >/dev/lp0
+ * mv -f "$l" save/
+ *
+ */
#include "libbb.h"
// TODO: xmalloc_reads is vulnerable to remote OOM attack!
+// strip argument of bad chars
+static char *sane(char *str)
+{
+ char *s = str;
+ char *p = s;
+ while (*s) {
+ if (isalnum(*s) || '-' == *s) {
+ *p++ = *s;
+ }
+ s++;
+ }
+ *p = '\0';
+ return str;
+}
+
+static void exec_helper(const char *fname, char **argv)
+{
+ char *p, *q, *file;
+ char *our_env[12];
+ int env_idx;
+
+ // read control file
+ file = q = xmalloc_open_read_close(fname, NULL);
+ // delete control file
+ unlink(fname);
+ // parse control file by "\n"
+ env_idx = 0;
+ while ((p = strchr(q, '\n')) != NULL
+ && isalpha(*q)
+ && env_idx < ARRAY_SIZE(our_env)
+ ) {
+ *p++ = '\0';
+ // here q is a line of <SYM><VALUE>
+ // let us set environment string <SYM>=<VALUE>
+ // N.B. setenv is leaky!
+ // We have to use putenv(malloced_str),
+ // and unsetenv+free (in parent)
+ our_env[env_idx] = xasprintf("%c=%s", *q, q+1);
+ putenv(our_env[env_idx]);
+ env_idx++;
+ // next line, plz!
+ q = p;
+ }
+
+ if (vfork() == 0) {
+ // CHILD
+ // we are the helper. we wanna be silent
+ // this call reopens stdio fds to "/dev/null"
+ // (no daemonization is done)
+ bb_daemonize_or_rexec(DAEMON_DEVNULL_STDIO | DAEMON_ONLY_SANITIZE, NULL);
+ BB_EXECVP(*argv, argv);
+ _exit(127);
+ }
+
+ // PARENT (or vfork error)
+ // clean up...
+ free(file);
+ while (--env_idx >= 0) {
+ *strchrnul(our_env[env_idx], '=') = '\0';
+ unsetenv(our_env[env_idx]);
+ }
+}
+
int lpd_main(int argc, char *argv[]) MAIN_EXTERNALLY_VISIBLE;
int lpd_main(int argc ATTRIBUTE_UNUSED, char *argv[])
{
return EXIT_FAILURE;
}
- // spool directory contains either links to real printer devices or just simple files
- // these links or files are called "queues"
- // OR
- // if a directory named as given queue exists within spool directory
- // then LPD enters spooling mode and just dumps both control and data files to it
-
// goto spool directory
- if (argv[1])
- xchdir(argv[1]);
+ if (*++argv)
+ xchdir(*argv++);
// parse command: "\x2QUEUE_NAME\n"
queue = s + 1;
*strchrnul(s, '\n') = '\0';
// protect against "/../" attacks
- if (queue[0] == '.' || strstr(queue, "/."))
+ if (!*sane(queue))
return EXIT_FAILURE;
// queue is a directory -> chdir to it and enter spooling mode
*fname++ = '\0';
if (spooling) {
// spooling mode: dump both files
- // make "/../" attacks in file names ineffective
- xchroot(".");
// job in flight has mode 0200 "only writable"
- fd = xopen3(fname, O_CREAT | O_WRONLY | O_TRUNC | O_EXCL, 0200);
+ fd = xopen3(sane(fname), O_CREAT | O_WRONLY | O_TRUNC | O_EXCL, 0200);
} else {
// non-spooling mode:
// 2: control file (ignoring), 3: data file
expected_len, real_len);
return EXIT_FAILURE;
}
+ // chmod completely downloaded file as "readable+writable" ...
+ if (spooling) {
+ fchmod(fd, 0600);
+ // ... and accumulate dump state.
+ // N.B. after all files are dumped spooling should be 1+2+3==6
+ spooling += s[0];
+ }
+ close(fd); // NB: can do close(-1). Who cares?
+
+ // are all files dumped? -> spawn spool helper
+ if (6 == spooling && *argv) {
+ fname[0] = 'c'; // pass control file name
+ exec_helper(fname, argv);
+ }
// get ACK and see whether it is NUL (ok)
if (read(STDIN_FILENO, s, 1) != 1 || s[0] != 0) {
// don't send error msg to peer - it obviously
// it can't understand us either
return EXIT_FAILURE;
}
- // chmod completely downloaded job as "readable+writable"
- if (spooling)
- fchmod(fd, 0600);
- close(fd); // NB: can do close(-1). Who cares?
free(s);
} /* while (1) */
}
projects / oweals / busybox.git / commitdiff