getty: prevent sending empty login names to login(1)

Hello,

this patch prevents getty(8) from sending empty login names to login(1).

To reproduce the bug, type some characters, erase the entire line and press
enter/return.

---
 libexec/getty/main.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/libexec/getty/main.c b/libexec/getty/main.c
index 74b3aa27779..5726d5d6838 100644
--- a/libexec/getty/main.c
+++ b/libexec/getty/main.c
@@ -59,7 +59,7 @@
 
 struct termios tmode, omode;
 
-int crmod, digit, lower, upper;
+int crmod, lower;
 
 char	hostname[HOST_NAME_MAX+1];
 char	globalhostname[HOST_NAME_MAX+1];
@@ -318,7 +318,10 @@ main(int argc, char *argv[])
 				xputs("user names may not start with '-'.");
 				continue;
 			}
-			if (!(upper || lower || digit))
+			for (i = 0; name[i]; i++)
+				if (isalnum(name[i]))
+					break;
+			if (name[i] == '\0')
 				continue;
 			setflags(2);
 			if (crmod) {
@@ -381,7 +384,7 @@ getname(void)
 		syslog(LOG_ERR, "%s: %m", ttyn);
 		exit(1);
 	}
-	crmod = digit = lower = upper = 0;
+	crmod = lower = 0;
 	np = name;
 	for (;;) {
 		oflush();
@@ -409,8 +412,6 @@ getname(void)
 		}
 		if (islower(c))
 			lower = 1;
-		else if (isupper(c))
-			upper = 1;
 		else if (c == ERASE || c == '\b') {
 			if (np > name) {
 				if (*--np == '\033')
@@ -432,8 +433,7 @@ getname(void)
 			prompt();
 			np = name;
 			continue;
-		} else if (isdigit(c))
-			digit++;
+		}
 		if (IG && (c <= ' ' || c > 0176))
 			continue;
 		*np++ = c;
-- 
2.53.0