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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: * 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). * This starts TCP listener on port 515 (default for LP protocol).
* When a client connection is made (via lpr) lpd first change its working directory to SPOOLDIR. * 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 * SPOOLDIR is the spool directory which contains printing queues
* and should have the following structure: * and should have the following structure:
@ -23,44 +24,50 @@
* <queueN> * <queueN>
* *
* <queueX> can be of two types: * <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. * B. a directory.
* *
* In case A lpd just dumps the data it receives from client (lpr) to the * 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. * 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 case B lpd enters spooling mode. It reliably saves client data along
* in two unique files under the queue directory. These files are named dfAXXXHHHH and cfAXXXHHHH, * with control info in two unique files under the queue directory. These
* where XXX is the job number and HHHH is the client hostname. Unless a printing helper application * 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. * 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). * lpd only sanitizes them (by removing most non-alphanumerics).
* *
* If HELPER-PROG (with optional arguments) is specified then lpd continues to process client data: * If HELPER-PROG (with optional arguments) is specified then lpd continues
* 1. it reads and parses control file (cfA...). The parse process results in setting environment * to process client data:
* variables whose values were passed in control file; when parsing is complete, lpd deletes * 1. it reads and parses control file (cfA...). The parse process
* control file. * results in setting environment variables whose values were passed
* 2. it spawns specified helper application. It is then the helper application who is responsible * in control file; when parsing is complete, lpd deletes control file.
* for both actual printing and deleting processed data 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 * $H = host which issues the job
* $P = user who prints * $P = user who prints
* $C = class of printing (what is printed on banner page) * $C = class of printing (what is printed on banner page)
* $J = the name of the job * $J = the name of the job
* $L = print banner page * $L = print banner page
* $M = the user to whom a mail should be sent if a problem occurs * $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 * $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. * of the datafile under which it was saved.
* $l is not reliable (you are at mercy of remote peer), DON'T USE IT. * $l would be not reliable (you would be at mercy of remote peer).
* *
* Thus, a typical helper can be something like this: * Thus, a typical helper can be something like this:
* #!/bin/sh * #!/bin/sh
* cat "$l" >/dev/lp0 * cat ./"$DATAFILE" >/dev/lp0
* mv -f "$l" save/ * mv -f ./"$DATAFILE" save/
*/ */
#include "libbb.h" #include "libbb.h"
@ -87,6 +94,8 @@ static void exec_helper(char **filenames, char **argv)
char *p, *q; char *p, *q;
char var[2]; char var[2];
var[1] = '\0';
// read and delete ctrlfile // read and delete ctrlfile
q = xmalloc_open_read_close(filenames[0], NULL); q = xmalloc_open_read_close(filenames[0], NULL);
unlink(filenames[0]); unlink(filenames[0]);
@ -97,11 +106,13 @@ static void exec_helper(char **filenames, char **argv)
&& isalpha(*q) && isalpha(*q)
) { ) {
*p++ = '\0'; *p++ = '\0';
// here q is a line of <SYM><VALUE> // q is a line of <SYM><VALUE>,
// let us set environment string <SYM>=<VALUE> // we are setting environment string <SYM>=<VALUE>.
var[0] = *q++; // Ignoring "l<datafile>", exporting others:
var[1] = '\0'; if (*q != 'l') {
xsetenv(var, q); var[0] = *q++;
xsetenv(var, q);
}
// next line, plz! // next line, plz!
q = p; q = p;
} }
@ -110,7 +121,7 @@ static void exec_helper(char **filenames, char **argv)
// (no daemonization is done) // (no daemonization is done)
bb_daemonize_or_rexec(DAEMON_DEVNULL_STDIO | DAEMON_ONLY_SANITIZE, NULL); bb_daemonize_or_rexec(DAEMON_DEVNULL_STDIO | DAEMON_ONLY_SANITIZE, NULL);
BB_EXECVP(*argv, argv); BB_EXECVP(*argv, argv);
exit(0); exit(127); // it IS error if helper cannot be executed!
} }
static char *xmalloc_read_stdin(void) 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 lpd_main(int argc ATTRIBUTE_UNUSED, char *argv[])
{ {
int spooling = spooling; // for compiler int spooling = spooling; // for compiler
int seen;
char *s, *queue; char *s, *queue;
char *filenames[2]; 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 // error messages of xfuncs will be sent over network
xdup2(STDOUT_FILENO, STDERR_FILENO); xdup2(STDOUT_FILENO, STDERR_FILENO);
filenames[0] = NULL; // ctrlfile name // nullify ctrl/data filenames
filenames[1] = NULL; // datafile name memset(filenames, 0, sizeof(filenames));
// read command // read command
s = queue = xmalloc_read_stdin(); 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 // queue is a directory -> chdir to it and enter spooling mode
spooling = chdir(queue) + 1; // 0: cannot chdir, 1: done spooling = chdir(queue) + 1; // 0: cannot chdir, 1: done
seen = 0; // we don't free(s), we might need "queue" var later
// we don't free(queue), we might need it later
while (1) { while (1) {
char *fname; char *fname;
@ -175,7 +184,7 @@ int lpd_main(int argc ATTRIBUTE_UNUSED, char *argv[])
// N.B. we bail out on any error // N.B. we bail out on any error
s = xmalloc_read_stdin(); s = xmalloc_read_stdin();
if (!s) { // (probably) EOF if (!s) { // (probably) EOF
if (spooling /* && 6 != spooling - always true */) { if (spooling /* && 7 != spooling - always true */) {
// we didn't see both ctrlfile & datafile! // we didn't see both ctrlfile & datafile!
goto err_exit; 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 // we understand only "control file" or "data file" cmds
if (2 != s[0] && 3 != s[0]) if (2 != s[0] && 3 != s[0])
goto unsupported_cmd; goto unsupported_cmd;
if (seen & (s[0] - 1)) { if (spooling & (1 << (s[0]-1))) {
printf("Duplicated subcommand\n"); printf("Duplicated subcommand\n");
goto err_exit; goto err_exit;
} }
seen &= (s[0] - 1); // bit 1: ctrlfile; bit 2: datafile
// get filename // get filename
*strchrnul(s, '\n') = '\0'; *strchrnul(s, '\n') = '\0';
fname = strchr(s, ' '); fname = strchr(s, ' ');
@ -243,9 +251,10 @@ int lpd_main(int argc ATTRIBUTE_UNUSED, char *argv[])
goto err_exit; goto err_exit;
} }
// get ACK and see whether it is NUL (ok) // 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 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 // it can't understand us either
goto err_exit; goto err_exit;
} }
@ -254,14 +263,15 @@ int lpd_main(int argc ATTRIBUTE_UNUSED, char *argv[])
// chmod completely downloaded file as "readable+writable" // chmod completely downloaded file as "readable+writable"
fchmod(fd, 0600); fchmod(fd, 0600);
// accumulate dump state // accumulate dump state
// N.B. after all files are dumped spooling should be 1+2+3==6 // N.B. after all files are dumped spooling should be 1+2+4==7
spooling += s[0]; spooling |= (1 << (s[0]-1)); // bit 1: ctrlfile; bit 2: datafile
} }
free(s); free(s);
close(fd); // NB: can do close(-1). Who cares? close(fd); // NB: can do close(-1). Who cares?
// spawn spool helper and exit if all files are dumped // spawn spool helper and exit if all files are dumped
if (6 == spooling && *argv) { if (7 == spooling && *argv) {
// signal OK // signal OK
safe_write(STDOUT_FILENO, "", 1); safe_write(STDOUT_FILENO, "", 1);
// does not return (exits 0) // does not return (exits 0)
@ -272,10 +282,10 @@ int lpd_main(int argc ATTRIBUTE_UNUSED, char *argv[])
err_exit: err_exit:
// don't keep corrupted files // don't keep corrupted files
if (spooling) { if (spooling) {
if (filenames[0]) #define i spooling
unlink(filenames[0]); for (i = 2; --i >= 0; )
if (filenames[1]) if (filenames[i])
unlink(filenames[1]); unlink(filenames[i]);
} }
return EXIT_FAILURE; return EXIT_FAILURE;
} }