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/* 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 tarball for details.
*/
#include "libbb.h"
// TODO: xmalloc_reads is vulnerable to remote OOM attack!
int lpd_main(int argc, char *argv[]) MAIN_EXTERNALLY_VISIBLE;
int lpd_main(int argc, char *argv[])
{
int spooling;
char *s, *queue;
// read command
s = xmalloc_reads(STDIN_FILENO, NULL);
// we understand only "receive job" command
if (2 != *s) {
unsupported_cmd:
printf("Command %02x %s\n",
(unsigned char)s[0], "is not supported");
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]);
// parse command: "\x2QUEUE_NAME\n"
queue = s + 1;
*strchrnul(s, '\n') = '\0';
// protect against "/../" attacks
if (queue[0] == '.' || strstr(queue, "/."))
return EXIT_FAILURE;
// queue is a directory -> chdir to it and enter spooling mode
spooling = chdir(queue) + 1; /* 0: cannot chdir, 1: done */
xdup2(STDOUT_FILENO, STDERR_FILENO);
while (1) {
char *fname;
int fd;
// int is easier than ssize_t: can use xatoi_u,
// and can correctly display error returns (-1)
int expected_len, real_len;
// signal OK
write(STDOUT_FILENO, "", 1);
// get subcommand
s = xmalloc_reads(STDIN_FILENO, NULL);
if (!s)
return EXIT_SUCCESS; // probably EOF
// we understand only "control file" or "data file" cmds
if (2 != s[0] && 3 != s[0])
goto unsupported_cmd;
*strchrnul(s, '\n') = '\0';
// valid s must be of form: SUBCMD | LEN | SP | FNAME
// N.B. we bail out on any error
fname = strchr(s, ' ');
if (!fname) {
printf("Command %02x %s\n",
(unsigned char)s[0], "lacks filename");
return EXIT_FAILURE;
}
*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);
} else {
// non-spooling mode:
// 2: control file (ignoring), 3: data file
fd = -1;
if (3 == s[0])
fd = xopen(queue, O_RDWR | O_APPEND);
}
expected_len = xatoi_u(s + 1);
real_len = bb_copyfd_size(STDIN_FILENO, fd, expected_len);
if (spooling && real_len != expected_len) {
unlink(fname); // don't keep corrupted files
printf("Expected %d but got %d bytes\n",
expected_len, real_len);
return EXIT_FAILURE;
}
// 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
// don't follow the protocol, so probably
// 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) */
}
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