agetty: Prevent cursor escape

Starting with 5de97519, 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 <sbrabec@suse.cz>
(cherry picked from commit 20b405c0fea29675e1fb54b894eb1c18459f9d50)

diff --git a/term-utils/agetty.c b/term-utils/agetty.c
index 72c00e1cc7ecb24d0d14ab8b7e5208d7832a68c9..de490175d80e8eefa6f52c7fea931f913a56c064 100644 (file)
--- a/term-utils/agetty.c
+++ b/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;
                        }