agetty: Prevent cursor escape

Starting with 5de9751, it is possible to escape the login dialog on the
screen by arrow characters or using escape sequences.

Since full processing of escape sequences and ignore them would be
complicated, use a work around: instead of sending ESC to output, send a
printable character.

It could cause a rendering regression in a very obscure condition: compiled
without IUTF8, encoding is ISO-11548-1 and BRAILLE PATTERN DOTS-1245 is
part of login name. I believe that it is out of supported combinations.

Signed-off-by: Stanislav Brabec <[email protected]>

term-utils/agetty.c

@@ -2289,7 +2289,14 @@ static char *get_logname(struct issue *ie, struct options *op, struct termios *t
 				if ((size_t)(bp - logname) >= sizeof(logname) - 1)
 					log_err(_("%s: input overrun"), op->tty);
 				if ((tp->c_lflag & ECHO) == 0)
-					write_all(1, &c, 1);	/* echo the character */
+					/* Visualize escape sequence instead of its execution */
+					if (ascval == CTL('['))
+						/* Ideally it should be "\xe2\x90\x9b"
+						 * if (op->flags & (F_UTF8)),
+						 * but only some fonts contain it */
+						write_all(1, "^[", 2);
+					else
+						write_all(1, &c, 1);	/* echo the character */
 				*bp++ = ascval;			/* and store it */
 				break;
 			}