void xsetgid(gid_t gid);
void xsetuid(uid_t uid);
void xchdir(const char *path);
+void xchroot(const char *path);
void xsetenv(const char *key, const char *value);
void xunlink(const char *pathname);
void xstat(const char *pathname, struct stat *buf);
extern ssize_t safe_read(int fd, void *buf, size_t count);
extern ssize_t nonblock_safe_read(int fd, void *buf, size_t count);
+// NB: will return short read on error, not -1,
+// if some data was read before error occurred
extern ssize_t full_read(int fd, void *buf, size_t count);
extern void xread(int fd, void *buf, size_t count);
extern unsigned char xread_char(int fd);
extern void *xmalloc_open_read_close(const char *filename, size_t *sizep);
extern ssize_t safe_write(int fd, const void *buf, size_t count);
+// NB: will return short write on error, not -1,
+// if some data was written before error occurred
extern ssize_t full_write(int fd, const void *buf, size_t count);
extern void xwrite(int fd, const void *buf, size_t count);
/* vi: set sw=4 ts=4: */
/*
- * micro lpd - a small non-queueing lpd
+ * micro lpd
*
* Copyright (C) 2008 by Vladimir Dronnikov <dronnikov@gmail.com>
*
*/
#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[])
{
- char *s;
+ 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;
+ }
- // goto spool directory
// spool directory contains either links to real printer devices or just simple files
// these links or files are called "queues"
- if (!argv[1])
- bb_show_usage();
+ // 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
- xchdir(argv[1]);
+ // goto spool directory
+ if (argv[1])
+ xchdir(argv[1]);
- xdup2(1, 2);
+ // parse command: "\x2QUEUE_NAME\n"
+ queue = s + 1;
+ *strchrnul(s, '\n') = '\0';
- // read command
- s = xmalloc_reads(STDIN_FILENO, NULL);
+ // protect against "/../" attacks
+ if (queue[0] == '.' || strstr(queue, "/."))
+ return EXIT_FAILURE;
- // N.B. we keep things simple
- // only "receive job" command is meaningful here...
- if (2 == *s) {
- char *queue;
+ // queue is a directory -> chdir to it and enter spooling mode
+ spooling = chdir(queue) + 1; /* 0: cannot chdir, 1: done */
- // parse command: "\x2QUEUE_NAME\n"
- queue = s + 1;
- *strchrnul(s, '\n') = '\0';
+ xdup2(STDOUT_FILENO, STDERR_FILENO);
- while (1) {
- // signal OK
- write(STDOUT_FILENO, "", 1);
- // get subcommand
- s = xmalloc_reads(STDIN_FILENO, NULL);
- if (!s)
- return EXIT_SUCCESS; // EOF (probably)
- // valid s must be of form: SUBCMD | LEN | SP | FNAME
- // N.B. we bail out on any error
- // control or data file follows
- if (2 == s[0] || 3 == s[0]) {
- int fd;
- size_t len;
- // 2: control file (ignoring), 3: data file
- fd = -1;
- if (3 == s[0])
- fd = xopen(queue, O_RDWR | O_APPEND);
- // get data length
- *strchrnul(s, ' ') = '\0';
- len = xatou(s + 1);
- // dump exactly len bytes to file, or die
- bb_copyfd_exact_size(STDIN_FILENO, fd, len);
- close(fd); // NB: can do close(-1). Who cares?
- free(s);
- // got no ACK? -> bail out
- if (safe_read(STDIN_FILENO, s, 1) <= 0 || s[0]) {
- // don't talk to peer - it obviously
- // don't follow the protocol
- return EXIT_FAILURE;
- }
- } else {
- // any other subcommand aborts receiving job
- // N.B. abort subcommand itself doesn't contain
- // fname so it failed earlier...
- break;
- }
- }
- }
+ 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;
- printf("Command %02x not supported\n", (unsigned char)*s);
- return EXIT_FAILURE;
+ *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) */
}
*/
static void get_response_or_say_and_die(const char *errmsg)
{
- static const char newline = '\n';
- char buf = ' ';
+ ssize_t sz;
+ char buf[128];
fflush(stdout);
- safe_read(STDOUT_FILENO, &buf, 1);
- if ('\0' != buf) {
+ buf[0] = ' ';
+ sz = safe_read(STDOUT_FILENO, buf, 1);
+ if ('\0' != buf[0]) {
// request has failed
- bb_error_msg("error while %s. Server said:", errmsg);
- safe_write(STDERR_FILENO, &buf, 1);
- logmode = 0; /* no error messages from bb_copyfd_eof() pls */
- bb_copyfd_eof(STDOUT_FILENO, STDERR_FILENO);
- safe_write(STDERR_FILENO, &newline, 1);
+ // try to make sure last char is '\n', but do not add
+ // superfluous one
+ sz = full_read(STDOUT_FILENO, buf + 1, 126);
+ bb_error_msg("error while %s%s", errmsg,
+ (sz > 0 ? ". Server said:" : ""));
+ if (sz > 0) {
+ // sz = (bytes in buf) - 1
+ if (buf[sz] != '\n')
+ buf[++sz] = '\n';
+ safe_write(STDERR_FILENO, buf, sz + 1);
+ }
xfunc_die();
}
}
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