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

1 files changed, 52 insertions, 42 deletions

diff --git a/printutils/lpd.c b/printutils/lpd.c
index 4008e4396..f4c902c79 100644
--- a/printutils/lpd.c
+++ b/printutils/lpd.c
@@ -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;
 }