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lpd: debugging by Vladimir: he found vda's breakage (trashed s[0])!

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This commit is contained in:
Denis Vlasenko 2008-03-24 21:19:51 +00:00
parent cee01cfb2e
commit f39653e306
1 changed files with 52 additions and 42 deletions
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94
printutils/lpd.c
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@ -9,10 +9,11 @@
/*
* A typical usage of BB lpd looks as follows:
* # tcpsvd -E 0 515 lpd SPOOLDIR [HELPER-PROG [ARGS...]]
* # 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.
* 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:
@ -23,44 +24,50 @@
* <queueN>
*
* <queueX> can be of two types:
* A. a printer character device or an ordinary file a link to such;
* 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
* 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!
* 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 processed data file.
* 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 provide the following variables:
* 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 also provides $DATAFILE environment variable - the ACTUAL name
* lpd provides $DATAFILE instead - the ACTUAL name
* of the datafile under which it was saved.
* $l is not reliable (you are at mercy of remote peer), DON'T USE IT.
* $l would be not reliable (you would be at mercy of remote peer).
*
* Thus, a typical helper can be something like this:
* #!/bin/sh
* cat "$l" >/dev/lp0
* mv -f "$l" save/
* cat ./"$DATAFILE" >/dev/lp0
* mv -f ./"$DATAFILE" save/
*/
#include "libbb.h"
@ -87,6 +94,8 @@ static void exec_helper(char **filenames, char **argv)
char *p, *q;
char var[2];
var[1] = '\0';
// read and delete ctrlfile
q = xmalloc_open_read_close(filenames[0], NULL);
unlink(filenames[0]);
@ -97,11 +106,13 @@ static void exec_helper(char **filenames, char **argv)
&& isalpha(*q)
) {
*p++ = '\0';
// here q is a line of <SYM><VALUE>
// let us set environment string <SYM>=<VALUE>
var[0] = *q++;
var[1] = '\0';
xsetenv(var, q);
// 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);
}
// next line, plz!
q = p;
}
@ -110,7 +121,7 @@ static void exec_helper(char **filenames, char **argv)
// (no daemonization is done)
bb_daemonize_or_rexec(DAEMON_DEVNULL_STDIO | DAEMON_ONLY_SANITIZE, NULL);
BB_EXECVP(*argv, argv);
exit(0);
exit(127); // it IS error if helper cannot be executed!
}
static char *xmalloc_read_stdin(void)
@ -124,7 +135,6 @@ int lpd_main(int argc, char *argv[]) MAIN_EXTERNALLY_VISIBLE;
int lpd_main(int argc ATTRIBUTE_UNUSED, char *argv[])
{
int spooling = spooling; // for compiler
int seen;
char *s, *queue;
char *filenames[2];
@ -135,8 +145,8 @@ int lpd_main(int argc ATTRIBUTE_UNUSED, char *argv[])
// error messages of xfuncs will be sent over network
xdup2(STDOUT_FILENO, STDERR_FILENO);
filenames[0] = NULL; // ctrlfile name
filenames[1] = NULL; // datafile name
// nullify ctrl/data filenames
memset(filenames, 0, sizeof(filenames));
// read command
s = queue = xmalloc_read_stdin();
@ -157,8 +167,7 @@ int lpd_main(int argc ATTRIBUTE_UNUSED, char *argv[])
// queue is a directory -> chdir to it and enter spooling mode
spooling = chdir(queue) + 1; // 0: cannot chdir, 1: done
seen = 0;
// we don't free(queue), we might need it later
// we don't free(s), we might need "queue" var later
while (1) {
char *fname;
@ -175,7 +184,7 @@ int lpd_main(int argc ATTRIBUTE_UNUSED, char *argv[])
// N.B. we bail out on any error
s = xmalloc_read_stdin();
if (!s) { // (probably) EOF
if (spooling /* && 6 != spooling - always true */) {
if (spooling /* && 7 != spooling - always true */) {
// we didn't see both ctrlfile & datafile!
goto err_exit;
}
@ -187,11 +196,10 @@ int lpd_main(int argc ATTRIBUTE_UNUSED, char *argv[])
// we understand only "control file" or "data file" cmds
if (2 != s[0] && 3 != s[0])
goto unsupported_cmd;
if (seen & (s[0] - 1)) {
if (spooling & (1 << (s[0]-1))) {
printf("Duplicated subcommand\n");
goto err_exit;
}
seen &= (s[0] - 1); // bit 1: ctrlfile; bit 2: datafile
// get filename
*strchrnul(s, '\n') = '\0';
fname = strchr(s, ' ');
@ -243,9 +251,10 @@ int lpd_main(int argc ATTRIBUTE_UNUSED, char *argv[])
goto err_exit;
}
// get ACK and see whether it is NUL (ok)
if (safe_read(STDIN_FILENO, s, 1) != 1 || s[0] != 0) {
// (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
// don't follow the protocol, so probably
// doesn't follow the protocol, so probably
// it can't understand us either
goto err_exit;
}
@ -254,14 +263,15 @@ int lpd_main(int argc ATTRIBUTE_UNUSED, char *argv[])
// 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+3==6
spooling += s[0];
// 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?
// spawn spool helper and exit if all files are dumped
if (6 == spooling && *argv) {
if (7 == spooling && *argv) {
// signal OK
safe_write(STDOUT_FILENO, "", 1);
// does not return (exits 0)
@ -272,10 +282,10 @@ int lpd_main(int argc ATTRIBUTE_UNUSED, char *argv[])
err_exit:
// don't keep corrupted files
if (spooling) {
if (filenames[0])
unlink(filenames[0]);
if (filenames[1])
unlink(filenames[1]);
#define i spooling
for (i = 2; --i >= 0; )
if (filenames[i])
unlink(filenames[i]);
}
return EXIT_FAILURE;
}