From b12822247796ddc6ea1dded16b9960d2c3d47c4e Mon Sep 17 00:00:00 2001
From: Inrin <inrin@caesia.net>
Date: Sun, 24 May 2020 23:22:34 +0200
Subject: [PATCH] Add maximum padding to fit IPv6-Addresses

We use a fixed padding for the From column to fit the maximum of a
minimized IPv6-LL-Address and it's interface.
---
 src/lastlog.c | 23 ++++++++++++++++++++---
 1 file changed, 20 insertions(+), 3 deletions(-)

diff --git a/src/lastlog.c b/src/lastlog.c
index c1caedb0..492ac67e 100644
--- a/src/lastlog.c
+++ b/src/lastlog.c
@@ -42,6 +42,9 @@
 #include <sys/types.h>
 #include <time.h>
 #include <assert.h>
+#ifdef HAVE_LL_HOST
+#include <net/if.h>
+#endif
 #include "defines.h"
 #include "prototypes.h"
 #include "getdef.h"
@@ -109,6 +112,10 @@ static void print_one (/*@null@*/const struct passwd *pw)
 	char ptime[80];
 #endif
 
+#ifdef HAVE_LL_HOST
+	int maxIPv6Addrlen;
+#endif
+
 	if (NULL == pw) {
 		return;
 	}
@@ -150,7 +157,17 @@ static void print_one (/*@null@*/const struct passwd *pw)
 	/* Print the header only once */
 	if (!once) {
 #ifdef HAVE_LL_HOST
-		puts (_("Username         Port     From             Latest"));
+		/*
+		 * ll_host is in minimized form, thus the maximum IPv6 address possible is
+		 * 8*4+7 = 39 characters.
+		 * RFC 4291 2.5.6 states that for LL-addresses fe80+only the interface ID is set,
+		 * thus having a maximum size of 25+1+IFNAMSIZ.
+		 * POSIX says IFNAMSIZ should be 16 characters long including the null byte, thus
+		 * 25+1+IFNAMSIZ >= 42 > 39
+		 */
+		/* Link-Local address + % + Interfacename */
+		maxIPv6Addrlen = 25+1+IFNAMSIZ;
+		printf (_("Username         Port     From%*sLatest\n"), maxIPv6Addrlen-3, " ");
 #else
 		puts (_("Username                Port     Latest"));
 #endif
@@ -172,8 +189,8 @@ static void print_one (/*@null@*/const struct passwd *pw)
 	}
 
 #ifdef HAVE_LL_HOST
-	printf ("%-16s %-8.8s %-16.16s %s\n",
-	        pw->pw_name, ll.ll_line, ll.ll_host, cp);
+	printf ("%-16s %-8.8s %*s%s\n",
+	        pw->pw_name, ll.ll_line, -maxIPv6Addrlen, ll.ll_host, cp);
 #else
 	printf ("%-16s\t%-8.8s %s\n",
 	        pw->pw_name, ll.ll_line, cp);