lpd: spool mode added by Vladimir

lpr: more robust error reporting
*: introduce and use xchroot
libbb: full_read/write now will report partial data counts prior to error
isdirectory.c: style fixes

lpd_main                                             249     486    +237
xchroot                                                -      29     +29
get_response_or_say_and_die                          110     139     +29
full_write                                            52      60      +8
full_read                                             55      63      +8
static.newline                                         1       -      -1
switch_root_main                                     404     400      -4
chpst_main                                          1089    1079     -10
getopt32                                            1370    1359     -11
chroot_main                                          115     101     -14
------------------------------------------------------------------------------
(add/remove: 1/1 grow/shrink: 4/4 up/down: 311/-40)           Total: 271 bytes
   text    data     bss     dec     hex filename
 798472     728    7484  806684   c4f1c busybox_old
 798775     728    7484  806987   c504b busybox_unstripped

1 files changed, 92 insertions, 56 deletions

diff --git a/printutils/lpd.c b/printutils/lpd.c
index ed3d9d100..916fd6213 100644
--- a/printutils/lpd.c
+++ b/printutils/lpd.c
@@ -1,6 +1,6 @@
 /* vi: set sw=4 ts=4: */
 /*
- * micro lpd - a small non-queueing lpd
+ * micro lpd
  *
  * Copyright (C) 2008 by Vladimir Dronnikov <dronnikov@gmail.com>
  *
@@ -8,72 +8,108 @@
  */
 #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) */
 }