crontab: do not destroy STDIN_FILENO, editor may need it (crontab -e)

vi: deal with EOF/error on stdin and with input NULs

function                                             old     new   delta
crontab_main                                         623     642     +19
edit_file                                            901     906      +5
readit                                               331     318     -13

2 files changed, 35 insertions, 32 deletions

diff --git a/editors/vi.c b/editors/vi.c
index 27f2a3abd..02bdbb37b 100644
--- a/editors/vi.c
+++ b/editors/vi.c
@@ -147,10 +147,10 @@ struct globals {
 #endif
 
 	smallint editing;        // >0 while we are editing a file
-	                         // [code audit says "can be 0 or 1 only"]
+	                         // [code audit says "can be 0, 1 or 2 only"]
 	smallint cmd_mode;       // 0=command  1=insert 2=replace
 	int file_modified;       // buffer contents changed (counter, not flag!)
-	int last_file_modified; // = -1;
+	int last_file_modified;  // = -1;
 	int fn_start;            // index of first cmd line file name
 	int save_argc;           // how many file names on cmd line
 	int cmdcnt;              // repetition count
@@ -623,7 +623,7 @@ static void edit_file(char *fn)
 		// These are commands that change text[].
 		// Remember the input for the "." command
 		if (!adding2q && ioq_start == NULL
-		 && strchr(modifying_cmds, c)
+		 && c != '\0' && strchr(modifying_cmds, c)
 		) {
 			start_new_cmd_q(c);
 		}
@@ -645,8 +645,8 @@ static void edit_file(char *fn)
 	}
 	//-------------------------------------------------------------------
 
-	place_cursor(rows, 0, FALSE);	// go to bottom of screen
-	clear_to_eol();		// Erase to end of line
+	place_cursor(rows - 1, 0, FALSE); // go to bottom of screen
+	clear_to_eol(); // erase to end of line
 	cookmode();
 #undef cur_line
 }
@@ -2009,9 +2009,9 @@ static void start_new_cmd_q(char c)
 {
 	// get buffer for new cmd
 	// if there is a current cmd count put it in the buffer first
-	if (cmdcnt > 0)
+	if (cmdcnt > 0) {
 		lmc_len = sprintf(last_modifying_cmd, "%d%c", cmdcnt, c);
-	else { // just save char c onto queue
+	} else { // just save char c onto queue
 		last_modifying_cmd[0] = c;
 		lmc_len = 1;
 	}
@@ -2157,21 +2157,21 @@ static void winch_sig(int sig UNUSED_PARAM)
 //----- Come here when we get a continue signal -------------------
 static void cont_sig(int sig UNUSED_PARAM)
 {
-	rawmode();			// terminal to "raw"
-	last_status_cksum = 0;	// force status update
-	redraw(TRUE);		// re-draw the screen
+	rawmode(); // terminal to "raw"
+	last_status_cksum = 0; // force status update
+	redraw(TRUE); // re-draw the screen
 
 	signal(SIGTSTP, suspend_sig);
 	signal(SIGCONT, SIG_DFL);
-	kill(my_pid, SIGCONT);
+	kill(my_pid, SIGCONT); // huh? why? we are already "continued"...
 }
 
 //----- Come here when we get a Suspend signal -------------------
 static void suspend_sig(int sig UNUSED_PARAM)
 {
-	place_cursor(rows - 1, 0, FALSE);	// go to bottom of screen
-	clear_to_eol();		// Erase to end of line
-	cookmode();			// terminal to "cooked"
+	place_cursor(rows - 1, 0, FALSE); // go to bottom of screen
+	clear_to_eol(); // erase to end of line
+	cookmode(); // terminal to "cooked"
 
 	signal(SIGCONT, cont_sig);
 	signal(SIGTSTP, SIG_DFL);
@@ -2247,18 +2247,20 @@ static char readit(void)	// read (maybe cursor) key from stdin
 
 	fflush(stdout);
 	n = chars_to_parse;
-	// get input from User- are there already input chars in Q?
+	// get input from User - are there already input chars in Q?
 	if (n <= 0) {
 		// the Q is empty, wait for a typed char
+ again:
 		n = safe_read(STDIN_FILENO, readbuffer, sizeof(readbuffer));
-		if (n < 0) {
-			if (errno == EBADF || errno == EFAULT || errno == EINVAL
-			 || errno == EIO)
-				editing = 0; // want to exit
-			errno = 0;
-		}
-		if (n <= 0)
-			return 0;       // error
+		if (n <= 0) {
+			place_cursor(rows - 1, 0, FALSE); // go to bottom of screen
+			clear_to_eol(); // erase to end of line
+			cookmode(); // terminal to "cooked"
+			bb_error_msg_and_die("can't read user input");
+		}
+		/* elsewhere we can get very confused by NULs */
+		if (readbuffer[0] == '\0')
+			goto again;
 		if (readbuffer[0] == 27) {
 			// This is an ESC char. Is this Esc sequence?
 			// Could be bare Esc key. See if there are any
diff --git a/miscutils/crontab.c b/miscutils/crontab.c
index ef6d94375..673b558c3 100644
--- a/miscutils/crontab.c
+++ b/miscutils/crontab.c
@@ -93,6 +93,7 @@ int crontab_main(int argc UNUSED_PARAM, char **argv)
 	char *new_fname;
 	char *user_name;  /* -u USER */
 	int fd;
+	int src_fd;
 	int opt_ler;
 
 	/* file [opts]     Replace crontab from file
@@ -144,15 +145,15 @@ int crontab_main(int argc UNUSED_PARAM, char **argv)
 		bb_show_usage();
 
 	/* Read replacement file under user's UID/GID/group vector */
+	src_fd = STDIN_FILENO;
 	if (!opt_ler) { /* Replace? */
 		if (!argv[0])
 			bb_show_usage();
 		if (NOT_LONE_DASH(argv[0])) {
-			fd = open_as_user(pas, argv[0]);
-			if (fd < 0)
+			src_fd = open_as_user(pas, argv[0]);
+			if (src_fd < 0)
 				bb_error_msg_and_die("user %s cannot read %s",
 						pas->pw_name, argv[0]);
-			xmove_fd(fd, STDIN_FILENO);
 		}
 	}
 
@@ -180,23 +181,23 @@ int crontab_main(int argc UNUSED_PARAM, char **argv)
 		tmp_fname = xasprintf("%s.%u", crontab_dir, (unsigned)getpid());
 		/* No O_EXCL: we don't want to be stuck if earlier crontabs
 		 * were killed, leaving stale temp file behind */
-		fd = xopen3(tmp_fname, O_RDWR|O_CREAT|O_TRUNC, 0600);
-		xmove_fd(fd, STDIN_FILENO);
-		fchown(STDIN_FILENO, pas->pw_uid, pas->pw_gid);
+		src_fd = xopen3(tmp_fname, O_RDWR|O_CREAT|O_TRUNC, 0600);
+		fchown(src_fd, pas->pw_uid, pas->pw_gid);
 		fd = open(pas->pw_name, O_RDONLY);
 		if (fd >= 0) {
-			bb_copyfd_eof(fd, STDIN_FILENO);
+			bb_copyfd_eof(fd, src_fd);
 			close(fd);
+			xlseek(src_fd, 0, SEEK_SET);
 		}
+		close_on_exec_on(src_fd); /* don't want editor to see this fd */
 		edit_file(pas, tmp_fname);
-		xlseek(STDIN_FILENO, 0, SEEK_SET);
 		/* fall through */
 
 	case 0: /* Replace (no -l, -e, or -r were given) */
 		new_fname = xasprintf("%s.new", pas->pw_name);
 		fd = open(new_fname, O_WRONLY|O_CREAT|O_TRUNC|O_APPEND, 0600);
 		if (fd >= 0) {
-			bb_copyfd_eof(STDIN_FILENO, fd);
+			bb_copyfd_eof(src_fd, fd);
 			close(fd);
 			xrename(new_fname, pas->pw_name);
 		} else {