From 703faa82ffbd4fa30e8ec2a05893d4fba498790e Mon Sep 17 00:00:00 2001
From: vnxme <46669194+vnxme@users.noreply.github.com>
Date: Thu, 21 Jan 2021 17:00:24 +0300
Subject: [PATCH] interfaces.inc: Improve guess_interface_from_ip() (#4523)

---
 src/etc/inc/interfaces.inc | 37 ++++++++++++++-----------------------
 1 file changed, 14 insertions(+), 23 deletions(-)

diff --git a/src/etc/inc/interfaces.inc b/src/etc/inc/interfaces.inc
index e48983510..654299a00 100644
--- a/src/etc/inc/interfaces.inc
+++ b/src/etc/inc/interfaces.inc
@@ -3757,34 +3757,25 @@ function get_real_interface($interface = 'wan', $family = 'all')
 
 function guess_interface_from_ip($ipaddress)
 {
-    if (!is_ipaddr($ipaddress)) {
+    if (is_ipaddrv4($ipaddress)) {
+        $family = "inet";
+    } elseif (is_ipaddrv6($ipaddress)) {
+        $family = "inet6";
+    } else {
         return false;
     }
-    if (is_ipaddrv4($ipaddress)) {
-        /* create a route table we can search */
-        exec("/usr/bin/netstat -rnWf inet", $output, $ret);
-        foreach ($output as $line) {
-            if (preg_match("/^[0-9]+\.[0-9]+\.[0-9]+\.[0-9]+\/[0-9]+[ ]+link[#]/", $line)) {
-                $fields = preg_split("/[ ]+/", $line);
-                if (ip_in_subnet($ipaddress, $fields[0])) {
-                    return $fields[5];
-                }
-            }
-        }
-    }
-    /* FIXME: This works from cursory testing, regexp might need fine tuning */
-    if (is_ipaddrv6($ipaddress)) {
-        /* create a route table we can search */
-        exec("/usr/bin/netstat -rnWf inet6", $output, $ret);
-        foreach ($output as $line) {
-            if (preg_match("/[0-9a-f]+[:]+[0-9a-f]+[:]+[\/][0-9]+/", $line)) {
-                $fields = preg_split("/[ ]+/", $line);
-                if (ip_in_subnet($ipaddress, $fields[0])) {
-                    return $fields[5];
-                }
+
+    /* create a route table we can search */
+    exec("/usr/bin/netstat -rnWf ".$family, $output, $ret);
+    foreach ($output as $line) {
+        $fields = preg_split("/\s+/", $line);
+        if (is_subnet($fields[0])) {
+            if (ip_in_subnet($ipaddress, $fields[0])) {
+                return $fields[5];
             }
         }
     }
+
     $ret = exec_command("/sbin/route -n get {$ipaddress} | /usr/bin/awk '/interface/ { print \$2; };'");
     if (empty($ret)) {
         return false;